Emmanuel Baudouin
email: emmanuel.baudouin@upmc.fr

Hydrogen sulfide impact on seed biology under abiotic stress

Keywords: Seeds, germination, hydrogen sulfide, antioxidants, abiotic stresses

Successful germination is a critical step of plant life cycle that has dramatic impacts on plant performance in natural ecosystems and agrosystems. Paradoxically, seeds can retain viability even after long term exposure to extreme environmental conditions, whereas their germination is possibly modified by only tiny variations of their abiotic environment. Because of the ongoing climate changes that will bring frequent episodes of extreme temperature, rainfall and drought, seed germinating capacity will be dramatically modified, jeopardizing crop yield, plant spreading and survival.

Understanding the mechanisms regulating seed germination under abiotic constraints is therefore critical to develop strategies to mitigate the effects of global climate change.

During the last decade, the central function of redox processes in the control of seed traits, i.e. dormancy, germination or longevity, has been illustrated in both wild and cultivated species. So far, the investigations have essentially considered the role of reactive oxygen species (ROS), and, to a lesser extent, of nitric oxide (NO), in the regulation of seed biology. The emergence of hydrogen sulfide (H2S) as a new element of the cellular redox balance in plants has recently prompted research on this reactive species in the context of seed biology. This review will present and discuss the possible functions of H2S during seed germination, with an emphasis on the mechanisms through which H2S helps mitigate abiotic stress effects and maintain high germination efficiency under penalizing conditions.

Introduction

The emergence of seeds in Spermatophytes has constituted a major step in the evolution of the Green Lineage, and dramatically improved plant species conservation and dispersion. Indeed, the properties of seeds make them particularly adapted for longdistance spreading and long-lasting survival, two crucial traits for success in complex ecosystems. As plants generally produce huge, but also heterogeneous, seed progeny, seeds allow to evolve diversity and conserve the whole genetic information in temporal and spatial manners, even under changing environmental conditions [START_REF] Nonogaki | Seed dormancy and germination-emerging mechanisms and new hypotheses[END_REF].

Conversely, the emergence of a new plant generation is directly dependent upon the capacity of seeds to germinate and give rise to a robust plantlet. Beside seed longevity, seed germination efficiency is therefore a key determinant in competitive ecosystems.

Since the arrival of agriculture, seeds have also been the pillar of human nutrition and still constitute the primary basis of nutrition. Indeed, improving the production of crop seeds, both quantitatively and qualitatively, is a major economic concern for food industry. Moreover, even when they do not represent the outcome of crop production, seeds generally constitute their income. In this view, seeds are expected to germinate rapidly and homogeneously to give rise to robust seedlings.

Improving such seed traits (germination, vigor, and longevity) is therefore highly topical for seed industry and relies on a better understanding of the mechanisms controlling these different responses.

The undergoing deterioration of environmental conditions, including global warming, water scarcity and soil pollution, constitutes a major threat for plant development and growth and eventually for the survival of the less-adapted species within the ecosystems. Seed germination, as it constitutes the early stage of plant cycle, is particularly vulnerable and impacted by environmental stresses (Daszkowska-Golec 2011). On the one hand, stresses directly affect the capacity of seeds to germinate and the early survival of the emerging plantlets. On the other hand, the efficiency of germination, that depends on characteristics (desiccation tolerance, stored reserves, dormancy) acquired during seed development on the mother plant, are strongly modulated by the environmental conditions experienced by the mother plant itself. Seed germination therefore represents an original context to investigate the mechanisms underlying stress response in plants, as well as an important model to evaluate stress mitigation strategies.

Seed germination is a complex multi-step process that starts with the increase of seed water content upon imbibition and ends up with the protrusion of the embryonic radicle through the protective seed coat tissues [START_REF] Bewley | Seed germination and dormancy[END_REF]. In this timeframe, seed metabolism gets reactivated with the sequential resumption of respiration, mRNA translation and gene transcription, and embryonic axis growth operates via cell expansion [START_REF] Bewley | Seed germination and dormancy[END_REF]). Nevertheless, mature seeds are frequently released from mother plants in a dormant state, i.e. unable to germinate under favorable conditions because of blockage processes established during seed development and will properly germinate only after dormancy release [START_REF] Finch-Savage | Seed dormancy and the control of germination[END_REF]. The switch from dormancy to germination relies on the modification of the balance between abscisic acid (ABA) and gibberellins (GA), the former inhibiting germination when the later participates in its completion. Complex networks controlling ABA and GA metabolism and signaling are therefore at the heart of the regulation of seed germination and integrate environmental cues to trigger germination under appropriate conditions [START_REF] Vishal | Regulation of seed germination and abiotic stresses by gibberellins and abscisic acid[END_REF].

During the last decade, key roles played by reactive species derived from oxygen (ROS) or nitrogen (RNS) in the regulation of seed dormancy and germination have been evidenced (for review, [START_REF] Arc | Nitric oxide implication in the control of seed dormancy and germination[END_REF][START_REF] Bailly | The signalling role of ROS in the regulation of seed germination and dormancy[END_REF]. Interestingly, these compounds can exert opposite effects functioning as toxic molecules or positive cellular signals, in seeds but also when whole plants are exposed to environmental stresses [START_REF] Mittler | ROS are good[END_REF][START_REF] Bailly | The signalling role of ROS in the regulation of seed germination and dormancy[END_REF]. More recently, hydrogen sulfide (H2S) emerged as a new reactive species in plants that shares similar characteristics with ROS/RNS and functions in close interplay with these two classes [START_REF] Lisjak | Hydrogen sulfide: environmental factor or signalling molecule?[END_REF][START_REF] Hancock | Harnessing evolutionary toxins for signaling: reactive oxygen species, nitric oxide and hydrogen sulfide in plant cell regulation[END_REF].

The following paragraphs will review the current knowledge on the metabolism and functions of H2S in seeds. A special emphasis will be placed on the role of this molecule during seed germination under abiotic stress.

Hydrogen sulfide metabolism in seeds

As shown in Table 8.1, a series of studies carried out in a range of plant species have evidenced the presence of H2S in seeds [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010b(Zhang et al. , 2010c;;[START_REF] Li | Hydrogen sulfide is a mediator in H2O2-induced seed germination in Jatropha curcas[END_REF][START_REF] Xie | Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression[END_REF][START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF][START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. These reports indicate that H2S content varies in dry seeds between 0.1 and 1.5 µmol• g -1 DW. Two studies carried out in Arabidopsis thaliana evidenced that H2S content rapidly (within 3 to 6 h) increased upon imbibition leading to a high and steady level of H2S for up to 24-48 h [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF][START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. Although the profiles of H2S production in these two studies were similar, the amplitude of the increase was different, i.e. 1.25 [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF]) and 2.7 folds [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. This difference may reflect different experimental procedures for seed germination (15°C and 22°C, respectively). Although no detailed kinetics is available for wheat, an accumulation of H2S was also detected 12 h after imbibition (Zhang et al. 2010c;[START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF]. In contrast to these results, the increase observed in imbibed Jatropha seeds was only slight (1.16 fold) and delayed (after 3 days) [START_REF] Li | Hydrogen sulfide is a mediator in H2O2-induced seed germination in Jatropha curcas[END_REF]. Interestingly, although no increase of H2S content was observed in wheat aleurone layers under control conditions, it was modified upon hormonal treatment, with ABA promoting and GA repressing H2S synthesis [START_REF] Xie | Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression[END_REF]). As a whole, these data support that H2S metabolism is modified during the early steps of seed germination, leading to enhanced H2S concentrations in seeds.

Remarkably, seed exposure to abiotic stresses during the time lapse of imbibition led to dramatic modifications of H2S content (Table 8.1). For instance, H2S content was 1.5 fold higher in wheat kernels exposed to copper stress compared to unstressed grains after 12 h imbibition [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF]. A similar increase was also observed in wheat grains submitted to osmotic (Zhang et al. 2010c) or aluminum stress (Zhang et al. 2010b) and in Jatrophas curcas seeds exposed to oxidative stress [START_REF] Li | Hydrogen sulfide is a mediator in H2O2-induced seed germination in Jatropha curcas[END_REF]. In these different examples, the increase observed is transient and H2S concentrations progressively decreased back to that of unstressed seeds after 2-4 days of imbibition.

In Arabidopsis, the exposure of seeds to high temperature during imbibition did not affect H2S accumulation during the first 12h, but led to a dramatic decrease thereafter, whereas it remained at highest in unstressed seeds [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. Temperature is a major determinant of seed capacity to germinate and the response to temperature is intimately dependent on seed dormancy status that either restricts (high dormancy) or widen (low dormancy) the temperature window allowing proper germination [START_REF] Finch-Savage | Seed dormancy and the control of germination[END_REF]. Conversely, high temperature induces secondary dormancy in Arabidopsis and inhibits germination (thermoinhibition) (Finch-Savage and Footitt 2017). The different patterns of H2S production reported in seeds imbibed at optimal or high temperature may therefore be a cause or a consequence of different levels of dormancy. Based on these seminal works, H2S appears widely produced in plants seeds during normal germination process and under abiotic constraints. A step forward now requires systematic comparisons of H2S level in i) a large sampling of distant botanical families/species, ii) covering a variety of seed biology types (orthodox/recalcitrant seeds, primary/secondary dormant with different dormancy types, ecotypes), and iii) subjected to a panel of abiotic stress conditions (type, intensity, duration, combination). Several metabolic pathways leading to H2S production have been described in plants (Fig. 8.1). On the one hand, H2S is formed as an intermediate during sulfate assimilation by sulfite reductase (SiR), a ferredoxin-dependent enzyme that catalyzes sulfite reduction [START_REF] Gotor | Signaling by hydrogen sulfide and cyanide through post-translational modification[END_REF]. Then, H2S is essentially used as a substrate by Oacetyl-serine thiol lyase (OAS-TL) to synthesize L-cysteine from O-acetyl-L-serine (OAS) [START_REF] Wirtz | O-acetylserine (thiol) lyase: an enigmatic enzyme of plant cysteine biosynthesis revisited in Arabidopsis thaliana[END_REF]). On the other hand, H2S is generated from L-cysteine by Lcysteine desulfhydrase (L-CDes), together with the formation of pyruvate and ammonia [START_REF] Romero | Cysteine and cysteinerelated signaling pathways in Arabidopsis thaliana[END_REF]. It can also be released from D-cysteine in a similar reaction catalyzed by D-cysteine desulfhydrase (D-CDes) [START_REF] Riemenschneider | Isolation and characterization of a D-cysteine desulfhydrase protein from Arabidopsis thaliana[END_REF]. H2S is also formed during the biosynthesis of cyanoalanine from cyanide and cysteine catalyzed by -cyanoalanine synthase (-CAS) [START_REF] García | Mitochondrial beta-cyanoalanine synthase is essential for root hair formation in Arabidopsis thaliana[END_REF]. Finally, OAS-TL possibly catalyzes a reverse reaction, generating H2S and OAS from D-cysteine. As H2S is highly toxic, catabolic pathways also exist that control H2S cellular content. In particular, H2S easily reacts with glutathione disulfide (GSSG) to form glutathione persulfide (GSSH) that is subsequently oxidized to sulfite by the sulfur dioxygenase ETHE1 (Fig. 8.1) [START_REF] Holdorf | Arabidopsis ETHE1 encodes a sulfur dioxygenase that is essential for embryo and endosperm development[END_REF][START_REF] Krüßel | The mitochondrial sulfur dioxygenase ETHYLMALONIC ENCEPHALOPATHY PROTEIN1 is required for amino acid catabolism during carbohydrate starvation and embryo development in Arabidopsis[END_REF].

The activities of the enzymes of H2S metabolism have been analyzed in seeds of different species. Early work by [START_REF] Taylorson | Promotion of seed germination by cyanide[END_REF] evidenced the increase of -CAS activity in imbibed seeds of pigweed (Amaranthus albus) and lettuce (Lactuca sativa). Whereas cytoplasmic -CAS activity remained unchanged upon imbibition, increases of mitochondrial -CAS activity was also observed in imbibed seeds of cocklebur (Xanthium pennsylvanicum), cucumber (Cucumis sativus), barley (Hordeum vulgare) and rice (Oryza sativa) [START_REF] Hasegawa | The presence of two types of βcyanoalanine synthase in germinating seeds and their responses to ethylene[END_REF]. Furthermore, this activity was stimulated by treatment with ethylene in cocklebur seeds [START_REF] Hasegawa | The presence of two types of βcyanoalanine synthase in germinating seeds and their responses to ethylene[END_REF]. In A. thaliana, -CAS activity was rapidly stimulated after imbibition and remained high for 24h [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF]. Despite the modulation of -CAS activity during imbibition, it may not be related to the increase of H2S production. Indeed, the main function of -CAS is the detoxification of cyanide [START_REF] Machingura | The β-cyanoalanine synthase pathway: beyond cyanide detoxification[END_REF]. A rapid increase of cyanide production is observed during germination that may participate in dormancy release and promote germination and cyanide burst might be dissipated by -CAS activation [START_REF] Oracz | Release of sunflower seed dormancy by cyanide: cross-talk with ethylene signalling pathway[END_REF]. Further investigations are therefore required to evaluate if and to which extent -CAS activity may participate in the overall increase of H2S content. More convincingly, CDes appear as a major source of H2S in seeds. Both L-CDes and D-CDes activities have been detected in dry Arabidopsis seeds and strongly increased following imbibition [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF][START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF].

Strikingly, no increase of H2S content was observed in imbibed mutant seeds for LCD (At3g62130) and DES1 (At5g28030), the major L-CDes, which indicates that these enzymes play crucial role in H2S synthesis in seeds [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF][START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. In agreement, seeds overexpressing DES1 presented a constitutively high level of H2S [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. As the increase of DES1 and LCD enzymatic activities correlated with enhanced transcript levels, it is likely that both activities are at least in part regulated at the transcriptional level [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. Finally, high temperature modified DES1 and LCD activities in agreement with the differences in H2S content observed in heat-stressed seeds [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. Likewise, ABA and GA treatments modulated LCD activity in a similar way as H2S content in wheat aleurone layers [START_REF] Xie | Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression[END_REF]. It is therefore likely that L-CDes activities account for H2S synthesis during seed germinating in optimal or stressing conditions.

Hydrogen sulfide and germination capacity

Numerous studies have investigated how germination is impacted when H2S content is modulated in seeds (Table 8.2). For this purpose, different strategies can be carried out including treatments with H2S-releasing molecules (NaHS or GYY4137), treatments with H2S scavenger such as hypotaurine (HT) or H2S synthesis inhibitor such as aminooxyacetic acid (AOA) or propargylglycine (PG), and genetic approaches using mutants or overexpressing lines for enzymes of H2S metabolism. These strategies have been widely used to investigate the role of H2S during seed germination under optimal conditions and to examine the capacity of H2S to alleviate abiotic stress effects during this developmental stage. Several lines of evidence support a role for H2S produced endogenously during germination under optimal conditions. On the one hand, HT, PG and AOA treatments, that decrease H2S concentration, partially inhibited germination in Arabidopsis and Jatropha curcas [START_REF] Li | Hydrogen sulfide is a mediator in H2O2-induced seed germination in Jatropha curcas[END_REF][START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF][START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]). On the other hand, des1 and lcd mutant seeds also exhibited a lower germination rate compared to WT [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]). des1 seed defect was efficiently reverted by the treatment with H2S donor NaSH and was therefore linked to the modification of H2S content. On the other, such phenotype of des1 seeds was hardly observed in freshly harvested dormant treatment appears to mitigate the impact of diverse stress in a same species as illustrated in wheat (Zhang et al. 2010b(Zhang et al. , 2010c;;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. Conversely, the effect of high temperature is partially reversed by H2S in different species, i.e. maize and Arabidopsis [START_REF] Li | Hydrogen sulfide donor sodium hydrosulfideimproved heat tolerance in maize and involvement of proline[END_REF][START_REF] Zhou | Signaling molecule hydrogen sulfide improves seed germination and seedling growth of maize (Zea mays L.) under high temperature by inducing antioxidant system and osmolyte biosynthesis[END_REF][START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. These observations suggest that mechanisms underlying H2S effect control generic aspects of plant response to stress conserved among plant species that will be presented in the next paragraph. When different doses of H2S donors have been assayed, an optimal effect has generally been observed at around 0.5 mM NaSH (Zhang et al. 2010c;[START_REF] Wang | Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway[END_REF][START_REF] Li | Hydrogen sulfide donor sodium hydrosulfideimproved heat tolerance in maize and involvement of proline[END_REF][START_REF] Zhou | Signaling molecule hydrogen sulfide improves seed germination and seedling growth of maize (Zea mays L.) under high temperature by inducing antioxidant system and osmolyte biosynthesis[END_REF]), but it may also be found at concentrations up to 1.5 mM (Zhang et al. 2010b;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. Interestingly, seed priming with NaHS not only alleviated stress during germination, but it may also ameliorate seedling performance under stress, with important outcome for seed industry and farming [START_REF] Zanganeh | Impacts of seed priming with salicylic acid and sodium hydrosulfide on possible metabolic pathway of two amino acids in maize plant under lead stress[END_REF][START_REF] Valivand | Seed priming with H2S and Ca 2+ trigger signal memory that induces cross-adaptation against nickel stress in zucchini seedlings[END_REF].

Molecular mechanisms controlled by H2S in germinating seeds

Although it seems now established that H2S participates in the regulation of seed germination and that the modulation of H2S content is a promising tool for coping with the effects of abiotic stresses during this developmental process, the mechanisms underlying H2S function in seeds are far from being elucidated. In particular, because molecular analyses have been carried out essentially in stressed plants, the mechanisms controlled by H2S during the germination of unstressed seeds can only be speculated by reference to those modulated in seeds germinating under stress. Moreover, evidences are generally correlative and rarely demonstrate a direct effect of H2S, not to speak of the mechanisms involved. The following paragraphs address the most illustrative examples of H2S function described to date, but also more elusive mechanisms that may represent important routes for future investigations.

Interplay with ROS, nitric oxide, and antioxidant defense

The exposure of plants to environmental stresses generally leads to the elevation of ROS level due to the enhanced ROS formation, in particular H 2 O 2 , that are not fully eliminated by the cellular antioxidant machinery. An elevation of H 2 O 2 content has been observed in seeds germinated under penalizing conditions such as excess Cu, Cd, Al or osmotic stresses [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010b(Zhang et al. , 2010c;;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. A similar increase in superoxide (O2 ⦁ -) content can also be observed (Zhang et al. 2010b;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. In these experiments, treatments with NaSH strongly lowered H 2 O 2 and O2 ⦁ -accumulation. H2S treatment limited the impact of oxidative stress as it helped restricting lipid peroxidation and maintaining membrane integrity [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010b(Zhang et al. , 2010c;;[START_REF] Wang | Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway[END_REF][START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. The major effect of NaSH treatment is the stimulation of a range of antioxidant enzymatic activities (superoxide dismutase, catalase and/or ascorbate and guaiacol peroxidases) that account for ROS detoxification [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010b(Zhang et al. , 2010c;;[START_REF] Wang | Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway[END_REF][START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF].

Such induction might include the transcriptional regulation of the corresponding genes [START_REF] Wang | Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway[END_REF]). In addition, Arabidopsis isoform of catalase CAT3 and ascorbate peroxidase APX1 have been identified as direct targets for S-sulfhydration, an H2Sbased post-translational modification of cysteine residues [START_REF] Aroca | S-sulfhydration: a cysteine posttranslational modification in plant systems[END_REF].

Interestingly, the S-sulfhydration of APX1 led to the reversible stimulation of the enzyme activity, therefore providing a direct mechanism of regulation for APX1 by H2S [START_REF] Aroca | S-sulfhydration: a cysteine posttranslational modification in plant systems[END_REF]. Whether this mechanism is operative in seeds is unknown and no information on the S-sulfhydration status of oxidant/antioxidant enzymes is currently available in seeds. In addition to ROS, connections between H2S and nitric oxide (NO), another reactive species, have been proposed [START_REF] Wang | Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway[END_REF]. The authors evidenced that NaSH treatment enhanced NO production in unstressed and salt stressed-imbibed alfalfa seeds. Treatments with the NO scavenger cPTIO impaired the positive effects of NaSH treatment on seed germination and oxidative stress alleviation in salt-stressed seeds [START_REF] Wang | Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway[END_REF].

As mentioned, ROS also have signaling functions and as so, play a critical role in the regulation of seed ability to germinate [START_REF] Bailly | The signalling role of ROS in the regulation of seed germination and dormancy[END_REF]. Indeed, germination can occur only when the H2O2 content in the seed fall into a restricted range referred as the "Oxidative Window", outside of which seeds remain dormant (too low H2O2 concentration) or undergo rapid ageing (too high H2O2 concentration) [START_REF] Bailly | From intracellular signaling networks to cell death: the dual role of reactive oxygen species in seed physiology[END_REF]. Studies carried out in Vigna radiata and Jatropha curcas suggest that H2S could modulate the germination of unstressed seeds through their effect on H2O2 content [START_REF] Li | Hydrogen sulfide is a mediator in H2O2-induced seed germination in Jatropha curcas[END_REF][START_REF] Li | Hydrogen peroxide might be a downstream signal molecule of hydrogen sulfide in seed germination of mung bean (Vigna radiata)[END_REF]. On the one hand, NaSH treatment increased H2O2 content and NaSH and H2O2 treatments stimulated seed germination. On the other hand, impairing endogenous H2O2 formation abolished the stimulation of germination following NaSH treatment, whereas the stimulation of germination by H2O2 was not affected by H2S depletion. So far, the mechanisms underlying this H2S/H2O2 interplay are unknown, so as its possible physiological relevance for the regulation of seed germination capacity.

Although additional investigations are needed to fully establish the relationship between ROS and H2S in germinating seeds and the mechanisms at work, these different examples speak for opposite effects in unstressed and stressed seeds. In the former case, H2S would participate in the lowering of ROS content via stimulation of the antioxidant defense system. In the latter case, it would promote the formation of signaling ROS through mechanisms to be unraveled. Such dual function is reminiscent of that of NO in which it can also promote or decrease ROS accumulation in plants in different physiological contexts [START_REF] Niu | Hydrogen peroxide signaling in plant development and abiotic responses: crosstalk with nitric oxide and calcium[END_REF]. In this view, the H2S/ROS/NO interplay likely constitute a key determinant of seed germination as evidenced in other processes such as stomatal closure (García-Mata and Lamattina 2010).

H2S and seed metabolism

The transition from dry to germinating seeds is achieved during imbibition and includes the rapid resumption of an active metabolism in a finely orchestrated sequence order [START_REF] Bewley | Seed germination and dormancy[END_REF]. At the end of the germination process sensu stricto, the substrates for fueling energetic metabolism and the precursors for macromolecule biosynthesis are provided by the degradation of reserves (starch, triglycerides, proteins) accumulated during seed formation. Therefore, the efficiency of reserve degradation is crucial for seedling establishment before the transition from a heterotrophic to autotrophic metabolism. A series of studies have addressed the effect of H2S treatment on reserve mobilization in unstressed and stressed wheat grains [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010a, b, c;, b, c;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. In this absence of stress, H2S treatment stimulated amylase activities, but not that of esterases [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010b(Zhang et al. , 2010c;;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. Zhang et al. (2010a) further evidenced the rapid stimulation of -amylase activity by H2S and suggested that this activation might rely on the capacity of H2S to reduce S-S bonds and thereby to release bound -amylase to a free and active form. Interestingly, an -amylase-like protein was identified as persulfilated in Arabidopsis which may constitutes another mechanism for the direct regulation of amylase activities by H2S [START_REF] Aroca | Persulfidation proteome reveals the regulation of protein function by hydrogen sulfide in diverse biological processes in Arabidopsis[END_REF]. Under excess Cu, Cd, Al, and osmotic stress, the amylase activities measured in NaSH-pretreated grains are always higher which indicates that the maintenance of a high reserve mobilization capacity might explain part of the better germination observed in these conditions [START_REF] Zhang | Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress[END_REF](Zhang et al. , 2010b(Zhang et al. , 2010c;;[START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF]. In contrast, esterase activities were hardly modified by H2S treatment in the absence of stress, but stimulated by H2S under Cu, Cd and Al stress. The stimulation of hydrolytic activities by H2S treatment is also evidenced by an increase of free reducing sugars and contents of most free amino acid [START_REF] Huang | Hydrogen sulfide promotes wheat grain germination under cadmium stress[END_REF].

Although reserve mobilization represents a key process for early seedling growth, it constitutes a late event in the germination program. So far, no information is available on the possible impact of H2S on metabolic process rapidly restarted after imbibition, such as respiration, primary metabolism, translation or transcription, neither under unstressed nor stressed conditions. As many proteins operating in these processes have recently been identified as direct target for H2S [START_REF] Aroca | Persulfidation proteome reveals the regulation of protein function by hydrogen sulfide in diverse biological processes in Arabidopsis[END_REF], it is likely that the elevation of H2S content in seeds should impact these processes.

H2S and hormone signaling in the regulation of seed germination

The hormonal balance between ABA and GA content and signaling plays a central role in the decision for a seed to germinate. As ABA is also a key regulator of plant response to abiotic stress, interference or interplay between H2S signaling and ABA signaling is strongly expected when considering the regulation of seed germination under stressing conditions. The H2S/ABA connection has been clearly evidenced for other processes regulated by ABA such as stomatal closure [START_REF] García-Mata | Hydrogen sulphide, a novel gasotransmitter involved in guard cell signalling[END_REF]. Genetic tools have been used to modify H2S formation and analyzed for response to ABA [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF][START_REF] Li | Identification of wheat D-cysteine desulfhydrase (TaD-CDes) required for abscisic acid regulation of seed germination, root growth, and stomatal closure in Arabidopsis[END_REF]. No difference of ABA sensitivity during germination was observed in Arabidopsis des1 mutant seeds [START_REF] Baudouin | The significance of hydrogen sulfide for Arabidopsis seed germination[END_REF]. In contrast, the overexpression of wheat D-CDes in Arabidopsis led to an increased sensitivity to ABA and a stronger inhibition of seed germination in transformed lines [START_REF] Li | Identification of wheat D-cysteine desulfhydrase (TaD-CDes) required for abscisic acid regulation of seed germination, root growth, and stomatal closure in Arabidopsis[END_REF], which suggests that H2S could function as an intermediate in ABA signaling in seeds. Further investigations using mutants deficient for ABA synthesis or response should provide additional information on the precise relationship between ABA and H2S signaling in seeds. These data contrast with another report recently published by [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. Indeed, the authors observed that ABA treatment impaired H2S formation, at least partially by repressing DES1 and L-CDes gene transcription. These evidences are in good agreement with a role of H2S in promoting seed germination.

The study by [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF] also brings a new perspective on the possible interconnection between H2S and ABA signaling. The authors evidenced that H2S was required for seed thermotolerance and that the mechanism at work implied the repression of ABA Insensitive 5 (ABI5) transcription [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. ABI5 is a key transcription factor of ABA signaling and a target for multiple post-translational modifications modifying ABA response [START_REF] Yu | Precise protein post-translational modifications modulate ABI5 activity[END_REF]. Under high temperature, the transcriptional regulator HY5 is stabilized in the nucleus, interacts with ABI5 promoter, leading to ABI5 transcription and the repression of seed germination [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF]. This is achieved by the partitioning of the E3 ligase COP1 that is preferentially retained in the cytosol and therefore does not participate in HY5 degradation. In the presence of H2S, COP1 is preferentially located in the nucleus, brings HY5 to degradation, leading to the repression of ABI5 transcription and allowing germination [START_REF] Chen | The hydrogen sulfide signal enhances seed germination tolerance to high temperatures by retaining nuclear COP1 for HY5 degradation[END_REF].

Under high temperature, H2S signaling would therefore counteract ABA signaling at the level of ABI5 transcription and the equilibrium between H2S and ABA contents could represent a new balance for seed germination regulation. Whereas the interplay between ABA and H2S becomes increasingly clear, the possible connections between H2S and GA have been poorly addressed. So far, the only system in which this question has been studied is the GA-triggered cell death occurring in cereal aleurone layer occurring at the later stages of grain germination [START_REF] Fath | Programmed cell death in cereal aleurone[END_REF]. In this context, NaSH treatment was found to delay and partially prevent GA-triggered cell death in wheat and barley aleurone layers, suggesting an antagonistic function between H2S and GA [START_REF] Xie | Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression[END_REF][START_REF] Zhang | The hydrogen sulfide donor NaHS delays programmed cell death in barley aleurone layers by acting as an antioxidant[END_REF]. This is further supported by the fact that H2S functioned synergistically with ABA in preventing aleurone cell death [START_REF] Xie | Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression[END_REF].

The alleviation of cell death relied on the capacity of H2S to lower oxidative stress, in particular, by preventing the collapse of the antioxidant defense [START_REF] Xie | Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression[END_REF][START_REF] Zhang | The hydrogen sulfide donor NaHS delays programmed cell death in barley aleurone layers by acting as an antioxidant[END_REF]. Intriguingly, H2S also stimulated -amylase secretion in barley, a mechanism activated by GA and required for reserve mobilization in the starchy endosperm, suggesting that H2S and GA could also function synergistically [START_REF] Zhang | The hydrogen sulfide donor NaHS delays programmed cell death in barley aleurone layers by acting as an antioxidant[END_REF]. Additional molecular and genetic studies on this system, and more generally on interference between GA and H2S outside of cereal models, are clearly required for supporting whether and understand how these two pathways could be interlinked.

Concluding remarks and open questions

Many studies carried out during the last decade support the strong potential of H2S for stress mitigation during seed germination, and therefore its possible use for translational research in seed science. As the species and stresses that have been analyzed so far remain limited, the coming step will be to evaluate how global H2S effect can be when considering a large range of plant/stress combinations. This is particularly topical as the variable physical and physiological properties of seeds might significantly influence H2S availability when exogenous treatments with H2S are to be used, so as the seed sensitivity towards particular stresses.

Beyond seed stress physiology, the participation of H2S in the regulation of the germination process itself remains underexplored, although it might bring valuable information on the fundamental mechanisms regulating this process. Moreover, it is still unclear or even unknown if and how H2S takes part in processes such as seed development, seed dormancy establishment and release, seed vigor and/or seed longevity. Future approaches are therefore expected to clarify the ins and outs of H2S in seed biology and require intensive efforts towards the unraveling of the mode of action of this compound at the molecular level in seeds. The use of pharmacological and genetic tools, together with the many molecular markers available for model species and the new probes for H2S detection in leaving tissues, should help address these issues. Noteworthy, seed represents a particularly appropriate playground to investigate H2S interplay with other signaling molecules such as hormones or ROS/NO.

Although the interplay between H2S and ABA evidenced in other physiological contexts is probably also operating in seeds, nothing is known for other hormones such as GA, ethylene, auxins or brassinosteroids that all constitute key regulators of seed biology. Together with information from dedicated studies in seeds, more indirect evidence is probably to come from large scale-approaches that have been recently initiated. For instance, the identification of hundreds of proteins directly modified by persulfidation constitutes a reservoir of potential targets, some of which possibly regulated during germination [START_REF] Aroca | Persulfidation proteome reveals the regulation of protein function by hydrogen sulfide in diverse biological processes in Arabidopsis[END_REF]. In addition to proteomic data, the identification of H2S-regulated genes by transcriptomic approaches would help to further unravel the cellular and biochemical processes controlled by H2S signaling in general and seeds in particular.

Fig. 8 . 1

 81 Fig. 8.1 Schematic representation of H2S metabolism in plants. CAS: b-cyanoalanine synthase; D-CDes: D-cysteine desulfhydrase; L-CDes: L-cysteine desulfhydrase; ETHE1: ethylmalonic encephalopathy protein1; GSSH: glutathione persulfide; GSSG: oxidized glutathione; OAS: Oacetylserine; OAS-TL: O-acetyl-L-serine(thiol)lyase; SiR: sulfite reductase.

Table 8

 8

	.1 Detection of H2S in seeds during imbibition
	a Highest [H2S] observed in seeds and corresponding time. b Experiments realized on isolated
	aleurone layers. ABA, abscisic acid; GA, gibberellins; FW, fresh weight; DW, dry weight.

Table 8 .2

 8 Effect of the modulation of H2S on seed germination

AOA: aminoacetic acid; des1: Arabidopsis thaliana L-cysteine desulfhydrase 1 mutant (At5g28030; Salk_103855); DES1-OE: Arabidopsis thaliana L-cysteine desulfhydrase 1 overexpressor; GYY: GYY4137; HT: hypotaurine; lcd: Arabidopsis thaliana L-cysteine desulfhydrase (At3g62130; Salk_082099); NaSH: sodium hydrosulfide; PG: propargylglycine.

Acknowledgements

This work was supported by Sorbonne Université and the Centre National de la Recherche Scientifique.


Alicia Lefrancois
email: alicia.lefrancois@u-picardie.fr

Léa Pecjak
email: lea.pecjak@esc-amiens.com

Sophie Changeur
email: sophie.changeur@u-picardie.fr

PREMIER PRIX Sophie Changeur Marques

Packagings

DE TRANSGRESSION DE MARQUE POSITIVE Marques

DE TRANSGRESSION DE MARQUE POSITIVE Alicia Lefrançois

MARQUES PREMIER PRIX ET PACKAGINGS QUALITATIFS SONT-ILS VRAIMENT ANTINOMIQUES ? UN CAS DE TRANSGRESSION DE MARQUE POSITIVE

Keywords: Marques premier prix, packaging, transgression de marque positive, grande distribution LOWER RANGE PRIVATE "Lower range" private label brands, packaging, positive brand transgressions, mass retail(ing)

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Après de nombreuses années de croissance en France, les MDD -marques de distributeurs -ont progressivement perdu de leur attractivité. Fin avril 2021, elles enregistraient un repli de 3,7 % par rapport à 20201 . Parmi les MDD, les marques premier prix voient leurs ventes reculer le plus fortement. Au sein des causes identifiées, leur positionnement "entrée de gamme" qui n'est plus en adéquation avec les attentes des consommateurs en termes de qualité et ce, tant au niveau des attributs intrinsèques qu'extrinsèques des produits [START_REF] Lacoeuilhe | Marques de distributeurs et publicités comparatives directes des prix : des effets à différencier selon les types de MDD et les catégories de produits[END_REF][START_REF] Hyman | Review of literature -Future research suggestions: Private label brands: Benefits, success factors and future research[END_REF]. Les marques premier prix souffrent en effet d'une perception négative de leur performance produit [START_REF] Lacoeuilhe | Marques de distributeurs et publicités comparatives directes des prix : des effets à différencier selon les types de MDD et les catégories de produits[END_REF][START_REF] Kadekova | The impact of packaging on consumer behavior in the private label market -the case of Slovak consumers under 25 years of age[END_REF]. En conséquence de leurs faibles performances commerciales actuelles, elles sont désormais peu mises en avant dans les enseignes, notamment en termes de merchandising (Lacoeuillhe et al., 2018). Les marques premier prix demeurent pourtant stratégiques pour les enseignes puisqu'elles occupent un créneau de positionnement différent des autres MDD et permettent de réaliser des marges plus élevées par rapport à la vente de marques nationales [START_REF] Sethuraman | Determinants of Store Brand Share[END_REF].

En suivant cette considération opérationnelle, nous pouvons nous demander quels leviers pourraient être exploités afin de relancer ces marques. A cet égard, une réflexion sur le packaging des produits de marque premier prix -notamment au regard du signal de qualité qu'il véhicule -peut être une première piste d'investigation. En effet, le packaging influence la formation de l'attitude des consommateurs envers le produit. Par le biais des formes, couleurs, symboles, typographies et informations qui le composent, le packaging leur transmet des indices notamment au regard de la qualité [START_REF] Magnier | Communicating packaging eco-friendliness: An exploration of consumers' perceptions of eco-designed packaging[END_REF][START_REF] Diallo | Le comportement du consommateur face aux marques de distributeur au Brésil. Une étude qualitative[END_REF]. Il peut donc affecter la manière dont les consommateurs vont évaluer le produit et par incidence, le choisir [START_REF] Magnier | Communicating packaging eco-friendliness: An exploration of consumers' perceptions of eco-designed packaging[END_REF][START_REF] Diallo | Le comportement du consommateur face aux marques de distributeur au Brésil. Une étude qualitative[END_REF]. S'il est admis que des améliorations du packaging contribuent à impacter positivement les décisions d'achat des consommateurs [START_REF] Koutsimanis | Influences of packaging attributes on consumer purchase decisions for fresh produce[END_REF], une interrogation demeure concernant les marques premier prix ; comment les consommateurs réagiraient-ils si ces marques premier prix transgressaient les normes et conventions en lien avec l'aspect habituel de leurs packagings ? Ceci nous amène à la problématique suivante : Comment les consommateurs percevraient-ils et appréhenderaient-ils un packaging de marque premier prix s'il véhiculait un signal de meilleure qualité ?

Nous proposons de traiter ce questionnement au moyen d'une étude qualitative exploratoire alliant techniques projectives et entretiens semi-directifs. Elle nous permettra dans un premier temps d'identifier les caractéristiques extrinsèques d'un packaging de marque premier prix ainsi que leur importance dans la perception du positionnement "entrée de gamme". Dans un second temps, nous étudierons la perception des consommateurs envers un packaging de marque premier prix dont les caractéristiques extrinsèques du packaging véhiculent davantage de signaux de qualité. Nous nous intéresserons également à la manière dont les consommateurs sont affectés par cette transgression de marque positive et comment ils la perçoivent.

Il est attendu que ce travail enrichisse la littérature marketing portant sur les marques premier prix et les transgressions de marques positives. En posant l'hypothèse que "perception de qualité" et "entrée de gamme" ne sont pas de facto antinomiques contrairement au postulat actuel, cette étude permettra de formuler des recommandations opérationnelles pour la création de packagings de marque premier prix équilibrés et donc, de contribuer à relancer ces dernières.

Revue de la littérature

Définition et types de marques de distributeurs. La loi relative aux Nouvelles Régulations Économiques (NRE) définie la marque de distributeur (MDD) comme un « produit dont les caractéristiques ont été définies par l'entreprise ou le groupe d'entreprise qui en assure la vente au détail et qui est le propriétaire de la marque sous laquelle il est vendu »2 .

Bien que cette définition permette de clarifier le concept de MDD, son évolution démontre qu'il existe en réalité plusieurs types de MDD. Celles-ci recouvrent en effet une réalité hétérogène et des enjeux différents en fonction de leur politique de marquage : Les marques enseignes, signées du nom de l'enseigne, sont perçues par les consommateurs comme des produits de qualité comparable aux marques nationales (commercialisées par les industriels), mais vendues à des prix inférieurs (de 15 à 25 % moins cher). Les marques propres sont plus autonomes, portent un nom distinct de l'enseigne et développent essentiellement une offre originale et innovante apportant « de la valeur ajoutée et de la différenciation » [START_REF] Binninger | Les fondements psychologiques et relationnels des marques de distributeurs dans la distribution alimentaire[END_REF]. Les marques premier prix (ou marques économiques) sont des marques de première génération qui ont principalement construit leur stratégie et leur légitimité autour d'un discours économique et consumériste. La promesse d'une marque premier prix est donc simple : garantir, dans un magasin donné pour une catégorie de produits donnée, le prix de vente le plus bas comparativement à toutes les autres MDD référencées par les distributeurs. Elles renvoient généralement à des produits fonctionnels à forte rotation avec un packaging basique.

Le choix de notre étude s'est porté sur la perception de cette dernière catégorie de MDD. Ce sont en effet celles qui souffrent le plus comparativement aux marques propres et aux marques enseignes mais qui, paradoxalement, ont reçu le moins d'attention dans la littérature. Elles sont, en effet, soit exclues des études au profit des marques enseignes et/ou des marques propres [START_REF] Belaid | Les motivations d'achat et les leviers pour redynamiser l'offre des marques de distributeurs coeur de gamme[END_REF], soit incluses dans les travaux génériques sur la MDD, notamment les études anglo-saxonnes qui ne différencient pas les différents types de MDD [START_REF] Manikandan | Store brand and perceived risk on private label brand attitude[END_REF].

Cadrage théorique de l'étude : les transgressions de marque positives. Les transgressions de marques sont définies comme étant "un acte de violation des règles implicites ou explicites guidant la performance et l'évaluation de la relation consommateur-marque" (Aaker et al. 2004 ;[START_REF] Khamitov | A systematic review of brand transgression, service failure recovery and product-harm crisis: integration and guiding insights[END_REF]. Si une littérature étendue existe à leur sujet en marketing, les transgressions de marques demeurent employées majoritairement pour rendre compte d'un acte répréhensible d'ordre moral, éthique ou légal de la part des entreprises et/ou ayant des conséquences plutôt négatives sur les consommateurs, groupes d'individus, entreprises et/ou la société. Or, une transgression telle que conceptualisée dans les sciences humaines peut également avoir une dimension positive. Elle offre, par exemple, des opportunités de renouveau, d'interrogations des normes et des habitudes (Lefrançois, Changeur et Balech, 2022) à travers "des moments d'effervescence collective" (Durkheim, 1893) qui empêchent les sociétés de stagner [START_REF] Jenks | Transgression[END_REF].

En marketing, si certains travaux illustrent cet emploi positif de la transgression notamment en lien avec le progrès, l'innovation, l'opportunité et le futur (i.e.: [START_REF] Sarpong | Cultivating strategic foresight in practise: A relational perspective[END_REF]Barone et Jewell, 2013) ou reconnaissent certaines conséquences positives suite à la transgression d'une marque à l'exemple de la redynamisation de la relation à la marque (Aaker et al., 2004), les transgressions de marque positives restent largement sous-explorées dans la discipline. Pour cette raison, nous nous intéressons spécifiquement à la notion même de transgression de marque positive dans le cadre de cette recherche, c'est-à-dire aux cas pour lesquels la transgression est abordée en admettant qu'elle puisse (aussi) être positive en soi et dans ses conséquences.

Ainsi, nous considérons le fait pour une marque premier prix de proposer un packaging qui génère des associations de "meilleure qualité" du fait de caractéristiques extrinsèques connotées en ce sens comme une transgression de marque positive. La transgression réside ici dans le fait d'aller au-delà des normes et codes habituellement dévolus aux packagings d'une marque premier prix, ce qui peut constituer une innovation, un renouveau et susciter des émotions positives -telles que la surprise, le ravissement, le contentement, l'envie -chez les consommateurs. Ce processus demeure toutefois subordonné à la perception de meilleure qualité du packaging par les consommateurs sans pour autant remettre en question le positionnement de ces MDD par rapport aux autres. Il peut relever de différents mécanismes psychologiques, i.e.: la dissonance cognitive 3 [START_REF] Festinger | A Theory of Cognitive Dissonance[END_REF], l'incongruence 4 [START_REF] Maille | Congruence perçue par le consommateur: vers une clarification du concept, de sa formation et de sa mesure[END_REF][START_REF] Heckler | The role of expectancy and relevancy in memory for verbal and visual information: What is incongruency[END_REF]) ou encore la disconfirmation5 [START_REF] Maille | Congruence perçue par le consommateur: vers une clarification du concept, de sa formation et de sa mesure[END_REF].

Le packaging : vecteur de communication et rôle de réassurance quant à la qualité du produit.

Le packaging est souvent utilisé par les consommateurs pour prendre une décision ou développer une attitude particulière envers un produit ou une marque. C'est aussi le principal vecteur de communication de la marque et du produit en magasin. Ce processus correspond à la théorie du signal [START_REF] Olson | Cue Utilization in the Quality Perception Process[END_REF]. Appliquée au contexte de consommation, cette dernière considère que le consommateur, qui n'a accès qu'à une quantité limitée et restreinte d'informations sur un produit, s'appuie sur les signaux ou les indices émis -ici par l'enseigne -pour évaluer les produits et limiter le risque perçu [START_REF] Bezançon | Comment les distributeurs peuvent-ils réduire le risque perçu pour un achat d'occasion sur Internet ? Analyse exploratoire et proposition d'un nouveau cadre théorique[END_REF]. Bien que les indices intrinsèques (produit) aient souvent des valeurs de confiance plus élevées que les indices extrinsèques (packaging par exemple), les indices intrinsèques peuvent être difficiles à évaluer lors d'un achat [START_REF] Steenis | Consumer response to packaging design: The role of packaging materials and graphics in sustainability perceptions and product evaluations[END_REF]. Les consommateurs accordent alors une plus grande importance aux signaux extrinsèques tels que les packagings [START_REF] Richardson | Extrinsic and Intrinsic Cue Effects on Perceptions of Store Brand Quality[END_REF][START_REF] Underwood | Packaging communication: attentional effects of product imagery[END_REF]Zeithaml, 1988) qui apparaissent particulièrement importants lorsque le risque perçu est élevé ou lorsque la valeur prédictive d'un produit est faible [START_REF] Richardson | Extrinsic and Intrinsic Cue Effects on Perceptions of Store Brand Quality[END_REF]. Tel est le cas de la marque premier prix [START_REF] Lacoeuilhe | Marques de distributeurs et publicités comparatives directes des prix : des effets à différencier selon les types de MDD et les catégories de produits[END_REF][START_REF] Kadekova | The impact of packaging on consumer behavior in the private label market -the case of Slovak consumers under 25 years of age[END_REF].

Le packaging peut être décrit sur le plan de l'expression (signifiant) et le plan du contenu (signifié) [START_REF] Dano | Packaging: une approche sémiotique[END_REF]. Le plan de l'expression est composé d'éléments tangibles relevant de conceptions structurelles (forme, taille, texture…), graphiques (couleur, dactylographie…) et textuelles (informations sur le produit, contenu nutritionnel, DLC…). Ces caractéristiques peuvent servir d'indices au consommateur sur la qualité des produits et ainsi affecter la façon dont ils les évaluent et les choisissent [START_REF] Magnier | Communicating packaging eco-friendliness: An exploration of consumers' perceptions of eco-designed packaging[END_REF][START_REF] Diallo | Le comportement du consommateur face aux marques de distributeur au Brésil. Une étude qualitative[END_REF][START_REF] Magnier | Consumer reactions to sustainable packaging: The interplay of visual appearance, verbal claim and environmental concern[END_REF][START_REF] Van Rompay | Product Packaging Metaphors: Effects of Ambiguity and Explanatory Information on Consumer Appreciation and Brand Perception[END_REF]. Ils peuvent également avoir une influence directe sur les associations fonctionnelles (croyances de la marque) et symboliques (sentiments envers la marque, personnalité de la marque) de l'image de marque [START_REF] Pantin-Sohier | L'influence du packaging sur les associations fonctionnelles et symboliques de l'image de marque[END_REF]. Le plan du contenu correspond davantage à ce qui est exprimé, signifié et donc intangible. Le packaging peut, en effet, créer du sens non-matériel et imagé lorsqu'il est décrit comme discours, c'est-à-dire lorsqu'il répond à une logique de communication [START_REF] Dano | Packaging: une approche sémiotique[END_REF].

En comparaison avec les signaux des marques nationales, les consommateurs vont avoir tendance à percevoir les marques premier prix comme étant de moins bonne qualité [START_REF] Diallo | Le comportement du consommateur face aux marques de distributeur au Brésil. Une étude qualitative[END_REF]. Les signaux tels que le bas prix, l'absence de notoriété et de publicité pèsent sur la perception des MDD [START_REF] Diallo | Le comportement du consommateur face aux marques de distributeur au Brésil. Une étude qualitative[END_REF]. Ces perceptions peuvent également être favorisées par l'utilisation d'un packaging très sobre et/ou d'apparence bon marché et l'absence d'une image attractive [START_REF] Richardson | Extrinsic and Intrinsic Cue Effects on Perceptions of Store Brand Quality[END_REF]. Par exemple, certains résultats de tests organoleptiques MN vs MDD, indiquent que des marques nationales peuvent être mieux évaluées en tests identifiés, alors que les résultats à l'aveugle indiquent à l'inverse une amélioration de l'évaluation de la MDD en termes de qualité gustative. Les MDD sont désavantagées par leur image mais aussi par leur packaging, même lorsque le produit est considéré comme meilleur ou aussi bon gustativement [START_REF] Diallo | Le comportement du consommateur face aux marques de distributeur au Brésil. Une étude qualitative[END_REF].

L'importance de la fonction de communication du packaging, notamment en GMS n'est plus à démontrer, que ce soit sur la marque, les caractéristiques du produit ou son positionnement. Vecteur d'image, le packaging provoque également un effet de halo. Par exemple, à contenu identique, des études ont démontré qu'en fonction de la couleur et de la forme du packaging, les individus jugent différemment le goût des produits alimentaires (Becker et al., 2011).

Méthodologie de la recherche

Objectifs de la recherche. Afin de comprendre comment les consommateurs percevraient et appréhenderaient un packaging de marque premier prix s'il transgressait les normes en véhiculant un signal de meilleure qualité, il convient de s'intéresser, dans un premier temps, à la manière dont les consommateurs perçoivent le packaging des produits de marque premier prix, notamment au regard de la qualité perçue des produits. Pour ce faire, notre premier objectif empirique sera (1) d'identifier les caractéristiques extrinsèques d'un packaging de marque premier prix ainsi que leur importance dans la perception du positionnement "entrée de gamme". Leur connaissance (i.e.: formes, couleurs, symboles) est centrale dans notre étude puisqu'elle nous permettra d'identifier celles à privilégier et sur lesquelles s'appuyer pour permettre à un packaging de marque premier prix de véhiculer une image plus qualitative tout en conservant son positionnement "entrée de gamme".

Dans la seconde étape de notre étude, nous nous intéresserons plus en détail aux signifiants à mobiliser afin d'engendrer une perception de qualité d'une marque premier prix chez les consommateurs. Le second objectif empirique sera donc (2) de déterminer, pour les caractéristiques extrinsèques les plus centrales, les signifiants à favoriser pour qu'un packaging de marque premier prix véhicule une image plus qualitative tout en conservant son positionnement "entrée de gamme".

Enfin, nous nous pencherons sur la manière dont la transgression des normes et codes d'un packaging de marque premier prix affecte la perception du consommateur à l'égard dudit produit. Ainsi, notre dernier objectif empirique sera de (3) relever les éventuelles dissonances cognitives, incongruences et/ou disconfirmation causées par la présence de signifiants véhiculant un signal de meilleure qualité sur un packaging de marque premier prix.

Recueil et analyse des données.

Puisqu'il existe peu d'éléments dans la littérature quant à la perception des marques premier prix et que les recherches sur les transgressions de marque positives sont très éparses, une étude qualitative exploratoire s'impose.

La première étape de cette étude sera réalisée au moyen de la technique projective du collage. Cette technique d'élicitation de connaissances non-verbales et implicites consiste à demander aux consommateurs d'exprimer, entre autres, leurs idées à propos d'une marque en combinant différents matériaux, formes, couleurs ou images afin de créer une nouvelle composition [START_REF] Koll | Multi-method research on consumer-brand associations: Comparing free associations, storytelling, and collages: Consumer-Brand Associations[END_REF]. En favorisant l'activation de processus cognitifs chez les consommateurs, elle leur permet de révéler "des connaissances implicites ou inconscientes ainsi que de nouvelles associations inattendues avec la marque" [START_REF] Davis | Arts-based representation in qualitative research: Collage as a contextualizing analytic strategy[END_REF]. Cette première phase de collecte sera suivie d'entretiens semi-directifs auprès des mêmes participants afin de renforcer la pertinence de nos interprétations et d'appréhender les associations cette fois-ci explicites des consommateurs. Ils seront également l'occasion de poursuivre l'exploration de la perception des marques premier prix chez les consommateurs en les relançant, au besoin, quant à leurs caractéristiques extrinsèques définitoires et à l'importance de ces dernières.

Par la suite, nous nous attacherons à identifier les signifiants de la transgression ainsi que les signifiants à privilégier pour permettre à un packaging de marque premier prix de véhiculer une image plus qualitative en recourant à nouveau à la technique du collage suivis d'entretiens semi-directifs avec les mêmes répondants. Ces derniers entretiens nous permettront également d'explorer la manière dont la transgression des normes et codes d'un packaging de marques premier prix affecte la perception du consommateur à l'égard dudit produit par le repérage d'éventuelles dissonances cognitives, incongruences et/ou disconfirmations dans le discours des répondants.

L'analyse des données issues des collages s'appuiera sur l'élaboration d'une grille de codage pour guider nos interprétations. Nous accorderons une attention particulière aux différences, écarts et décalages entre les collages réalisés pour la marque premier prix et ceux portant sur la marque premier prix opérant une transgression de marque positive. En effet, ces derniers peuvent révéler les mécanismes associés à la perception des transgressions de marque positives par les consommateurs. Un des enjeux de l'interprétation sera alors de déterminer comment ces dissonances cognitives, incongruences et/ou disconfirmations sont perçues et si elles le sont plutôt positivement ou négativement.

Les données issues des entretiens semi-directifs seront quant à elles analysées conjointement au moyen du logiciel libre d'analyse de textes et de tableaux de données Iramuteq6 -qui propose un ensemble de traitements et d'outils pour l'aide à la description et à l'analyse de corpus textuels [START_REF] Loubère | Documentation IRaMuTeQ 0.6 alpha 3 version 0.1[END_REF] -ainsi que par une analyse thématique manuelle pour affiner notre interprétation.

Résultats attendus

Au terme de cette étude, nous serons en mesure de présenter les caractéristiques extrinsèques d'un packaging de marque premier prix qui puisse transmettre un message de qualité par sa conception structurelle, graphique et textuelle tout en respectant son positionnement "entrée de gamme".

Ce résultat sera soutenu par la connaissance des caractéristiques définitoires d'un packaging de marque premier prix et de l'importance de ces dernières. En outre, ces caractéristiques conditionnent en partie le positionnement "entrée de gamme" de ces marques. Leur connaissance constitue donc un enjeu tant pour les praticiens du marketing qu'en termes de contributions théoriques.

Aussi, cette recherche nous permettra d'acquérir des clés de compréhension quant à la manière dont les consommateurs perçoivent et appréhendent une marque premier prix qui s'inscrit dans la transgression de marque positive et qui, dans notre cas, sont celles dont les packagings transgressent les normes et codes qui leur sont habituellement dévolus.

Conclusion : apports et discussions

Ce travail contribue à la littérature marketing portant sur les marques premier prix ainsi que les transgressions de marque positives. En effet, peu de recherches sont réellement consacrées à ce type de marque, ces dernières étant souvent étudiées telles des marques de distributeurs dans un contexte francophone et n'ayant pas d'équivalent conceptuel dans la littérature anglo-saxonne.

Les transgressions de marques quant à elles font majoritairement l'objet d'études au sein desquelles elles ont des incidences négatives. Or, une transgression n'est ni (que) positive, ni (que) négative (Lefrançois, Changeur et Balech, 2022) et ses conséquences n'ont pas nécessairement d'externalités (que) négatives pour les parties transgressées [START_REF] Tsarenko | Reclaiming the Future: Understanding Customer Forgiveness of Service Transgressions[END_REF][START_REF] Khamitov | A systematic review of brand transgression, service failure recovery and product-harm crisis: integration and guiding insights[END_REF]. Mobiliser les transgressions de marque dans une visée positive demeure une démarche marginale en marketing dans laquelle cette étude entend s'insérer.

Nos résultats devraient également permettre de proposer des recommandations opérationnelles quant à la création de packagings de marques premier prix "équilibrés" qui soient en mesure de véhiculer une plus grande qualité perçue tout en respectant le positionnement "entrée de gamme".

Ces recommandations seront accompagnées de pistes de réflexions quant à la gestion des mécanismes associés à la perception des transgressions de marque positives (i.e.: dissonances cognitives, incongruences et/ou disconfirmations) chez les consommateurs, cette dernière étant provoquée par la transgression des normes et codes du packaging de marques premier prix. L'ensemble de ces pistes et recommandations a pour objectif de contribuer à la relance de ces dernières.

Cette étude comporte plusieurs limites liées, pour la plupart, à notre distance au terrain. En effet, l'étude empirique n'est pas encore réalisée. Par ailleurs, une autre considération émerge ; les normes relatives au packaging de marques premier prix étant profondément intériorisées par les consommateurs, ces derniers n'auraient-ils pas l'impression d'être trompés quant à la qualité intrinsèque du produit ? Comment prendre en compte le risque d'une perception de "quality washing" ainsi que le risque de cannibalisation des marques enseignes ? Jusqu'où la transgression peut-elle aller pour rester positive et favoriser le développement des MDD ?

Références bibliographiques

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  When good brands do bad. Journal of Consumer Research 31(1). Cary: Oxford Univ Press Inc: 1-16. DOI: 10.1086/383419. Barone MJ and Jewell RD (2013) The Innovator's License: A Latitude to Deviate from Category Norms. Journal of Marketing 77(1): 120-134. DOI: 10.1509/jm.10.0145. Becker L, van Rompay TJL, Schifferstein HNJ, et al. (2011) Tough package, strong taste: The influence of packaging design on taste impressions and product evaluations. Food Quality and Preference 22(1): 17-23. DOI: 10.1016/j.foodqual.2010.06.007.

Rapport LSA

: https://www.lsa-conso.fr/les-mdd-en-repli-de-3-7,382928

Loi n°2001-420 du 15 mai 2001 relative aux nouvelles régulations économiques, dites loi "NRE" : https://www.economie.gouv.fr/cepc/recommandation-ndeg-20-2-relative-un-guide-de-bonnes-pratiques-en-matie re-de-contrats-portant#n1

Écart perçu entre l'évaluation d'une marque et les attentes relatives à sa performance ou à celle d'une catégorie de produit.[START_REF] Maille | Congruence perçue par le consommateur: vers une clarification du concept, de sa formation et de sa mesure[END_REF].4 Relève du caractère non-pertinent et inattendu d'une association de différentes entités.3 "Sentiment d'inconfort psychologique, causé par deux éléments cognitifs discordants, et plongeant l'individu dans un état qui le motive à réduire ce sentiment inconfortable."[START_REF] Festinger | A Theory of Cognitive Dissonance[END_REF].

Iramuteq propose des méthodes statistiques (le calcul de spécificités, l'analyse factorielle et la classification), la visualisation de données textuelles (ex.: nuage de mots) et l'analyse de réseaux de mots par une analyse de similitudes(Baril et Garnier, 2015).