Origin and development of stomatal microanatomy in two species ofEucalyptus

Summary Development of the stomata ofEucalyptus orbifolia (in which they are relatively superficial) andE. incrassata (in which they are deeply sunken) is described from light microscopy of thin sections of resin-embedded material. The envelope of the guard mother cell is retained intact while in the daughter cells (guard cells) the inner and outer thickenings are formed. The mother cell envelope may even remain discrete and intact during early stages of formation of the separation spaces, precursors of the future stomatal pore, between the thickenings. Remnants of the guard mother cell wall may be retained as parts of at least the inner stomatal ledges. Likewise, remnants of the wall which divides the mother cell persist on the maturing guard cells.Sudan III-positive materials, probably cutin, are removed from the cuticle over the mother cell soon after it is formed. The cuticle above the guard cell is finally perforated by enzymic attack forming, inE. incrassata, a large cavity outside the developing stoma into which the outer stomatal ledges grow as extensions of the upper guard cell walls.The termostiole is suggested for the aperture in the cuticle. The flanges of cuticle seen in section to bound it are termedostiolar ledges. The ostiolar ledges are to be distinguished from the outer stomatal ledges, which develop from the upper thickenings of the guard cell initials. The distinction is clear inE. incrassata (and other species with deeply sunken stomata) but not in mesophytic plants or species with superficial stomata such asE. orbifolia in which the outer stomatal ledges are fused with the cuticle.Growth of the outer stomatal ledges inE. incrassata involves transport of wall materials through an annular space, the equivalent of an ectocythode.The relevance of the observations to stomatal development in other genera is discussed.     

Scanning electron microscopy studies of cuticle micromorphology in Cycas L. (Cycadaceae)

Abstract

A scanning electron microscopy (SEM) study of Cycas cuticle characteristics was undertaken in order to expand our knowledge of microscopic characters not observable under light microscopy and to clarify unresolved affinitites among some species within the genus. Whole leaf and isolated cuticle specimens from the middle region of leaflets of greenhouse-grown plants of Cycas revoluta, Cycas rumphii, Cycas circinalis, Cycas media, and Cycas normanbyana were examined using SEM for interior and exterior features. Characteristics in common include hypostomy, hair bases on abaxial and adaxial surfaces, adaxial cells randomly arranged, adaxial exterior cuticle smooth, and stomata sunken to various degrees but stomatal pit always formed by two layers of epidermal cells. Stomatal complex is of the polyperigenous type. Stomata randomly dispersed and oriented, and except C. revoluta, are not contiguous. Stomata deeply sunken in C. revoluta, intermediate in C. rumphii and C. normanbyana, and less sunken in C. circinalis and C. media. Aperture between guard cells extends the entire stomatal length in C. rumphii and C. normanbyana, ～80% in C. circinalis and C. media, and ～50% in C. revoluta. Cuticular features of C. revoluta show the greatest difference from the other species in complex relief of exterior cuticle and interior cuticular structure of subsidiary cells; C. media and C. circinalis show close similarity to each other and their stomatal complex dimensions fall within the same unique cluster using principal component analysis under normalized variables. C. normanbyana and C. rumphii show the most similarity to each other in cuticular micromorphology. Stomatal complex dimensions of these two species fall into a second cluster that also includes C. revoluta. These data contrast with current taxonomy placing C. normanbyana synonymous to C. media.     

ULTRASTRUCTURE AND DEVELOPMENT OF THE INACTIVE STOMATA OF ANABASIS ARTICULATA (FORSK.) MOQ.

The guard cells of Anabasis articulata mature and senesce a short distance from the intercalary meristem in which they form. When the guard cells reach final size, their ultrastructure is similar to that of stomata of other plants. At this stage, they contain clearly definable, numerous mitochondrial profiles, chloroplasts with starch grains and plastoglobuli, active Golgi bodies, a large nucleus that stains deeply for chromatin and large vacuoles. During later stages of development the whole protoplasmic content becomes very dense, with myelin-like figures and crystals appearing in the vacuoles. The cell walls thicken considerably. This is especially true of the tangential walls, where the microfibrils of different lamellae vary in their orientation. It is suggested that as a result of these ultrastructural changes the guard cells lose the ability to move.     

INTRAMARGINAL VEINED LAURACEAE LEAVES FROM THE ALBIAN–CENOMANIAN OF CHARENTE-MARITIME (WESTERN FRANCE)

Abstract:  Eucalyptolaurus depreii gen. et sp. nov. is proposed for angiosperm leaves newly collected from uppermost Albian – lowermost Cenomanian of Charente-Maritime (western France). They consist of simple, narrow, elongate laminas with entire margins and intramarginal veins. The epidermal cells of adaxial cuticle shows small, rounded, blunt papillae outward that protrude inward and fuse together as rolls along and parallel to the margins, while the adaxial cuticle bears brachyparacytic stomatal apparatus that exhibit sunken guard cells and hair bases consisting of a thick-walled pore surrounded by radially arranged differentiated cells. Resin bodies occur inside the mesophyll. These characters closely resemble the lauroid taxa ' Myrtophyllum ' and Pandemophyllum from the Cenomanian of the Czech Republic and Dakota (USA) respectively. The narrow angle of basilaminar secondaries and the whole suite of features in the guard cells (sunken guard cells embedded into subsidiary cells and stomatal ledges) strongly support close affinity with the Lauraceae. From the Cenomanian lauraceous reproductive organs and their related leaves already showed high disparity and diversity. In addition they displayed a broad ecological range from freshwater floodplains to brackish swamps. This combined to high diversity of reproductive organs suggest ecological radiation of Lauraceae by the Cenomanian.     

琼岛杨和响叶杨叶结构的比较研究

琼岛杨(Populus qiongdaoensis T.Hong et P.Luo)是海南热带雨林中杨属一新种^[1],曾被误为响叶杨(P.adenopoda Maxim)本文试图从叶片的结构比较它们的异同,为区分这两个种提供比较形态学的依据。     

Micromorpho-Anatomical Examination of 2,4-D Phytotoxicity in Grapevine (Vitis vinifera L.) Leaves

The anatomical and micro-morphological alterations as induced by the auxinic herbicide, 2,4-D (2,4-dichlorophenoxy acetic acid) have not yet been elucidated for a commercially important fruit crop such as grapevine despite its super sensitivity to 2,4-D. Light and scanning electron microscopy techniques were employed to examine 2,4-D induced internal and external structural abnormalities in Merlot grapevines (Vitis vinifera L.). Healthy leaves were dorsiventrally flattened with well developed patterns of cellular structure and composition involving adaxial palisade parenchyma and abaxial spongy mesophyll. Dorsiventral variations in epidermal features involved large epidermal cells on the adaxial surface, and trichomes and stomata with turgid elliptical guard cells on the abaxial surface. The 2,4-D injured leaves were small and enated; the veins were fasciated with rugose bands of lamina existing between fasciated veins. The epidermal cells aggregated instead of being positioned coplanar to the epidermal plane. The adaxial elongated palisade parenchyma cells were transformed into an ovoid shape with intercellular spaces. An extensive development of replacement tissues took place on the abaxial surface wherein the stomata became roundish and were either raised or sunken with collapsed and cracked guard cells that developed abnormal outer stomatal ledges. These abnormalities are expected to severely perturb the vital functions of photosynthesis and transpiration ultimately leading to vine death attributable, at least in part, to the injured leaves.     

THE CUTICULAR ANATOMY OF FRENELOPSIS VARIANS FROM THE LOWER CRETACEOUS OF CENTRAL TEXAS

Stem fragments identified as Frenelopsis varions Fontaine have been found in the Lower Cretaceous (Albian) of central Texas. The cuticle is extremely thick and characterized by 5–6 subsidiary cells with papillae overarching the stomatal chamber. Guard cells are deeply sunken below the epidermis. Stomatal complexes are arranged in axial rows extending from the base of an internode to its apex. The rows of stomata continue into the sheathing leaf where the rows curve towards the leaf apex. The epidermis of F. varions was apparently long persistent and underwent prolonged growth. Axial rows of stomata are frequently disrupted resulting in a random pattern of stomata. A single, highly reduced, sheathing leaf is present at each node. The margin of the leaf has numerous unicellular trichomes and extends to form a slightly triangular blade.     

Isolation of genes predominantly expressed in guard cells and epidermal cells of Nicotiana glauca

Guard cells are specialized and metabolically active cells which arise during the differentiation of the epidermis. Using Nicotiana glauca epidermal peels as a source of purified guard cells, we have constructed a cDNA library from guard cell RNA. In order to isolate genes that are predominantly expressed in guard cells, we performed a differential screen of this library, comparing the hybridization of a radiolabeled cDNA probe synthesized from guard cell RNA to that from a mesophyll cell cDNA probe. Sixteen clones were isolated based on their greater level of hybridization with the guard cell probe. Of these, eight had high homology to lipid transfer protein (LTP), two were similar to glycine-rich protein (GRP), and one displayed high homology to proline-rich proteins from Arabidopsis thaliana (AtPRP2, AtPRP4) and from potato guard cells (GPP). Northern analysis confirmed that one or more NgLTP genes, NgGRP1, and NgGPP1 are all differentially expressed, with highest levels in guard cells, and low or undetectable levels in mesophyll cells and in roots. In addition, all are induced to some degree in drought-stressed guard cells. NgLTP and NgGRP1 expression was localized by in situ hybridization to the guard cells and pavement cells in the epidermis. NgGRP1 expression was also detected in cells of the vasculature. Genomic Southern analysis indicated that LTP is encoded by a family of highly similar genes in N. glauca. This work has identified members of a subset of epidermis- and guard cell-predominant genes, whose protein products are likely to contribute to the unique properties acquired by guard cells and pavement cells during differentiation.     

Taxonomic significance of leaf surface morphology in Aloe section Pictae (Xanthorrhoeaceae)

Leaf surface morphology was analysed in 32 species representing the maculate species complex (the poorly resolved section Pictae) in the genus Aloe (Xanthorrhoeaceae). Few comparative morphological data are available for the complex. Leaf surface and stomatal characters observed by scanning electron microscopy show taxonomically significant interspecific variation. Most species are characterized by irregularly outlined, four‐ to six‐sided epidermal cells, the periclinal walls of which are flat and embellished with micropapillae and the anticlinal walls of which are indicated by channels on the leaf surface. The outer stomatal pore is typically sunken or plane and surrounded by four lobes on the leaf surface that may overarch the epistomatal chamber. The guard cells have distinct outer and inner stomatal ledges. Two geographical groups, comprising southern and east African species, are distinguishable by their leaf surface morphology. These characters are diagnostic in A. ellenbeckii, A. prinslooi and A. suffulta and support changes in the delimitation of A. greatheadii, A. macrocarpa and A. swynnertonii. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 418–428.     

Endogenous Diurnal Rhythm in the Osmotic Surplus of the Guard Cells

The osmotic surplus of the guard cells —i.e., the difference between the guard cells’and epidermal cells’omotic value at incipient plasmolysis (Vicia Faba) —exhibits an endogenous diurnal-periodic variation that is synchronous with the endogenous diurnal periodicity in the movements of the guard cells. The osmotic surplus of the guard cells is found to arise and drop by changes not only in these cells, but also in the epidermal cells.     

Immuno-reactant to RhoA antibody co-localizes with cortical actin filaments in guard cells of open stomata inCommelina communis L.

Stomatal regulation is essential for the growth of land plants. Pairs of guard cells that delineate the stomata perceive stimuli and respond to acquire the optimum aperture. The actin cytoskeleton participates in signaling pathways of the guard cell (Kim et al., 1995; Eun and Lee, 1997; Hwang et al., 1997). To identify the upstream molecules that regulate actin dynamics in plant cells, we immunoblotted proteins extracted from leaves ofCommelina commuais L. with the RhoA antibody, and identified one band of 26KD from the epidermis. Using immunofluorescence microscopy, we examined the subcellular distribution of the immuno-reactant(s) in guard cells. When stomata were open under light, the organization of the immuno-reactant(s) resembled the radial arrangement of cortical actin filaments of guard cells. Double-labeling of the guard cells, using the RhoA and actin antibodies as primary antibodies, showed that the immuno-reactant(s) of the RhoA antibody and actin filaments co-localized in the cortex of illuminated guard cells. However, the pattern was not found in guard cells when stomata were closed under darkness or by ABA, conditions under which cortical actin proteins are disassembled in guard cells. From these observations, we can suggest the possible presence of a RhoA-like protein and its involvement in the organization of the actin cytoskeleton in guard cells.     

A light and electron microscopy study of the epidermis of Paphiopedilum spp. with emphasis on stomatal ultrastructure

Abstract Light and fluorescence microscopy studies indicated that chlorophyll was absent from the guard cells of the lady slipper orchids, Paphiopedilum insigne (Wall.) Pfitz, P. insigne (hybrid), P. venustum (Wall.) Pfitz and P. harrisseanum Hort. In the guard cells of P. aureum hyeanum Hort., however, very slight red fluorescence suggested that chlorophyll and hence chloroplasts were present. Ultrastructural studies of the lower epidermis of P. insigne (hybrid) confirmed the absence of chloroplasts in guard and epidermal cells although plastids of an unusual structure were found in these cells. In fully developed epidermal cells the plastids contained large amounts of a fibrous, possibly proteinaceous substance, spherical, lightly staining vesicles and an electron-dense material located in reticulate and non-reticulate regions. Additionally, latticed crystalline inclusions and plasto-globuli were occasionally observed in the epidermal cell plastids. In plastids of fully developed guard cells the fibrous material, starch and plastoglobuli were present. From the earliest stages of development of the epidermal tissue starch was present in both epidermal cell and guard cell plastids. At maturity, however, starch had accumulated to greater levels in the guard cell plastids and had entirely disappeared in the epidermal cell plastids. In differentiating epidermal tissue, plasmodesmata were found between neighbouring epidermal cells and between guard and epidermal cells. At maturity, plasmodesmata between guard and epidermal cells were not observed. Mitochondria were particularly abundant in guard cells. Large oil drops developed in guard and epidermal cells, being especially abundant in the former at maturity. Our results confirm the observations of Nelson & Mayo (1975) that certain lady slipper orchids possess functional stomata the guard cells of which do not contain chloroplasts.     

On the properties of fluorescing compounds in guard and epidermal cells of Allium cepa L.

Onion guard cells, in contrast to those of Vicia and Pisum, do not require an alkaline treatment in order to fluoresce. Fluorescing compounds of Allium cepa L. were characterized using in-vivo microspectrophotometry; furthermore, invitro chemical analysis for epidermal tissue, intact guard and epidermal cells, and isolated guard-cell protoplasts was performed. The emission intensity (_max 520 nm) decreased when intact onion guard cells were excited with 436 nm light, but increased (_max 470 nm) when excited at 365 nm. This photodecomposition at 436 nm is typical of flavins or flavoproteins whereas an increase in fluorescence intensity with excitation at 365 nm may be explained by the presence of other substances. The presence of flavins could not be unambiguously confirmed from these results. Indeed, the absorption spectra of the vacuolar area of guard cells did not show the peak at 445 nm which is characteristic for flavins. Furthermore, there was no decrease of absorption at the excitation wavelengths of 440 and 330 nm. Since spectral data indicate the presence at high amounts of flavonoids in guard and epidermal cells, this may reduce the sensitivity for the detection of flavins in guard cells. Using thin-layer chromatography and high-performance liquid chromatography together with hydrolytic procedures, flavonol glycosides with kaempferol and quercetin as aglycones substituted with sulphate and glucuronate were identified. Further studies on guard-cell metabolism should consider the presence of flavonoids in stomata of onion and other plants.Abbreviations GCP guard-cell protoplast - HPLC high-performance liquid chromatography - TLC thin-layer chromatography     

Microtubule reorganization accompanying preprophase band formation in guard mother cells ofAvena sativa L.

Summary In order to study developmental changes in microtubule organization attending the formation of a longitudinally oriented preprophase band, the guard mother cells ofAvena were examined using a new procedure for anti-tubulin immunocytochemistry on large epidermal segments. We found that the interphase band (IMB) of transverse cortical microtubules present in these cells following asymmetric division is replaced after subsidiary cell formation by mesh-like to radial microtubules that extend throughout the cytoplasm. Many of the Mts are also grouped in bundles. Gradually, this intermediate array is succeeded by longitudinal elements of the PPB. Thus, preprophase band formation is accompanied by a 90° shift in Mt orientation, with a radial arrangement serving as an intermediate stage. The micrographs are most consistent with the rearrangement of intact Mts, although changes in Mt assembly are possible as well. The role of the IMB in guard mother cells is also discussed.Abbreviations GMC guard mother cell - IMB interphase microtubule band - Mt microtubule - PPB preprophase band     

PHYSIOLOGICAL IMPLICATIONS OF VICIA FABA AND NICOTIANA TABACUM GUARD-CELL ULTRASTRUCTURE

The guard cells of Vicia faba and Nicotiana tabacum contain numerous mitochondria, elements of endoplasmic reticulum, spherosomes, and peroxisome-like microbodies. A full ribosomal complement appears in young but not in fully mature guard cells. Numerous small lipid droplets external to the plasmalemma were noted in mature Vicia guard cells. Chloroplasts were found in both epidermal and guard cells of both species. Full photosynthetic capacity was indicated by the grana fretwork of guard-cell chloroplasts. A specialized peripheral reticulum was observed in the guard-cell chloroplasts of Vicia. Plasmodesmata were observed in both walls between sister guard cells and between guard and epidermal cells. In the latter case plasmodesmata were found primarily in pit fields of transverse walls. It is postulated that the small volume of guard cells allows them an osmotic advantage over larger neighboring cells in generating turgor.     

AtALMT12 represents an R‐type anion channel required for stomatal movement in Arabidopsis guard cells

Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and anions from guard cells. Anion efflux from guard cells involves slow (S‐type) and rapid (R‐type) anion channels. Recently the SLAC1 gene has been shown to encode the slow, voltage‐independent anion channel component in guard cells. In contrast, the R‐type channel still awaits identification. Here, we show that AtALMT12, a member of the aluminum activated malate transporter family in Arabidopsis, represents a guard cell R‐type anion channel. AtALMT12 is highly expressed in guard cells and is targeted to the plasma membrane. Plants lacking AtALMT12 are impaired in dark‐ and CO₂‐induced stomatal closure, as well as in response to the drought‐stress hormone abscisic acid. Patch‐clamp studies on guard cell protoplasts isolated from atalmt12 mutants revealed reduced R‐type currents compared with wild‐type plants when malate is present in the bath media. Following expression of AtALMT12 in Xenopus oocytes, voltage‐dependent anion currents reminiscent to R‐type channels could be activated. In line with the features of the R‐type channel, the activity of heterologously expressed AtALMT12 depends on extracellular malate. Thereby this key metabolite and osmolite of guard cells shifts the threshold for voltage activation of AtALMT12 towards more hyperpolarized potentials. R‐Type channels, like voltage‐dependent cation channels in nerve cells, are capable of transiently depolarizing guard cells, and thus could trigger membrane potential oscillations, action potentials and initiate long‐term anion and K⁺ efflux via SLAC1 and GORK, respectively.     

On Cordaites neimengensis sp. nov from Lower Permian of Zhungeerqi,Inner Mongolia, China

The leaf cuticle of Cordaites neimengensis sp. nov was studied by light and scanning electron microscopy. The specimens were collected from kower Permian of Zhungeerqi, Inner Mongolia (Neimenggu), China. Comparing with other species of Cordaites, it was a new species of the genus, based on the structure of its epidermis. Cordaites neimengensis sp. nov (Pis. Ⅰ to Ⅲ; Text-fig.l,B) The specimen comprises two incomplete leaves over 16 cm in length. One is about 1.4 cm wide at the lower part and 0.3 cm wide at the upper part, with nearly 29 veins per cm and 3 to 5 interstitials. The width of the other leaf is about 7.5 cm at the lower part and 8.2 cm at the upper part with 25 veins per cm and 3 to 5 interstitials. Epidermis amphistomatic. Epidermal cells of upper cuticle aligned in longitudinal rows, nearly rectangular in shape, about 33.6 to 86.4 pm x 10.2 to 28. 8 pm in size. Stomatal apparatus consisting of 2 sunken guard cells surrounded by 2 lateral and 2 polar subsidiary cells. Stomata haplocheillic, about 56.2 pm x 45.5 pm in size, usually arranged in short chains, with one polar subsidiary cell (usually 23.1 to 25.4 pm wide, 34.1 to 39.2 pm long in size) shared with 2 consecutive stomata. The polar subsidiary cells round, oblong or rhomboid in shape. The guard cells reniform or bean-shaped, usually 9.7 to 11.6 pm wide, 23.4 to 29.1 pm long in size. Density and index of stomata about 18/mm2 and 3.2%, respectively. Epidermal cells of lower cuticle also nearly rectangular in shape, about 62.4 to 144 pm × 9.6 to 16.8 pm in size. Stomata on the lower cuticle, haplocheillic, 40.8 pm wide and 48 pm long in size, with a pair of sunken guard cells, which is bean-shaped and surrounded by 2 lateral and polar subsidiary cells. Stomata arranging in parallel bands, typically one, sometimes two. As for the latter, a single row of lateral subsidiary cells (9.2 to 14.4 pm wide, 33.6 to 62.4 pm long in size) is shared with 2 parallel rows of stomata and occasionally also in bands with two rows side by side. In view outside, small papillae on the outer periclinal wall as well as the lateral subsidiary cells. In view inside, some folds along the anticlinal wall but flat about the periclinal wall. Nonstomatic bands usually with 1 to 10 rectangular cell rows. Density and index of the stomata about 209/mm2 and 27.2 %, respectively. 1401%-type: 9342; locality: Heidaigou of Zhungeerqi; Inner Mongolia, North China; Age: Lower Pennian (Shanxi Formation).     

Microtubule dynamics are involved in stomatal movement ofVicia faba L.

Summary To obtain a full picture of microtubule (MT) behavior during the opening and closure of guard cells we have microinjected living guard cells ofVicia faba with fluorescent tubulin, examined fine detail by freeze shattering fixed cells, and used drug treatments to confirm aspects of MT dynamics. Cortical MTs in fully opened guard cells are transversely oriented from the ventral wall to the dorsal wall. When the stomatal aperture was decreased by darkness, these MTs became twisted and patched and broken down into diffuse fragments when stomata were closed. When the closed stomata were opened in response to light, the MTs in guard cells changed from the diffused, transitional pattern back to one in which MTs are transversely oriented from stomatal pore to dorsal wall. This observation indicates a linkage between these MT changes and stomatal movement. To confirm this, we used the MT-stabilizing agent taxol and the MT-depolymerizing herbicide oryzalin and observed their effects on the stomatal aperture and MT dynamics. Both drugs suppressed light-induced stomatal opening and dark-induced closure. MTs are known to be necessary for maintaining the static kidney shape of guard cells; the present data now show that the dynamic properties of polymeric tubulin accompany changes in shape with stomatal movement and may be functionally involved in stomatal movement.     

Ion channels in guard cells of Arabidopsis thaliana (L.) Heynh.

Despite the availability of many mutants for signal transduction, Arabidopsis thaliana guard cells have so far not been used in electrophysiological research. Problems with the isolation of epidermal strips and the small size of A. thaliana guard cells were often prohibiting. In the present study these difficulties were overcome and guard cells were impaled with double-barreled microelectrodes. Membrane-potential recordings were often stable for over half an hour and voltage-clamp measurements could be conducted. The guard cells were found to exhibit two states. The majority of the guard cells had depolarized membrane potentials, which were largely dependent on external K⁺ concentrations. Other cells displayed spontaneous transitions to a more hyperpolarized state, at which the free-running membrane potential (E_m) was not sensitive to the external K⁺ concentration. Two outward-rectifying conductances were identified in cells in the depolarized state. A slow outward-rectifying channel (s-ORC) had properties resembling the K⁺-selective ORC of Vicia faba guard cells (Blatt, 1988, J Membr Biol 102: 235–246). The activation and inactivation times and the activation potential, all depended on the reversal potential (E_rev) of the s-ORC conductance. The s-ORC was blocked by Ba²⁺ (K_1/2 = 0.3–1.3mM) and verapamil (K_1/2 = 15–20 μM). A second rapid outward-rectifying conductance (r-ORC) activated instantaneously upon stepping the voltage to positive values and was stimulated by Ba²⁺. Inward-rectifying channels (IRC) were only observed in cells in the hyperpolarized state. The activation time and activation potential of this channel were not sensitive to the external K⁺ concentration. The slow activation of the IRC (t_1/2 ≈ 0.5 s) and its negative activation potential (V_threshold = −155 mV) resemble the values found for the KAT1 channel expressed in Saccharomyces cerevisiae (Bertl et al., 1995, Proc Natl Acad Sci USA 92: 2701–2705). The results indicate that A. thaliana guard cells provide an excellent system for the study of signal transduction processes. Received: 28 March 1996 / Accepted: 11 November 1996     

Cuticle micromorphology of Saxegothaea (Podocarpaceae)

The cuticle micromorphology of the leaves of the monospecific genus Saxegothaea (Podocarpaceae) was studied by scanning electron microscopy. The external and internal features of the adaxial and abaxial surfaces were characterized. The leaves are hypostomatic. The external adaxial cuticle is rugose with irregular ridges and shallow trench‐like structures that do not correspond to any feature of the inner cuticle surface. The external abaxial cuticle has densely crowded stomata arranged in two bands. The stomata are sunken with pronounced, interrupted Florin rings. Stomatal plugs were not observed. Internally, the adaxial epidermal cells are usually rectangular to square; the abaxial epidermal cells are mainly restricted to the midrib and margins and narrowly rectangular; any among the stomata are irregularly shaped. The stomata are nearly all in direct contact. They show unusual features, including an extra pair of cuticular flanges between the guard cell flanges and those of the lateral subsidiary cells, and ‘bridges’ of lateral subsidiary cell tissue extending polewards above the polar extensions to unite with those at their tips. Neither of these features has been reported previously in Podocarpaceae. The results are discussed in the light of recent phylogenetic studies. It is concluded that, despite its unique cuticular features, Saxegothaea should continue to be regarded as a member of Podocarpaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 58–67.