Guillaume Chomicki Fls
email: guillaume.chomicki@gmail.com

Luc P R Bidel

William J Baker Fls

Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans)

Keywords:

Mangrove species have evolved specialized structures, such as pneumatophores, to supply oxygen to the roots, but, in Nypa fruticans, the only mangrove palm, no such structure has been reported. This study aimed to determine the adaptations of N. fruticans to the mangal habitat with special reference to the air-supplying structure. Following senescence, the rachis is abscised at the zone of junction with the leaf base. Simultaneously, lenticels develop so that, when abscission is completed, a network of mature lenticels covers the leaf base. Expansigenous aerenchyma with increasing porosity towards the stem junction occurs in the leaf base. The first two root branching orders present a subero-lignified rhizodermis and exodermis, and the cortex consists of schizo-lysigenous aerenchyma with wide lacuna, limiting radial oxygen loss and facilitating longitudinal oxygen transport to living tissues. Lifespan estimation suggests that leaf bases can live for up to 4 years following abscission, ensuring the persistence of aeration structures. This study provides structural evidence indicating that N. fruticans has evolved a unique type of air-supplying structure in the mangal habitat.

INTRODUCTION

The success of mangrove species in waterlogged, and therefore anoxic and highly reduced, environments is classically attributed to the remarkable morphological adaptations of their root systems [START_REF] Scholander | Gas exchange in the roots of mangroves[END_REF][START_REF] Tomlinson | The botany of mangroves[END_REF]. These typically aerial root adaptations include pneumatophores [e.g. Avicennia marina (Forsk.) Vierh.], adventitious aerial roots that can emerge ectopically from high branches, such as in the red mangle (Rhizophora mangle L.), or form a cluster at the base of the trunk, known as stilt roots, such as in Rhizophora stylosa Griff, knee roots [e.g. Bruguiera gymnorrhiza (L.) Lamk.], buttress roots, such as those of Heritiera littoralis Aiton, or sinuous buttresses, so-called plank roots, of Xylocarpus granatum Ridl. [START_REF] Saenger | Morphological, anatomical and reproductive adaptations of Australian mangroves[END_REF][START_REF] Tomlinson | The botany of mangroves[END_REF]. All of these structures possess high densities of lenticels, which enable gas transfer whilst preventing water entry [START_REF] Tomlinson | The botany of mangroves[END_REF]. In mangrove species, it has long been assumed that such adaptive root systems enable oxygen transport to drowned tissues, hence ensuring aerobic metabolism in an anaerobic environment [START_REF] Scholander | Gas exchange in the roots of mangroves[END_REF][START_REF] Saenger | Morphological, anatomical and reproductive adaptations of Australian mangroves[END_REF][START_REF] Tomlinson | The botany of mangroves[END_REF].

Beyond the morphological adaptations of mangrove root systems, the key anatomical trait that enables tolerance to inundation and soil anoxia is the formation of aerenchyma with interconnected air channel systems throughout the plant. Consistently, an increase in tissue porosity and the formation of air channels are pivotal to increase the rate of oxygen diffusion in plant tissues [START_REF] Arber | Water plants: a study of aquatic angiosperms[END_REF][START_REF]Aeration in higher plants[END_REF]. Aerenchyma types fall into three main categories according to the mode of development: lysigeny, schizogeny and expansigeny [START_REF] Seago | A re-examination of the root cortex in wetland flowering plants with respect to aerenchyma[END_REF]. In lysigenous aerenchyma, the air lacunae arise from cell lysis and collapse, whereas, in schizogenous aerenchyma, cell separation of adjacent cell layers occurs, resulting in the joining of intercellular spaces into lacunae. Expansigeny is somewhat different from these two processes in that it involves the enlargement of intercellular spaces by cell division and expansion, but not by cell death, collapse or separation [START_REF] Seago | A re-examination of the root cortex in wetland flowering plants with respect to aerenchyma[END_REF].

Aerenchyma structure and development have been described in detail for several mangrove species, including Rhizophora mangle [START_REF] Gill | part of the species name or a missing reference? 4 Author: is (Purnobasuki and Suzuki[END_REF] and Avicennia marina (Purnobasuki and Suzuki, 2005). Moreover, in mangrove species, the pattern of oxygenation of the root system is dependent upon tides, with oxygen concentration peaking at low tides [START_REF] Scholander | Gas exchange in the roots of mangroves[END_REF][START_REF] Allaway | Gas space and oxygen exchange in roots of Avicennia marina (Forssk.) Vierh. var. australasica (Walp.) Moldenke ex NC Duke, the grey mangrove[END_REF].

Nypa fruticans Wurmb. is the only extant mangrove palm, and is distributed from India and Sri Lanka in the west through South-East Asia to Australia and the Solomon Islands [START_REF] Dransfield | Genera palmarum[END_REF]. Nypa Steck is a monotypic genus that arose as an early diverging lineage near the base of the palm phylogeny [START_REF] Asmussen | A new subfamily classification of the palm family (Arecaceae): evidence from plastid DNA phylogeny[END_REF][START_REF] Baker | Complete generic-level phylogenetic analyses of palms (Arecaceae) with comparisons of supertree and supermatrix approaches[END_REF], dated at 93.5 Mya [START_REF] Baker | Global biogeography and diversification of palms sheds light on the evolution of tropical lineages. I. Historical biogeography[END_REF].

Nypa has an extensive fossil record dating back to the upper Cretaceous (Maastrichtian) [START_REF] Tralau | The genus Nypa van Wurmb[END_REF][START_REF] Morley | Origin and evolution of tropical rain forests[END_REF][START_REF] Gee | The mangrove palm Nypa in the geologic past of the New World[END_REF][START_REF] Harley | A summary of fossil records for Arecaceae[END_REF][START_REF] Dransfield | Genera palmarum[END_REF][START_REF] Gomez-Navarro | Palms (Arecaceae) from a Paleocene rainforest of northern Colombia[END_REF], with occurrences reported from far outside its modern range, e.g. in the Americas, Europe and Africa. Recent palaeobotanical data indicate that extinct Nypa spp. were also found in waterlogged environments and that changes towards a drier climate in the late Eocene-early Miocene coincided with a dramatic decline in the distribution of Nypa [START_REF] Rull | Middle Eocene mangroves and vegetation changes in the Maracaibo Basin, Venezuela[END_REF][START_REF] Harley | A summary of fossil records for Arecaceae[END_REF][START_REF] Gomez-Navarro | Palms (Arecaceae) from a Paleocene rainforest of northern Colombia[END_REF]. Ancient records of Nypa coupled with swamp palaeoenvironments are used as a marker of the mangrove biota by palaeontologists (Gee, 2007). This suggests that the mangrove habit, and therefore the adaptation to the mangal habitat, is synapomorphic for the genus and not a recent adaptation in N. fruticans.

Nypa fruticans possesses an unusual habit for a mangrove plant (Fig. 1). In contrast with eudicot mangrove trees and shrubs, which have an orthotropic shoot system, N. fruticans has a plagiotropic stem that branches in a dichotomous manner, which, in turn, allows vegetative colonization [START_REF] Tomlinson | The shoot apex of Nypa fruticans and its dichotomous branching in the nypa palm[END_REF][START_REF] Tomlinson | The botany of mangroves[END_REF]Fig. 1). One remarkable adaptation of Nypa to the mangal habitat is the viviparous seedlings which germinate following seed maturation, before being shed from the fruiting head that terminates the inflorescence [START_REF] Tomlinson | The shoot apex of Nypa fruticans and its dichotomous branching in the nypa palm[END_REF], Fig. 1C). As a result of the plagiotropic habit of Nypa and tides, its stem is often immersed, the leaves being the only emergent part of the plant (Fig. 1). Nypa does not produce breathing roots like many other mangrove species, including some palm species living as mangal associates in wet habitats, which develop thin pneumatophores [START_REF] Tomlinson | The botany of mangroves[END_REF]. Thus, the airsupplying structures should be the leaves, as they are the only emergent part of the plant. Tomlinson (1995: 105) hypothesized that Nypa leaves play the role of a 'giant pneumatophore', based on their spongy texture and that of the rhizome ground tissue, and further suggested that this role may continue in the leaf base, noting that they break at an apparently similar position.

In this study, we explore the role of the Nypa leaf in the mangrove habit. We show that leaves of N. fruticans follow a distinctive developmental path, whereby the distal part of older leaves abscises, leaving behind persistent leaf bases that have attributes of pneumatophore-like aeration structures. This indicates that N. fruticans has evolved an air-supplying structure that is unique among mangrove species.

MATERIAL AND METHODS

PLANT MATERIAL

Plant material was collected from a mature specimen of N. fruticans growing at the Montgomery Botanical Center, Miami, FL, USA. The specimen was planted in 1982 (accession number 82473B). Additional root and leaf material was collected at the Royal Botanic Gardens, Kew, UK (accession number 2007-1564).

ANATOMY, STAINING AND MICROSCOPY

All anatomical sections were hand-cut apart from the lenticel sections in Figure 7, which are microtome sections. Staining for lignin was performed with a 5% w/v phloroglucinol solution (dissolved in ethanol) for 30 s, followed by concentrated hydrochloric acid (HCl) for 30 s. To detect suberin and cutin, we used a solution of 5% w/v Sudan IV in ethanol. Light microscopy (LM) was performed using a Leica DM LB100 microscope equipped with a Nikon Coolpix 4500 camera. For stereomicroscopy (for Fig. 7C only), we used a Leica KL300, and images were acquired with the same Nikon Coolpix 4500 camera. Epifluorescence microscopy was carried out on a Nikon epifluorescence microscope eclipse E600 fitted to a Nikon [START_REF] Liu | A laccase-like phenoloxidase is correlated with lignin biosynthesis in Zinnia elegans stem tissues[END_REF]. A Nikon B2-A filter (excitation spectrum, 450-480 nm) was used on diphenylboric acid 2-aminoethyl ester (DPBA)-stained slides to seek flavonoid distribution in tissues; yellow-gold or yellow-green fluorescence is associated with flavonoids (typically quercetin and kaempferol, respectively) [START_REF] Sheahan | Flavonoid-specific staining in Arabidopsis thaliana[END_REF].

IMAGE ANALYSIS AND POROSITY MEASUREMENTS

Image analysis, cell and lacunae measurements and aerenchyma area measurements were performed on imageJ (http://rsb.info.nih.gov/ij). Porosity was estimated from transverse sections of the rachis and leaf base. The porosity of the leaf base and rachis was determined by the quantification of aerenchyma lacunae over the total area [START_REF] Purnobasuki | Aerenchyma formation and porosity in root of a mangrove plant, Sonneratia alba (Lythraceae)[END_REF]. For each of the three positions in the leaf axis, the total area was determined for three cross-sections per position and the area of each lacuna was determined for each cross-section with the 'polygon selec- tion' and 'measure' tools of imageJ. The percentage of porosity was obtained as follows: porosity (%) = 100 × (area of air spaces/total cross-sectional area) [START_REF]Aeration in higher plants[END_REF][START_REF] Maricle | Aerenchyma development and oxygen transport in the estuarine cordgrasses Spartina alterniflora and S. anglica[END_REF][START_REF] Visser | Measurement of porosity in very small samples of plant tissue[END_REF].

LEAF BASE LIFESPAN ESTIMATION

With the hypothesis that the leaf base of Nypa fulfils an oxygenation role, it was pivotal to evaluate the leaf base lifespan. The leaf base lifespan is the sum of the whole leaf lifespan and post-abscission lifespan. [START_REF] Tomlinson | The structural biology of palms[END_REF] provided equations for the calculation of the leaf lifespan. The continuous growth of palms establishes that the lifespan of a single leaf A can be obtained from the product of the plastochrone interval P (i.e. the inverse of the number of leaves produced per year) and the total leaf number n, A = Pn [START_REF] Tomlinson | The structural biology of palms[END_REF]. The total leaf number is expressed as the sum of the exposed L e and unexposed L u (still enclosed in the crown) leaves, and can generally be estimated by means of observation as the number of exposed and unexposed leaves is similar, hence n = L u + Le ∼ 2Le [START_REF] Tomlinson | The structural biology of palms[END_REF], although this assumption is not always met [START_REF] Dalrymple | The relationship between the number of expanded and developing leaves in shoot apices of palms[END_REF]. To obtain the lifespan of the leaf bases, the equation should be modified so that the number of leaf bases n lb corresponds to the number of exposed leaves L e plus the number of unexposed leaves Lu, equivalent to L e, plus the number of living leaf bases post-abscission B abs, i.e. nlb = 2Le + Babs. Therefore, the leaf base lifespan is obtained from the equation A = Pn lb, that is A = P(2Le + Babs). Le and Babs were directly measured independently in five different shoots on one specimen (Table 1). The plastochrone interval P, however, requires longer times to be estimated accurately and was therefore taken from the literature. Plastochrone intervals for Nypa measured in wild populations varied from 3.04 ± 0.8 [START_REF] Fong | Studies on the population structure, growth dynamics and importance of nipa palm (Nypa fruticans Wurmb[END_REF] to 2.0 [START_REF] Rozainah | A demographic study of a mangrove palm, Nypa fruticans[END_REF]) leaves per year. Therefore, the leaf base lifespan A was calculated for values of P = 1/2, P = 1/2.5 and P = 1/3. The lifespan of the leaf bases post-abscission (A LBabs) was obtained using the equation A LBabs = P(Babs). The dif-ferent plastochrone intervals probably account for the error range because of the difference in the unexposed versus exposed leaves. Moreover, the lifespan of the post-abscission leaf base is independent of this parameter. A summary of the parameters measured and used for leaf lifespan evaluation is provided in Table 1.

RESULTS

LEAF ABSCISSION IN N. FRUTICANS

Leaves of N. fruticans can be > 7 m long [START_REF] Tomlinson | The shoot apex of Nypa fruticans and its dichotomous branching in the nypa palm[END_REF][START_REF] Tomlinson | The botany of mangroves[END_REF]. They consist of a wide (25-40 cm) leaf sheath or leaf base and a long rachis (6-8 m) in which reduplicate leaflets are inserted. The leaf sheath is open and has an adaxial groove, forming a welldefined leaf base that is separated from the rachis by a short petiolar transition zone. Leaves that subtend a dichotomy enclose two shoots and, as a result, possess two grooves (Fig. 1D). Abscission occurs at the transition zone between the leaf base and the rachis (Fig. 2A).

The abscission process starts with a distal to proximal senescence of the rachis and of leaflets, which stops just before the leaf base. The observation of mature Nypa specimens suggests that the first step in abscission is mechanical and consists of the folding of the rachis at the transition zone with the leaf base, just above the adaxial groove (Fig. 2A). A plot of diameter against leaf axis length reveals a large variation in diameter in the leaf base (35.7 cm m -1 ), but a small variation (1.4 cm m -1 ) in the rachis (Fig. 2C). To gain further insights into the mechanism of abscission, leaves undergoing abscission were sectioned longitudinally. The intact leaf base aerenchyma is separated by a clear abscission zone that is followed by a zone of degradation (Fig. 2D). Importantly, cells in the zone of abscission and in the adjacent degraded zone have thick-walled, nonlignified cell walls (Fig. 2E-G). In contrast, cells in the adjacent aerenchyma of the leaf base and the rachis are characterized by thin cell walls (Fig. 2D,E). Furthermore, cells in the abscission zone are small and often present in rows of three to four cells, indicating recent division (Fig. 2H). Cells distally adjacent to the abscission zone (Deg in Fig. 2E) exhibit substantial cell wall hydrolysis signs (Fig. 2F,G), with string-like detachment of cellulose microfibrils (Fig. 2I) and glomerular agglomeration of degraded cell walls (Fig. 2J), suggesting high activity of cell wall hydrolases, such as cellulase. Once the rachis is completely removed from the leaf base, the exposed surface of the zone ultimately becomes cutinized (Fig. 2B). After completion of the abscission process, the leaf base remains as a living appendage.

LEAF BASE LIFESPAN IN NYPA

Following rachis abscission, leaf bases do not senesce, but persist for a long time. The leaf base lifespan in Nypa was evaluated using an equation modified from [START_REF] Tomlinson | The structural biology of palms[END_REF] who used palm canopy parameters (see Material and Methods). Total leaf base lifespan (before and after abscission) was estimated to be over 8 years on average (Fig. 3A), with the rachis living from 3.0 to 5.5 years according to the plastochrone interval (Fig. 3B). The leaf base lifespan after abscission was found to be 4.1, 3.3 and 2.7 years, on average, for the respective plastochrone intervals used (Fig. 3C). [START_REF] Fong | Studies on the population structure, growth dynamics and importance of nipa palm (Nypa fruticans Wurmb[END_REF] calculated that the leaf lifespan in Nypa is 5.5 years in wild populations in Malaysia, providing a cross-validation of our results.

LENTICELS RESULT FROM TRANSIENT MERISTEMATIC ACTIVITY BELOW THE STOMATA IN LEAF

BASES OF NYPA Stomata are present on the abaxial epidermis of the leaf base (which represents most of the surface, the adaxial epidermis being restricted to the groove) and rachis at a density of c. 20 cm -2 . Leaf bases (most notably after abscission) possess a network of lenticels, the density of which is equivalent to the stomatal density. The examination of the leaf base epidermis at different ages reveals that lenticels develop in the place of existing stomata (Fig. 4A-D).

On the leaf base, stomata stay functional for only a short time after leaf initiation (Fig. 4A). Cutin rapidly accumulates around the stomata and guard cells, the latter probably accumulating other phenolic substances, resulting in the maintenance of stomata in the open state (Fig. 4B). Subsequently, stomata become longitudinally split by the appearing lenticel (Fig. 4C). Finally, the lenticel develops and all stomatal traces disappear (Fig. 4D). Although this process occurs all along the leaf axis (leaf base and rachis), mature lenticels (Fig. 4D) do not occur on the distal part of the rachis as it is abscised before they can develop.

To understand the mechanisms underlying lenticel formation, anatomical sections were performed at different stages of lenticel development (i.e. for differently aged leaf bases). Cork anatomy consists of an epidermis with four underlying cell layers of tanninrich cells, termed tannin idioblasts (TI), followed by about four layers of more or less round cells that have a suberized and lignified thick cell wall with a small, tannin-rich lumen, and are referred to as tannin brachysclereids (TB) (Fig. 5A).

Longitudinal and transverse sections in young stomata show rows of aligned cells suggestive of a meristematic zone (Fig. 5B-D) and, in turn, indicate that lenticel development starts at an early stage. The meristematic activity emanates from the parenchymatous cells under each stoma, and the pattern of the disposition of rows of three of four cells in Figure 5B-D indicates that each parenchymatous cell gives rise to three or four daughter cells, and hence has a limited meristematic potential. Following division, the cells differentiate centripetally into TIs and cells that resemble dicot phellem cells, termed phellem-like cells (Fig. 5E,F).

The alternation of phellem-like tissue and TIs uncovers a transient mode of functioning (Fig. 5F). That is, once a definite set of parenchyma cells has divided and produced TIs and phellem-like tissue, another set of parenchymatous cells inner to the first set divides and produces a new TI and phellem-like tissue. This results in an alternation of TIs and phellem-like cells in mature lenticels (Fig. 5F). A lenticel showing such organization, i.e. with more than one cycle of parenchyma differentiation, is termed secondary.

EXPANSIGENOUS AERENCHYMA PROVIDES AN AIR PATHWAY FROM LENTICELS TOWARDS THE ROOTS

The ground tissue of the leaf axis in Nypa consists of aerenchyma (Fig. 6). The air canals or lacunae of the aerenchyma are established along a gradient of diameter; the more proximal, the wider is the lacuna (Fig. 6A-F), with a marked increase in lacuna diameter towards the leaf base (Fig. 6G). Increased lacuna density and increased lacuna diameter result in a dramatic porosity increase towards the leaf base (Fig. 6I).

To determine the origin of the difference in lacuna diameter along the leaf axis, lacunae were observed at different positions along the leaf base/rachis axis using serial transverse sections. Distinct types of lacuna are identified according to the number of cells that border each lacuna and the degree of elongation of these cells (Fig. 6K-O). Transitional stages with cells in division were found in young leaf bases (Fig. 6P,Q), suggesting that these stages form a developmental series. The number of cells bordering a lacuna increases gradually towards the leaf base (Fig. 6J). However, cell length increases only in the leaf base (Fig. 6H), rather than gradually along the leaf axis.

A longitudinal section revealed that air lacunae form closed air pockets (Fig. 6R). These air pockets are separated by a single-celled layer in the leaf base (Fig. 6O), and this increases to over three cell layers in the rachis. The lacunae are interconnected by a pattern of cell wall pitting on the walls of certain cells (Fig. 6R,S).

ROOT ARCHITECTURE AND ANATOMY IN NYPA

Nypa roots are present at high density in the first 10 cm of substrate. In N. fruticans, the root system presents an architecture characterized by three branching orders in the architectural system of [START_REF] Hallé | Tropical trees and forests, an architectural analysis[END_REF] (Fig. 7A). In contrast with previous studies, all three axis orders were examined, and it appears that the different orders vary substantially in their anatomy and potential functionality (Fig. 7).

The first order (AX1) is about 0.5 cm in diameter and presents a thick rhizodermis with slightly lignified outer walls, and the subsequent four or five cell layers constitute the exodermis which is suberized and interspersed with tanniferous cells (Fig. 7C,G). The lignified rhizodermis is followed by four or five suberized exodermal cell layers that contain interspersed tanniferous cells (arrow in Fig. 7G). The second axis (AX2) is 2-3 mm in diameter and has a layer of highly tanniferous and probably suberized cells that follows the rhizodermis, and three non-lignified, parenchymatous cell layers which are followed by lignified cells less dense than the other (Fig. 7H). The identification of the dark brown cells as tanniferous is in accordance with [START_REF] Seubert | Root anatomy of palms III. Ceroxyloideae, Nypoideae, Phytelephantoideae[END_REF], who reported highly tanniferous cells in the first three cell layers of AX1 roots in N. fruticans. Total delayed reiteration (reproduction of the total root architectural system) occurs, at least in cases of traumatism (Fig. 7A, black arrows; white arrow shows a partial reiteration). Aerenchyma type and development are equivalent in AX1 and AX2, with the exception that the ratio

Colour online, B&W in print

bs_bs_query occupied by aerenchyma diminishes in AX2 as ∼15 cell layers of parenchyma follow the exodermis, by contrast with AX1 (Fig. 7C,D), thus reducing the porosity in AX2. Aerenchyma development shows features of schizogenous development (i.e. cell separation) (Fig. 7I,J) and lysigenous development (i.e. cell lysis and collapse) (Fig. 7D,K). Lysigeny directly follows schizogenous cell separation (Fig. 7I,J), resulting in an apparently entirely lysigenous aerenchyma. A peculiar cell type in the diffuse inner cortex is not affected by either schizogeny or lysigeny, and is characterized by larger cells that are connected to many more cells than those of the diffuse inner cortex which forms aligned cell rows (Fig. 7L,M). These 'scaffolding cells' apparently help to maintain the root structure in AX1 and AX2 by keeping lacunae together (Fig. 7L). Furthermore, these cells are concentrated towards both the surface tissues and the stele to prevent aerenchyma formation in these zones (Fig. 7M). In contrast, aerenchyma in the third and last root order (AX3) is non-lysigenous and non-schizogenous and is reduced to small intercellular spaces (Fig. 7E,F).

DISCUSSION

THE ABSCISSION TYPE IN NYPA [START_REF] Tomlinson | The structural biology of palms[END_REF] emphasized that leaf abscission, despite being a developmentally and ecologically important phenomenon, is a neglected area of palm biology. A major dichotomy was, however, recognized early with self-cleaning versus non-self-cleaning palm trunks, as related to the sheath structure (La [START_REF] Floresta | Sul meccanismo della caduta delle foglie nelle palme[END_REF][START_REF] Schoute | Sur la fissure médiane de la gaine foliaire de quelques palmiers[END_REF][START_REF] Tomlinson | The structural biology of palms[END_REF]. Clearly, the abscission pattern exhibited by N. fruticans does not fall into these categories because abscission concerns only the rachis and not the whole leaf.

The presence of non-lignified fibres and of larger thick-walled non-lignified cells in the abscission zone (Fig. 2E-G) is a crucial determinant of the abscission mechanism. This cellulose-rich ground tissue becomes, at the time of abscission, easy to degrade by the activation of cell wall-degrading enzymes, such as cellulase and polygalacturonase, which have long been known to play a key role in abscission in other species, including the palm Elaeis guineensis Jacq. [START_REF] Horton | Senescence, abscission and cellulase activity in Phaseolus vulgaris[END_REF][START_REF] Lewis | Synthesis of cellulase during abscission of Phaseolus vulgaris leaf explants[END_REF][START_REF] Reid | Cellulase and abscission in the red kidney bean (Phaseolus vulgaris)[END_REF][START_REF] Riov | A polygalacturonase from Citrus leaf explants role in abscission[END_REF][START_REF] Addicott | Abscission[END_REF][START_REF] Bonghi | Cellulase and polygalacturonase involvement in the abscission of leaf and fruit explants of peach[END_REF][START_REF] Henderson | The study of a monocotyledon abscission zone using microscopic, chemical, enzymatic and solid state 13 C CP/MAS NMR analyses[END_REF]. Cells with degraded cell walls, as well as mucilage found in the abscission region (data not shown), clearly indicate that rachis abscission in Nypa is an active process. The development of a distinctive abscission zone, as evidenced by anatomy and recently divided cells, is consistent with this hypothesis.

Cell wall degradation in the abscission zone, resulting in weakening, associated with the physiognomy of the Nypa leaf, would then induce the folding of the leaf by external factors such as wind, which, in turn, would exert a mechanical action facilitating the abscission, notably by helping fibres embedded in the ground tissue break.

The evolution of such a unique abscission mechanism dependent on both the mechanics of the leaf physiognomy and the expression of cell wall hydrolases in the transition zone suggests a functional selection pressure for the remaining leaf base.

TANNIN ACCUMULATION AND LEAF LIFESPAN

A striking feature of leaf bases in N. fruticans is the change in colour of the internal parenchymatous tissues as they age (Fig. 8). These compounds are The occurrence and protective role of tannins has been widely reported in roots, leaves and bark of mangrove species [START_REF] Kimura | Tannins in mangrove tree roots and their role in the root environment[END_REF][START_REF] Tomlinson | The botany of mangroves[END_REF][START_REF] Hernes | Tannin diagenesis in mangrove leaves from a tropical estuary: a novel molecular approach[END_REF][START_REF] Zhang | Condensed tannins from mangrove species Kandelia candel and Rhizophora mangle and their antioxidant activity[END_REF]. As antioxidants, tannins have been shown to play protective functions against bacterial and fungal pathogens [START_REF] Smith | Increasing the oxidative stress response allows Escherichia coli to overcome inhibitory effects of condensed tannins[END_REF][START_REF] Smith | Effect of condensed tannins on bacterial diversity and metabolic activity in the rat gastrointestinal tract[END_REF][START_REF] Ishida | Influence of tannins from Stryphnodendron adstringens on growth and virulence factors of Candida albicans[END_REF] and in protecting roots from reduced and acidic soil conditions by association with ferric ions [START_REF] Kimura | Tannins in mangrove tree roots and their role in the root environment[END_REF]. The generalized accumulation of tannins in leaf base ground tissue is consistent with a protective role in the leaf base.

A recent study evaluating the corrosion inhibition potential of tannin solutions of N. fruticans indicated that the leaf base and inflorescence stem are the most proficient against corrosion, and therefore the most tannin-rich [START_REF] Satar | Corrosion inhibition of aluminium by using nipah (Nypa fruticans) extract solution in hydrochloric acid (HCl) media[END_REF]. Tannin induction and subsequent gradual accumulation is a marker of leaf base aging (Fig. 8). The heterotrophic and semiimmersed condition of leaf bases of Nypa after abscission makes them sensitive to pathogens. Therefore, this process of tannin accumulation is probably a protective mechanism against such pathogens. Thus, tannin accumulation probably plays a role in the long lifespan of Nypa leaf bases.

AERENCHYMA DEVELOPMENT IN NYPA

Following the taxonomy of [START_REF] Seago | A re-examination of the root cortex in wetland flowering plants with respect to aerenchyma[END_REF], three types of aerenchyma can be identified in N. fruticans: honeycomb expansigenous aerenchyma in the leaf base and the proximal part of the rachis; schizo-lysigenous aerenchyma in the first-and second-order roots; and radial expansigenous aerenchyma in the third-order root. [START_REF] Drabble | On the anatomy of roots of palms[END_REF] described lysigenous aerenchyma in the roots of Areca L. and Howea Becc. Generally, it has been argued that aerenchyma development, which occurs in the roots of many palm species, is of lysigenous origin [START_REF] Tomlinson | The structural biology of palms[END_REF][START_REF] Tomlinson | The anatomy of palms: Arecaceae-Palmae[END_REF], although [START_REF] Tomlinson | The structural biology of palms[END_REF] speculated on the existence of schizogeny in palm roots. Although other studies have claimed to demonstrate schizogeny in palm roots, none has provided microscopic evidence (e.g. [START_REF] Mahabale | Studies on palms: part IV-anatomy of palm roots[END_REF][START_REF] Seubert | Root anatomy of palms III. Ceroxyloideae, Nypoideae, Phytelephantoideae[END_REF]. Therefore, this is the first unequivocal evidence for this type of aerenchyma in the family. Schizogeny appeared to be particularly promoted by intercellular spaces of the parenchymatous cells (i.e. radial expansigeny), which must be present at an early stage in root development, facilitating cell separation; this relation was also noticed by [START_REF] Seubert | Root anatomy of palms III. Ceroxyloideae, Nypoideae, Phytelephantoideae[END_REF].

The developmental gradient of honeycomb expansigenous aerenchyma present in leaf bases of Nypa provides an efficient way of increasing porosity towards the stem junction. This type of aerenchyma is also present in the stem of palm species such as Archontophoenix alexandrae (F.Muell.) H.Wendl. & Drude and Roystonea regia (Kunth) O.F.Cook, where it provides a mechanism for stem enlargement in the absence of secondary growth [START_REF] Tomlinson | The anatomy of palms: Arecaceae-Palmae[END_REF]. The disproportional physiognomy of the leaf base in comparison with the rachis, which is thought to play a role in the abscission process, is a consequence of the expansigenous aerenchyma gradient.

AIR PATHWAY FROM THE LEAF BASE TO THE ROOTS

In addition to the role of the leaf base as an aeration structure in N. fruticans, this study provides a preliminary account for the air pathway. Oxygen entry into the leaf base of Nypa is thought to be greatly facilitated by hypertrophic lenticels, which have long been known to enhance air entry into tissues in mangrove and non-mangrove woody plants [START_REF] Scholander | Gas exchange in the roots of mangroves[END_REF][START_REF]Aeration in higher plants[END_REF]. Following air entry from lenticels, the interconnected lacuna provided by the expansigenous aerenchyma in the leaf base allows a conduction of the oxygen down to the junction of the stem. Although the stem was not studied here for practical reasons, it is known that the stem of Nypa is also aerenchymatous [START_REF] Tomlinson | The botany of mangroves[END_REF][START_REF] Tomlinson | The anatomy of palms: Arecaceae-Palmae[END_REF]. Following entry into the roots, oxygen is conducted in the schizo-lysigenous aerenchyma in the first two root orders (AX1 and AX2). The impermeable ligno-suberized rhizodermis and exodermal layers of AX1 and AX2 probably reduce radial oxygen loss, thus enhancing longitudinal oxygen transport to the third and last root order (AX3).

Quantification of the branching level of each root order revealed that the second branching order (AX2) is five-fold more branched than the first branching order (AX1), corresponding to a 1 : 2 : 10 ratio of the three branching orders (Fig. 7B) This 1 : 10 ratio of large over fine roots in Nypa is significant because it has been shown that fine roots consume much less oxygen than major roots [START_REF] Bidel | Mapping meristem respiration of Prunus persica (L.) Batsch seedlings: potential respiration of the meristems, O2 diffusional constraints and combined effects on root growth[END_REF]. Thus, the architecture of the root system in Nypa, with the 1 : 2 : 10 abundance of the three root branching orders, may reduce the oxygen demand of the flooded root system. This large number of fine roots certainly also produces a large surface to volume ratio, enhancing nutrient uptake. The absence of hydrophobic surface layers on the fine roots (AX3) certainly greatly enhances radial oxygen loss. This probably helps to create microaerobic oxidizing conditions that minimize phytotoxin entry, consistent with previous studies [START_REF] Armstrong | Phragmites australis: venturi-and humidity-induced pressure flows enhance rhizome aeration and rhizosphere oxidation[END_REF][START_REF] Youssef | Anatomical adaptive strategies to flooding and rhizosphere oxidation in mangrove seedlings[END_REF].

CONCLUSION

This study provides structural evidence for a new aeration structure of a mangrove species. Nypa leaves This will open up a panel down the right side of the document. The majority of tools you will use for annotating your proof will be in the Annotations section, pictured opposite. We've picked out some of these tools below:

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  2 G. CHOMICKI ET AL.© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013,

  document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133 camera Ds-Fi 1. A Nikon DAPI (4′,6-diamidino-2phenylindole) filter (excitation spectrum, 380-420 nm) was used to track lignin in tissues. Under this filter, bright blue-white fluorescence is attributed to lignin autofluorescence and blue autofluorescence depicts all other cell walls

Figure 1 .

 1 Figure 1. Nypa fruticans habit, specimen growing at the Montgomery Botanical Center, FL, USA, planted in 1982. A, Habit and general morphology of N. fruticans. B, Young inflorescence showing the pleonanthic habit (axillary inflorescences) of N. fruticans. C, Inflorescence. D, Young dichotomizing stem showing the two sister shoots and the subtending leaf with the two enclosing grooves. Scale bars: B, 15 cm; C, D, 10 cm.

  . (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

  Comment citer ce document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

Figure 2 .

 2 Figure 2. Abscission pattern in Nypa fruticans. A, First stage of abscission, involving the distal to proximal necrosis of the leaf to the abscission zone. White arrowhead points to the beginning of the groove. Black arrow shows abscission zone. B, Abscission scar in surface view. C, Leaf axis width plotted as a function of the leaf distance from the basal-most point (as shown by leaf diagram). D, Longitudinal section of the aerenchyma in the leaf base. E, Longitudinal section in the abscission zone. F, Details of the cells that are above the abscission zone (in the Deg zone in E). G, Young non-lignified fibres in the abscission zone (frame in E). H, Recently divided cells in the abscission zone. Top panel represent a bright-field image, bottom panel represents a merged with DAPI (4′,6-diamidino-2-phenylindole) image. Arrowheads point to the cell walls parallel to the division plane. I, J, Cell wall hydrolysis during abscission in the Deg zone shown in E. Arrowheads show the degraded cell wall and cellulose agglomeration. Scale bars: A, 10 cm; B, 1.2 cm; D, 60 μm; E, 200 μm; F, 40 μm; G, 30 μm; H, I, 20 μm; J, 15 μm. Abbreviations: Abs, abscission zone; Aer, aerenchyma; Deg, degraded cells.

14 bs_bs_query

 14 Colour online, B&W in print bs_bs_query Comment citer ce document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

Figure 3 .

 3 Figure 3. Evaluation of leaf base lifespan. A, Total leaf base lifespan (ALB) (before and after abscission). B, Rachis lifespan (AR). C, Post-abscission leaf base lifespan (ALBabs). Each data point represents one shoot. For each plastochrone interval modelled, the same dataset with the number of exposed leaves (Le) and the number of post-abscission leaf bases recorded from five independent shoots of a 27-year-old Nypa specimen [82473B, Montgomery Botanical Center (MBC)] was used.

  Comment citer ce document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

Figure 4 .

 4 Figure 4. Emergence of lenticels from stomata on Nypa leaf bases. A, Stomata on a leaf base of a young leaf. B, Guard cells accumulate cutin and are 'frozen' open on a slightly older leaf base. C, In a young leaf base, a lenticel forms in the place of a stoma. The location of the stoma is clearly visible. D, Young lenticel on an adult leaf base. Scale bars: A, 25 μm; B, 300 μm; C, 75 μm; D, 1.5 mm.

  . (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

Figure 5 .

 5 Figure 5. Transient meristematic activation underneath stomata underpins lenticel development on fruticans leaf base. A, Anatomy of the 'cork' (longitudinal section). B, Longitudinal section of a stoma on a young leaf base. C, Close-up of the frame shown in B pointing out two clusters of recently divided cells. D, Transverse stomatal section through a stoma. E, Transverse section of a young lenticel. F, Transverse section of a mature lenticel. Microscopy type and staining: A, D, epifluorescence with a B2A filter and diphenylboric acid 2-aminoethyl ester (DPBA) staining; B, C, epifluorescence with a 4′,6-diamidino-2-phenylindole (DAPI) filter; E, F, light microscopy with Sudan IV staining. Scale bars: A, 40 μm; B, 80 μm; C, 30 μm; D, 30 μm; E, 350 μm; F, 200 μm. Abbreviations: Ep, epidermis; Fib, fiber; MZ, meristematic zone; Par, parenchyma; PhL1 and PhL2, phellem-like cells 1 and 2, respectively; St, stoma; TB, tannin brachysclereid; TI, tannin idioblast; TI1 and 2, primary and secondary tannin idioblast, respectively.

Figure 6 .

 6 Figure 6. Acropetal gradient of expansigenous aerenchyma in Nypa leaf base. A, B, Rachis transverse section; arrow points to a lacuna. C, D, Transition zone transections. E, F, Leaf base transection (position 3 in the leaf scheme). G, Lacuna diameter in the zones of the leaf axis shown in the scheme. H, Cell length of the aerenchyma in the zones shown in the scheme, n = 77, 88 and 128 for positions 1, 2 and 3, respectively. All cell measurements were made from transverse sections of the leaf axis. I, Porosity (volume of air spaces) in the three positions studied, n = 3. J, Distribution of cell number per lacuna in transverse sections in the rachis, transition zone and base of the leaf axis. K-O, Developmental anatomy of the aerenchyma. Arrowhead in K points to the nascent lacuna. P, Q, Cell division occurring in aerenchyma cells. R, S, Longitudinal section in the leaf base showing cell wall pitting on the side of the lacunae. Microscopy type and staining: A, C, E, K-O, R, S, light microscopy (LM) with phloroglucinol-HCl staining; B, D, F, P, Q, epifluorescence with a 4′,6-diamidino-2-phenylindole (DAPI) filter. Scale bars: A, B, 200 μm; C, D, 130 μm; E, F, 150 μm; K-O, 40 μm; P, Q, 50 μm; R, S, 50 μm.

14 bs_bs_query

 14 Colour online, B&W in print bs_bs_query Comment citer ce document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

Figure 7 .

 7 Figure 7. Nypa root architecture and anatomy. A, General architecture of Nypa fruticans roots. Black arrows indicate reiteration of AX1. White arrow indicates fourth root order, showing reiteration of AX1. B, Branching capacity of each root order as evaluated by the number of root branches per centimetre. C, Anatomy of the first root order (AX1). D, Anatomy of the second root order (AX2). E, Anatomy of the third root order (AX3). F, Detail of the anatomy of AX3. Arrow points to an intercellular space (radial expansigenous aerenchyma). G, Anatomy of the surface layers in AX1. Arrow points to a tannin idioblast. H, Anatomy of the surface layers in AX2. I, Detail of the aerenchyma in AX1, showing a schizogenous leading end (frame). Arrow shows an intercellular space. J, Close-up of the frame illustrated in I showing a schizogenizing end. Arrow indicates an intercellular space. K, Lysigeny in AX1. Arrow points to cells in the process of lysis. L, Scaffolding cells in AX1 lysigenous aerenchyma (arrows). M, Concentration of scaffolding cells (arrows) at the outer end of the aerenchyma. Double arrow indicates a cell file in the aerenchyma. Microscopy type and staining: C, D, E, light microscopy (LM) with phloroglucinol-HCl staining; G, H, co-stained with phloroglucinol-HCl and Sudan IV; I-M, epifluorescence with a 4′,6-diamidino-2-phenylindole (DAPI) filter. Scale bars: A, 1 cm; C, 200 mm; D, 200 μm; E, F, 120 μm; G, H, 70 μm; I-M, 50 μm. Abbreviations: Exo, exodermis; LA, lacuna; LF, lignified fibres; Rhi, rhizodermis; Tan, tanniniferous layer.

14 bs_bs_query

 14 Colour online, B&W in print bs_bs_query Comment citer ce document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133

Figure 8 .

 8 Figure 8. Tannin accumulation in the leaf base of Nypa fruticans. The leaf bases were collected from the same shoot, A being the youngest (distal-most) and C the oldest (basal-most). The scheme at the top left illustrates the position of the leaf bases A, B and C.

14 bs_bs_query

 14 Colour online, B&W in print bs_bs_query Comment citer ce document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133 soluble and dark red, and are most likely tannins.

  12 G. CHOMICKI ET AL. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013,



  document : Chomicki, G. (Auteur de correspondance), Bidel, L., Baker, W. J., Jay-Allemand, C. (2014). Palm snorkelling: leaf bases as aeration structures in the mangrove palm (Nypa fruticans). Botanical Journal of the Linnean Society, 174 (2), 257-270. DOI : 10.1111/boj.12133 USING e-ANNOTATION TOOLS FOR ELECTRONIC PROOF CORRECTION Required software to e-Annotate PDFs: Adobe Acrobat Professional or Adobe Reader (version 8.0 or above). (Note that this document uses screenshots from Adobe Reader X) The latest version of Acrobat Reader can be downloaded for free at: http://get.adobe.com/reader/ Once you have Acrobat Reader open on your computer, click on the Comment tab at the right of the toolbar: 1. Replace (Ins) Toolfor replacing text. Strikes a line through text and opens up a text box where replacement text can be entered. How to use it  Highlight a word or sentence.  Click on the Replace (Ins) icon in the Annotations section. Type the replacement text into the blue box that appears.

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Table 1 .

 1 Parameters measured for the estimation of the leaf base lifespan in Nypa fruticans

	4 1b s_bs_query
	2b s_bs_query
	3b s_bs_query	Shoot number (n = 5)	Number of living leaves (Le)	Number of leaf base (Babs)
	4b s_bs_query
	5b s_bs_query	1	5	7
	6b s_bs_query	2	4	7
	7b s_bs_query	3	6	6
	8b s_bs_query	4	6	8
	9b s_bs_query	5	5	1 3
	10b s_bs_query	Average	5	7.5
	11b s_bs_query
	12b s_bs_query
	13b s_bs_query			56b s_bs_query
	14b s_bs_query			57b s_bs_query
	15b s_bs_query			58b s_bs_query
	16b s_bs_query			59b s_bs_query
	17b s_bs_query			60b s_bs_query
	18b s_bs_query			61b s_bs_query 62b s_bs_query
	19b s_bs_query
	20b s_bs_query			63b s_bs_query
	21b s_bs_query 22b s_bs_query			64b s_bs_query
	23b s_bs_query			65b s_bs_query
	24b s_bs_query			66b s_bs_query
	25b s_bs_query			67b s_bs_query
	26b s_bs_query			68b s_bs_query
	27b s_bs_query			69b s_bs_query
	28b s_bs_query			70b s_bs_query
	29b s_bs_query			71b s_bs_query
	30b s_bs_query			72b s_bs_query
	31b s_bs_query			73b s_bs_query
	32b s_bs_query			74b s_bs_query
	33b s_bs_query			75b s_bs_query
	34b s_bs_query			76b s_bs_query
	35b s_bs_query			77b s_bs_query
	36b s_bs_query			78b s_bs_query
	37b s_bs_query			79b s_bs_query
	38b s_bs_query			80b s_bs_query
	39b s_bs_query			81b s_bs_query
	40b s_bs_query			82b s_bs_query
	41b s_bs_query			83b s_bs_query
	42b s_bs_query			84b s_bs_query
	43b s_bs_query			85b s_bs_query
	44b s_bs_query			86b s_bs_query
	45b s_bs_query			87b s_bs_query
	46b s_bs_query			88b s_bs_query
	47b s_bs_query			89b s_bs_query
	48b s_bs_query			90b s_bs_query
	49b s_bs_query			91b s_bs_query
	50b s_bs_query			92b s_bs_query
	51b s_bs_query			93b s_bs_query
	52b s_bs_query			94b s_bs_query
	53b s_bs_query			95b s_bs_query
	54b s_bs_query			96b s_bs_query
	55b s_bs_query			97b s_bs_query

G. CHOMICKI ET AL. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, ••, ••-••

bs_bs_query

bs_bs_query

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ACKNOWLEDGEMENTS

We thank Paula Rudall and Jeremy Aroles for critical reading of the manuscript. The first author expresses his gratitude to P. B. Tomlinson, who not only proposed the hypothesis investigated in this study, but also provided the opportunity to investigate it. Patrick Griffith is acknowledged for permission and technical help to collect Nypa material at the Montgomery Botanical Center (MBC), Miami, FL, USA, and Larry Noblick for providing phenological data on N. fruticans growing at MBC. The National Botanical Tropical Gardens (NTBG) is thanked for a scholarship to G.C. in 2009. Two anonymous reviewers are thanked for comments on the manuscript. We wish to dedicate this paper to P. B. Tomlinson and his remarkable career in the structure of plants and, in particular, palms.

NYPA LEAF BASE FUNCTION 13 © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, ••, ••-•• 1b s_bs_query 2b s_bs_query 3b s_bs_query 4b s_bs_query 5b s_bs_query 6b s_bs_query 7b s_bs_query 8b s_bs_query 9b s_bs_query 10b s_bs_query 11b s_bs_query 12b s_bs_query 13b s_bs_query 14b s_bs_query 15b s_bs_query 16b s_bs_query 17b s_bs_query 18b s_bs_query 19b s_bs_query 20b s_bs_query 21b s_bs_query 22b s_bs_query 23b s_bs_query 24b s_bs_query 25b s_bs_query 26b s_bs_query 27b s_bs_query 28b s_bs_query 29b s_bs_query 30b s_bs_query 31b s_bs_query 32b s_bs_query 33b s_bs_query 34b s_bs_query 35b s_bs_query 36b s_bs_query 37b s_bs_query 38b s_bs_query 39b s_bs_query 40b s_bs_query 41b s_bs_query 42b s_bs_query 43b s_bs_query 44b s_bs_query 45b s_bs_query 46b s_bs_query 47b s_bs_query 48b s_bs_query 49b s_bs_query 50b s_bs_query 51b s_bs_query 52b s_bs_query 53b s_bs_query 54b s_bs_query 55b s_bs_query 56b s_bs_query 57b s_bs_query 58b s_bs_query 59b s_bs_query 60b s_bs_query 61b s_bs_query 62b s_bs_query 63b s_bs_query 64b s_bs_query 65b s_bs_query 66b s_bs_query 67b s_bs_query 68b s_bs_query 69b s_bs_query 70b s_bs_query 71b s_bs_query 72b s_bs_query 73b s_bs_query 74b s_bs_query 75b s_bs_query 76b s_bs_query 77b s_bs_query 78b s_bs_query 79b s_bs_query 80b s_bs_query 81b s_bs_query 82b s_bs_query 83b s_bs_query 84b s_bs_query 85b s_bs_query 86b s_bs_query 87b s_bs_query 88b s_bs_query 89b s_bs_query 90b s_bs_query 91b s_bs_query 92b s_bs_query 93b s_bs_query 94b s_bs_query 95b s_bs_query 96b s_bs_query 97b s_bs_query 98b s_bs_query 99b s_bs_query 100b s_bs_query 101b s_bs_query 102b s_bs_query 103b s_bs_query 104b s_bs_query 105b s_bs_query 106b s_bs_query 107b s_bs_query 108b s_bs_query 109b s_bs_query 110b s_bs_query 111b s_bs_query 112b s_bs_query 113b s_bs_query 14 G. CHOMICKI ET AL. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, ••, ••-•• 1b s_bs_query 2b s_bs_query 3b s_bs_query 4b s_bs_query 5b s_bs_query 6b s_bs_query 7b s_bs_query 8b s_bs_query 9b s_bs_query 10b s_bs_query 11b s_bs_query 12b s_bs_query 13b s_bs_query 14b s_bs_query 15b s_bs_query 16b s_bs_query 17b s_bs_query 18b s_bs_query 19b s_bs_query 20b s_bs_query 21b s_bs_query 22b s_bs_query 23b s_bs_query 24b s_bs_query 25b s_bs_query 26b s_bs_query 27b s_bs_query 28b s_bs_query 29b s_bs_query 30b s_bs_query 31b s_bs_query 32b s_bs_query 33b s_bs_query 34b s_bs_query 35b s_bs_query 36b s_bs_query 37b s_bs_query 38b s_bs_query 39b s_bs_query 40b s_bs_query 41b s_bs_query 42b s_bs_query 43b s_bs_query 44b s_bs_query 45b s_bs_query 46b s_bs_query 47b s_bs_query 48b s_bs_query 49b s_bs_query 50b s_bs_query 51b s_bs_query 52b s_bs_query 53b s_bs_query 54b s_bs_query 55b s_bs_query 56b s_bs_query 57b s_bs_query 58b s_bs_query 59b s_bs_query 60b s_bs_query 61b s_bs_query 62b s_bs_query 63b s_bs_query 64b s_bs_query 65b s_bs_query 66b s_bs_query 67b s_bs_query 68b s_bs_query 69b s_bs_query 70b s_bs_query 71b s_bs_query 72b s_bs_query 73b s_bs_query 74b s_bs_query 75b s_bs_query 76b s_bs_query 77b s_bs_query 78b s_bs_query 79b s_bs_query 80b s_bs_query 81b s_bs_query 82b s_bs_query 83b s_bs_query 84b s_bs_query 85b s_bs_query 86b s_bs_query 87b s_bs_query 88b s_bs_query 89b s_bs_query 90b s_bs_query 91b s_bs_query 92b s_bs_query 93b s_bs_query 94b s_bs_query 95b s_bs_query 96b s_bs_query 97b s_bs_query 98b s_bs_query 99b s_bs_query 100b s_bs_query 101b s_bs_query 102b s_bs_query 103b s_bs_query 104b s_bs_query

undergo a unique abscission process by which only the rachis is shed, leaving the leaf base in place.

A lenticel network develops on the leaf base whilst the rachis senesces. These hypertrophied lenticels connect to the aerenchyma network that occurs from the leaf base to the roots. Leaf bases remain alive for up to 4 years after abscission, perhaps aided by protection from tannins, ensuring that the aeration system remains functional for a long time. Further studies are needed to investigate the physiology of root oxygenation in N. fruticans.

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