Do leaves in Cyperoideae (Cyperaceae) have a multiple epidermis or a hypodermis?

In Cyperaceae, leaf anatomical characters, in particular the presence of a hypodermis or of a multiple epidermis, have contributed in taxonomic and phylogenetic studies. In this family, the leaf epidermis is often described as uniseriate, and the cells of the subepidermal layers having no chloroplasts are treated as hypodermis. Both tissues have a different ontogenetic origin and hence are not homologous. The aim of the present work was to verify the origin of the subepidermal layers in eight species belonging to Cyperoideae. All species studied presented multiple epidermal layers that were confirmed by leaf ontogeny. In Fimbristylis complanata, F. dichotoma, Pycreus flavescens and P. polystachyos the mature leaves present multiple epidermal layers with cells of the distinct layers similar in shape and size; in the other species studied these cells are different. Especially in the latter case, a multiple epidermis is easily interpreted erroneously as a hypodermis, possibly leading to erroneous evolutionary conclusions. Making correctly distinction between a hypodermis and a multiple epidermis, and hence in case of doubt investigating the origin of the questioned tissue, is compulsory in order to use both characters in a phylogenetic context. Though in the past often called ‘hypodermis’, our leaf ontogenetical observations show that in all species studied, the subepidermical layers constitute a multiple epidermis, originating from the protodermis.     

A quantitative analysis of the interspecific plasmodesmata in the non-division walls of the plant chimera Laburnocytisus adamii (Poit.) Schneid.

Non-division walls in petals of the chimera Laburnocytisus adamii (Poit.) Schneid, were screened for the occurrence and distribution of symplasmic connections. The secondary plasmodesmata (PD) between epidermal cells of Cytisus purpureus Scop, and subepidermal cells of Laburnum anagyroides Medik. were compared with the PD of corresponding cell walls in petals of the two parental species. The non-division walls in the petals of L. adamii were traversed mainly by continuous PD and a few half-PD, both being grouped in pit fields. The secondary PD were characterized by a high percentage of branching (82%), with more than 40% consisting of a single strand at the Cytisus cell side interconnected by a median cavity with two strands of the Laburnum subepidermal cell. In addition, more than 30% of all PD showed secondary branching in the subepidermal wall portion. As a consequence, the cross-sectional areas of plasmodesmatal strands on each side of the central cavity differed remarkably in size, representing a “bottleneck” in the epidermal wall portion. In contrast, PD in the petals of the parental species were symmetrically branched. The comparison of cross-sectional areas of PD in the cell wall between the epidermis and subepidermis of petals of L. anagyroides showed a well-tuned system. The occurrence of half-PD in the intraspecific wall indicates a secondary origin. We conclude that, in the chimera, both genotypically different cells take part in the formation of the interspecific PD.     

Induction of adventitious buds in cultured petal explants ofChelidonium majus L.

Petal explants ofChelidonium majus L. (Papaveraceae) formed noteworthy adventitious buds without any intermediate callus when cultured under appropriate conditions. Bud formation was favored by combinations of 1–2 mg/l indoleacetic acid (IAA) and/or 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.1–0.5 mg/l kinetin (K). In the present study, neither bud formation nor callus formation occurred in cultures of excised leaves. A histological study revealed that adventitious bud formation occurred only in single epidermal layers of petals, while several subepidermal parenchyma layers did not join in its formation. Activation zones arising from the epidermis underwent intense cell divisions to initiate buds on the epidermal surface. These buds later turned green in color, developing into shoots which eventually grew into plantlets after root formation.     

枫香变红过程中叶片组织结构、光合特性及色素含量变化研究

枫香(Liquidambar formosana)因其叶片入秋后逐渐变红而极具观赏价值,是优良的景观生态树种。为了解枫香叶片结构变化与叶色的关系,该文通过连续监测枫香叶片变红过程中组织结构、光合特性及色素含量的变化,分析叶片结构与其光合特性和色素的关系。结果表明：(1)叶片变色过程中,表皮细胞均为椭圆形,紧密排列,未观察到明显的细胞变异,表面未附着绒毛和蜡质,且上表皮细胞与栅栏组织细胞间排列紧密,未出现较大的气室。(2)随着叶片逐渐变红,叶片结构变化显著,其中叶片、上表皮、栅栏组织和海绵组织厚度及气孔开度均逐渐减小,而气孔器长和宽、单个气孔器面积则逐渐增大。(3)随着叶片结构的变化,其叶绿素含量逐渐减少,致使净光合速率逐渐减小,在出现光破坏时,叶片通过在栅栏组织细胞液泡内合成花色苷来自我保护,而大量的花色苷致使叶片表面呈现红色。综上认为,叶绿素含量降低,花色素苷大量积累是导致枫香叶片变红的直接原因,而枫香叶色变红则是其一系列生理结构特征综合作用的结果。     

Histological events leading to somatic embryo formation in cultured petioles of alfalfa

Summary An optimum 10-day exposure of petioles of alfalfa [Medicago sativa ssp.falcata (L.) Arcangeli] to 2,4-dichlorophenoxyacetic acid or 2,4,5-trichlorophenoxyacetic acid results in the semisynchronous production of somatic embryos starting about 4 days after transfer to a non-auxin-containing medium. The timing of cell division induction in the petiole explants was found to vary depending on the petiole tissue type. Cells adjacent to the vascular bundles divide first at about 48 h after exposure to auxin, closely followed by those of the inner parenchyma, whereas most of the cells of the subepidermal and epidermal layers start to divide later, between 72 and 120 h. Two different sources of callus were also evident. Cells adjacent to the vascular bundles and the inner parenchyma cells were the primary source of callus when a short, 2-day (non-embryo-producing) exposure to auxin was used. In contrast, the subepidermal and epidermal cells were the primary source of callus tissue when a longer, 10-day (embryo producing) exposure was used. It is concluded that the source of somatic embryos is primarily the daughter cells of the subepidermal or epidermal tissue or both.     

Polygalacturonase45 cleaves pectin and links cell proliferation and morphogenesis to leaf curvature in Arabidopsis thaliana

Regulating plant architecture is a major goal in current breeding programs. Previous studies have increased our understanding of the genetic regulation of plant architecture, but it is also essential to understand how organ morphology is controlled at the cellular level. In the cell wall, pectin modification and degradation are required for organ morphogenesis, and these processes involve a series of pectin-modifying enzymes. Polygalacturonases (PGs) are a major group of pectin-hydrolyzing enzymes that cleave pectin backbones and release oligogalacturonides (OGs). PG genes function in cell expansion and separation, and contribute to organ expansion, separation and dehiscence in plants. However, whether and how they influence other cellular processes and organ morphogenesis are poorly understood. Here, we characterized the functions of Arabidopsis PG45 (PG45) in organ morphogenesis using genetic, developmental, cell biological and biochemical analyses. A heterologously expressed portion of PG45 cleaves pectic homogalacturonan in vitro, indicating that PG45 is a bona fide PG. PG45 functions in leaf and flower structure, branch formation and organ growth. Undulation in pg45 knockout and PG45 overexpression leaves is accompanied by impaired adaxial–abaxial polarity, and loss of PG45 shortens the duration of cell proliferation in the adaxial epidermis of developing leaves. Abnormal leaf curvature is coupled with altered pectin metabolism and autogenous OG profiles in pg45 knockout and PG45 overexpression leaves. Together, these results highlight a previously underappreciated function for PGs in determining tissue polarity and regulating cell proliferation, and imply the existence of OG-based signaling pathways that modulate plant development.     

Solute sorting in grass leaves: the transpiration stream

Solutes distribute differentially between leaf tissues and cells. The present study tested the hypothesis that certain solutes are supplied preferentially to the epidermis in the transpiration stream, by-passing mesophyll cells along bundle sheath extensions. Using energy dispersive X-ray analysis of extracted cell sap, the distribution of solutes was studied in the emerged zone (transpiring) and the elongation zone (non-transpiring) of the developing leaf three of barley (Hordeum vulgare L.). The basic distribution of Cl, K, P and Ca between epidermis and bulk tissue, and between cells within the epidermis, was similar in the two leaf regions. However, in the emerged zone differences in solute concentrations between tissues and cells were greater. A local reduction in transpiration rate along the emerged portion of the blade specifically prevented Ca from accumulating to high levels in epidermal cells close to stomata. It is concluded that differences in solute concentrations between epidermal cells and other leaf tissues can be established in the absence of transpiration, but that they require transpiration for their full expression. Peristomatal transpiration appears to be responsible for high Ca in interstomatal cells.Abbreviations EDX-analysis Energy-dispersive X-ray analysis - IS-cell Interstomatal cell - R-cell Ridge cell - TR-cell Trough cell     

Epidermal jasmonate perception is sufficient for all aspects of jasmonate‐mediated male fertility in Arabidopsis

Jasmonate (JA) signaling is essential for several environmental responses and reproductive development in many plant species. In Arabidopsis thaliana, the most obvious phenotype of JA biosynthetic and perception mutants is profound sporophytic male sterility characterized by failure of stamen filament elongation, severe delay of anther dehiscence and pollen inviability. The site of action of JA in the context of reproductive development has been discussed, but the ideas have not been tested experimentally. To this end we used targeted expression of a COI1‐YFP transgene in the coi1‐1 mutant background. As COI1 is an essential component of the JA co‐receptor complex, the null coi1‐1 mutant is male sterile due to lack of JA perception. We show that expression of COI1‐YFP in the epidermis of the stamen filament and anther in coi1 mutant plants is sufficient to rescue filament elongation, anther dehiscence and pollen viability. In contrast, filament expression alone or expression in the tapetum do not restore dehiscence and pollen viability. These results demonstrate that epidermal JA perception is sufficient for anther function and pollen viability, and suggest the presence of a JA‐dependent non‐autonomous signal produced in the anther epidermis to synchronize both anther dehiscence and pollen maturation.     

黄瓜花原基的形成及与Ca~(2+)的关系

以黄瓜为试验材料研究了肉眼可见的花原基突起之前 ,花原基早期的分化过程。结果显示花原基分化和开花的起始节位是第一真叶节 ;肉眼可见花原基突起前早期的分化是在叶腋亚表皮部位形成一个球形的花原基起始细胞团 ,此细胞团进一步分裂、扩大形成肉眼可见的花原基突起 ;第一真叶节的花原基起始细胞团分化集中发生于 6～ 7d苗龄时期 ;Ca2 + 在花原基起始细胞团细胞中主要分布在细胞壁和细胞间隙 ,而在非起始细胞团的叶腋亚表皮细胞则主要分布在液泡中 ,并对Ca2 + 在花原基起始细胞团分化中的作用进行了讨论。     

Secondary phenolic products in isolated guard cell,epidermal cell and mesophyll cell protoplasts from pea (Pisum sativum L.) leaves: Distribution and determination

Summary Guard cells and epidermal cells of the abaxial (lower) and adaxial (upper) epidermis ofPisum sativum L., mutant Argenteum, are the predominant sites of flavonoid accumulation within the leaf. This was demonstrated by the use of a new method of simultaneous isolation and separation of intact, highly-purified guard cell and epidermal cell protoplasts from both epidermal layers and of protoplasts from the mesophyll. Isolated guard and epidermal protoplasts retained flavonoid patterns of the parent epidermal tissue; quercetin 3-triglucoside and its p-coumaric acid ester as major constituents, kaempferol 3-triglucoside and its p-coumaric acid ester as minor compounds. Total flavonoid content in the lower epidermis was estimated to be ca. 80 fmol per guard cell protoplast and 500 fmol per epidermal cell protoplast. Protoplasts isolated from the upper epidermis had about 20–30% as much of these flavonoids. Mesophyll protoplasts retained only about 25 fmol total flavonoid per protoplast.By fluorescence microscopy, using the alkaline-induced yellow-green fluorescence characteristics of flavonols, we suggest that these flavonol glycosides are present in cell vacuoles. There was no indication for the presence of flavine-like compounds.Abbreviations uE adaxial (upper) epidermis - IE abaxial (lower) epidermis - GCP guard cell protoplasts - ECP epidermal cell protoplasts - MCP mesophyll cell protoplasts - PP protoplasts - HPLC high performance liquid chromatography - TLC thin layer chromatography - CC column chromatography - HOAc acetic acid     

In vitro studies on the anatomy and morphology of bud regeneration in melon cotyledons

Summary The anatomy and morphology of bud regeneration were investigated in melon (Cucumis melo L.) cv. Galia, which regenerates in vitro only by direct organogenesis from the cotyledon explant. Explants were cut from the cotyledon proximal to the apex from 3-d-old in vitro seedlings. After 3 d on Murashige and Skoog medium with N⁶-benzyladenine, cell division can be observed in the epidermal layer on the adaxial side in the center of the explant, near the most proximal (wounded) cut edge. Over the next week, the area of the meristem increases laterally. Additional cell layers are added to the meristematic area by cell division in the epidermis. In places the epidermis remains active in cell division. Alongside those active areas there are zones where the epidermis has become inactive, although the subepidermal layers continue to divide. In transverse section, the explant now has small protuberances on the adaxial surface. After 10 d on cytokinin-containing medium, the first signs of development are visible on the adaxial surface adjacent to the proximal cut edge. The protuberances observed after 10 d are neither primordia nor buds, although some meristematic bulges are observed. The first regenerated shoot buds are observed histologically after 15 d, by which time the surface has many protuberances and some small leaves. The first shoot is found by histology after 22 d. By this time the surface is covered with protrusions and leaves, mostly without accompanying buds. The leaves may be produced from the protrusions initially visible after 10 d.     

Salinity Stiffens the Epidermal Cell Walls of Salt-Stressed Maize Leaves: Is the Epidermis Growth-Restricting?

As a result of salt (NaCl)-stress, sensitive varieties of maize (Zea mays L.) respond with a strong inhibition of organ growth. The reduction of leaf elongation investigated here has several causes, including a modification of the mechanical properties of the cell wall. Among the various tissues that form the leaf, the epidermis plays a special role in controlling organ growth, because it is thought to form a rigid outer leaf coat that can restrict elongation by interacting with the inner cell layers. This study was designed to determine whether growth-related changes in the leaf epidermis and its cell wall correspond to the overall reduction in cell expansion of maize leaves during an osmotic stress-phase induced by salt treatment. Two different maize varieties contrasting in their degree of salt resistance (i.e., the hybrids Lector vs. SR03) were compared in order to identify physiological features contributing to resistance towards salinity. Wall loosening-related parameters, such as the capacity of the epidermal cell wall to expand, β-expansin abundance and apoplastic pH values, were analysed. Our data demonstrate that, in the salt-tolerant maize hybrid which maintained leaf growth under salinity, the epidermal cell wall was more extensible under salt stress. This was associated with a shift of the epidermal apoplastic pH into a range more favourable for acid growth. The more sensitive hybrid that displayed a pronounced leaf growth-reduction was shown to have stiffer epidermal cell walls under stress. This may be attributable to the reduced abundance of cell wall-loosening β-expansin proteins following a high salinity-treatment in the nutrient solution (100 mM NaCl, 8 days). This study clearly documents that salt stress impairs epidermal wall-loosening in growth-reduced maize leaves.     

Fused organs in the adherent1 mutation in maize show altered epidermal walls with no perturbations in tissue identities

In the absence of wounding, the epidermis is only rarely involved in cell or organ fusion events; in fact, intact epidermal layers prevent graft unions. In Zea mays L. the mutation adherent1 (ad1) shows abnormal fusions between cells and organs. Fusions involve epidermal cells of vegetative and floral organs and occur early in the ontogeny of organs. Even so, epidermal cell types differentiate normally in the fused regions and internal tissue identities are maintained. In contrast, the extracellular matrix (cell wall and cuticle) of the epidermal cells is perturbed. Epidermal cell walls in adherent leaves are thicker than normal. Epicuticular wax particles appear reduced in size and number and altered in shape in mutant leaves. In addition, the outer epidermal cell walls of adherent leaves fluoresce when stained with aniline blue, a reagent that binds to callose. Immunolocalizations to specific cell wall epitopes suggest that pectins but not arabinogalactans may have a role in the fusion events. Taken together, these results suggest that the ad1 mutation results in cell-wall and epicuticular-wax defects similar to responses seen in wounding, pollination by incompatible pollen, or pathogen attack. Since cell wall components and epicuticular waxes are extracellular secreted products, the ad1 mutation may disrupt normal functioning and/or composition of the secretory pathway and its cargo. Received: 30 January 1998 / Accepted: 5 March 1998     

Structure and Function in the Grass Ligule: Optical and Electron Microscopy of the Membranous Ligule of Lolium temulentum L.

Aspects of the structure and ultrastructure of the membranousligule of mature leaves of Lolium temulentum L. are described.In transverse section the ligule was lens-shaped and wedge-shapedin longitudinal section, 6 or 7 cells wide near the base and1 or 2 cells wide at the edges. Two uniseriate epidermes encloseda chlorenchymatous mesophyll tissue of varying thicknesses;both epidermes were continuous with the leaf adaxial epidermis.The cells comprising these three issues all appeared like typicalgrass epidermal long cells; elongate papillate cells were presentat the edges. No stomata, trichomes, intercellular spaces orvascular tissue were found in the ligule. A marked polarizationof ultrastructural complexity existed from the large-vacuolateabaxial epidermis to the ‘densely cytoplasmic’ small-vacuolateadaxial epidermis. Cells of the latter tissue contained numerousmitochondria, hypersecretory dictyosomes and abundant strandsof rough endoplasmic reticulum. Fluorescence microscopy providedevidence for the accumulation of a polysaccharide-containingmaterial within the periplasmic space next to the outer tangentialwall of adaxial epidermal cells. The ligule is considered tobe a highly organized and differentiated leaf organ with a pholosyntheticmesophyll and an adaxial epidermis active in the synthesis ofprotein and polysaccharide. Darnel, fluorescence microscopy, ligule, Lolium temulentum L., Poaceae, ultrastructure     

Cell-lineage patterns in the shoot apical meristem of the germinating maize embryo

A fate map for the shoot apical meristem of Zea mays L. at the time of germination was constructed by examining somatic sectors (clones) induced by -rays. The shoot apical meristem produced stem, leaves, and reproductive structures above leaf 6 after germination and the analysis here concerns their formation. On 160 adult plants which had produced 17 or 18 leaves, 277 anthocyanin-deficient sectors were scored for size and position. Sectors found on the ear shoot or in the tassel most often extended into the vegetative part of the plant. Sectors ranged from one to six internodes in length and some sectors of more than one internode were observed at all positions on the plant. Single-internode sectors predominated in the basal internodes (7,8,9) while longer sectors were common in the middle and upper internodes. The apparent number of cells which gave rise to a particular internode was variable and sectors were not restricted to the lineage unit: a leaf, the internode below it, and the axillary bud and prophyll at the base of the internode. These observations established two major features of meristem activity: 1) at the time of germination the developmental fate of any cell or group of cells was not fixed, and 2) at the time of germination cells at the same location in a meristem could produce greatly different amounts of tissue in the adult plant. Consequently, the developmental fate of specific cells in the germinating meristem could only be assigned in a general way.Abbreviations ACN apparent cell number - LI, LII, LI-LII sectors restricted to the epidermis, the subepidermis, or encompassing epidermis and subepidermis - PCN progenitor cell     

Two new grape cultivars, bud sports of Cabernet Sauvignon bearing pale-coloured berries, are the result of deletion of two regulatory genes of the berry colour locus

Bud sports are infrequent changes in phenotype affecting shoots of woody perennials but the molecular basis of these mutations has rarely been identified. In this report, we show that the bronze-coloured berries of the Malian cultivar, a documented bud sport of the wine grape Cabernet Sauvignon (Vitis vinifera L.), lack anthocyanins in the subepidermal cells compared to the red/black berried Cabernet Sauvignon in which both the epidermis and several subepidermal cell layers contain anthocyanin. The Malian phenotype is correlated with an alteration in the genome indicated by a reduction of hybridisation signal using a MYBA probe. In Shalistin, a white-berried bud sport of Malian, the red allele at the berry colour locus appears to have been deleted completely. These data suggest that Malian could be a L1/L2 periclinal chimera, which gave rise to Shalistin by an invasion of epidermal cells (L1) by the mutated subepidermal cells (L2). The red grape Pinot Noir has given rise to a number of pale coloured sports, although the provenance of the extant sports is not known. We show that a clone of Pinot Blanc (white-berried) does not have a deletion of the red allele of the same dimensions as that in Shalistin, though a small deletion is a likely explanation for the altered phenotype. However, the mechanism of deletion of the red allele of the berry colour locus is a possible means by which other red to white clonal mutations of grapevines have occurred.