Fine structural observations on the epidermis

Summary In species of Apium, Eryngium and Humulus, the cuticular membrane of the petiole could be resolved into two parts, of which the inner one appeared amorphous and after staining appeared to be penetrated by an electron-dense reticulum, whereas the outer layer showed a lamellate structure consisting of electron-dense and electron-transparent plates, 50–80 Å in thickness. These layers are considered to correspond with the cuticular layer and the cuticle proper, respectively. In species of Abutilon and Rumex the cuticle proper did not exhibit the lamellate structure. In the leaves of Eryngium the outer lamellated structure was present in the cuticle of both young and mature leaves. Both the lamellate and non-lamellate types of the cuticle proper increased in thickness with age of the specimen. The results are discussed in relation to earlier investigations.     

广西百色盆地更新世樟科两种植物角质层研究

本文描述的具角质层的两块叶化石,产自广西百色盆地更新统长蛇岭组。经与现代植物的角质层对比研究后,确定这两块叶化石分属于樟科的两属两种,即油丹(近似种)(Alseoda-phne cf.hainanensis Merr.)和紫楠(近似种)[Phoebe cf.sheareri(Hemsl.)Gamble]。研究结果表明,角质层在鉴定被子植物化石中具有可靠的价值。     

DEVELOPMENT OF THE CUTICULAR LAYERS IN ANGIOSPERM LEAVES

Schieferstein , R. H., and W. E. Loomis . (Iowa State U., Ames.) Development of the cuticular layer in angiosperm leaves. Amer. Jour. Bot. 46(9): 625–635. Illus. 1959.—The cuticularized layers of leaves and other plant surfaces consist of a primary cuticle, formed by the oxidation of oils on exposed cell walls, plus various surface and subsurface wax deposits. The primary cuticle appears to form rapidly on the walls of any living cell which is exposed to air. Surface wax is present on the mature leaves of about half of the 50 or 60 species studied. In general, wax is extruded at random through the newly formed cuticle of young leaves and accumulated in various reticulate to semicrystalline patterns. No wax pores through the cuticle or primary wall can be observed in electron-micrographs of dewaxed mature leaves. Wax accumulations on older leaves are generally subcuticular and may involve the entire epidermal wall. These deposits appear to be of considerably greater ecological significance than those on the surface. Isolated cuticular membranes from Hedera helix increased slightly in permeability to water with age of the leaf, but permeability to 2,4-D decreased 50 times. Evidence based on the patterns of cellulose in primary walls, of surface wax on growing leaves, of the appearance of the cuticle at the margins of growing epidermal cells, of the forms of the cuticle plates digested from growing and older leaves, and of the marginal location of new wax deposits on growing maize leaves is presented to support the thesis that the enlargement of the outer surface of the epidermal cells of leaves occurs at the margins of the surface. Earlier formed cuticle and wax are thus undisturbed during growth. These observations, coupled with evidence for apical growth in fibers, root hairs, etc. suggest that the primary walls of angiosperm cells are formed in specific, localized growth regions, rather than by plastic extension and apposition.     

藏东南色季拉山薄毛海绵杜鹃叶解剖结构特征与环境适应性

以藏东南色季拉山9个不同海拔梯度的薄毛海绵杜鹃(Rhododendron aganniphum var.schizopeplum)叶片为试验材料,采用石蜡切片技术,测定10项叶片解剖结构指标,应用叶片解剖结构指标的可塑性指数和相关性分析方法探索薄毛海绵杜鹃对藏东南色季拉山强紫外辐射和高寒环境的适应性。结果表明:(1)薄毛海绵杜鹃叶片为异面叶,上表皮有明显的角质层,下表皮有表皮毛,栅栏组织细胞2～3层。(2)随着海拔的升高,叶片角质层厚度、上下表皮厚度、栅栏组织厚度、海绵组织厚度、叶片厚度呈现明显增大趋势,而组织结构紧密度和疏松度变化不显著,主脉突起度呈现下降趋势。(3)各项叶片解剖结构指标的可塑性指数显示,薄毛海绵杜鹃在解剖结构上表现出较小的可塑性,对外界环境的适应能力较弱。(4)依据薄毛海绵杜鹃各项叶片解剖结构指标的相关性分析结果,除海绵组织厚度与栅栏组织厚度、下表皮厚度与上角质层厚度之间相关性不显著外,其余各指标之间均呈显著相关关系,且叶片的解剖结构指标方面也存在明显的协同进化现象。研究发现,藏东南色季拉山薄毛海绵杜鹃通过增加叶片角质层厚度、表皮厚度和叶肉厚度等解剖结构指标的方式增强对外界极端环境的适应能力,从而有利于其在恶劣的高山生境下生存繁衍,使该物种成为生态位理论中的广幅种。     

Comparative study of leaf architecture and cuticles of Nelumbo changchangensis from the Eocene of Hainan Island,China, and the two extant species of Nelumbo (Nelumbonaceae)

Fossil leaves of Nelumbo changchangensis, collected from the Eocene of Hainan Island, China, were studied and compared with those of the extant species of Nelumbo, N. nucifera Gaertn. and N. lutea Willd. The fossil leaves have all the specialized features of extant Nelumbo in leaf architecture, except that the organization of the areolae looks much more irregular than that of extant Nelumbo. Comparisons of the cuticle and epicuticular ultrastructure indicate that: (1) N. changchangensis resembles N. nucifera in that anticlinal cell walls of the lower epidermis are straight along the major veins and near leaf bases and are shallowly undulate with U‐ to V‐shaped undulations inside the areolae; (2) N. changchangensis differs from N. lutea in that anticlinal cell walls of the lower epidermis of the latter are deeply undulate with U‐, V‐ to reversed Ω‐shaped undulations inside the areolae; and (3) epicuticular wax crystals are more densely distributed on the leaves of N. changchangensis and N. nucifera than they are in N. lutea. These findings shed significant light on the cuticle differentiation of fossil and extant Nelumbo species. The morphometric comparisons indicate that almost all the synapomorphies of extant Nelumbo were already present by the Eocene, © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 123–137.     

A STUDY OF LEAF COMPRESSIONS OF KNIGHTIOPHYLLUM FROM EOCENE DEPOSITS OF SOUTHEASTERN NORTH AMERICA

A study was made of the gross morphological characters and cuticular features of several fossil leaves of Knightiophyllum wilcoxianum Berry. These fossil leaves were collected from Eocene deposits exposed in three clay pits in western Tennessee. This investigation refutes the relationship of Knightiophyllum wilcoxianum to the modern genus Knightia and the family Proteaceae as suggested by E. W. Berry.     

Isolation and characterization of a cDNA encoding a membrane bound acyl-CoA binding protein from Agave americana L. epidermis.

A cDNA encoding an acyl-CoA binding protein (ACBP) homologue has been cloned from a cDNA library made from mRNA isolated from epidermis of young leaves of Agave americana L. The derived amino acid sequence reveals a protein corresponding to the membrane-associated form of ACBPs only previously described in Arabidopsis and rice. Northern blot analysis showed that the A. americana ACBP gene is mainly expressed in the epidermis of mature zone of the leaves. The epidermis of A. americana leaves have a well developed cuticle with the highest amounts of the cuticular components waxes, cutin and cutan suggesting a potential role of the protein in cuticle formation.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF NORTH AMERICA: STIPULATE LEAVES OF THE RUBIACEAE INCLUDING A PROBABLE POLYPLOID POPULATION

A comparative study was made of the gross morphology, fine venation and cuticular features of Leitneria fioridana Chapman, the single living representative of the order Leitneriales and Leitneria eocenica (Berry) Brown, presumbaly a related fossil species. In addition to the type material, newly collected fossil specimens were investigated from clay pits in the Middle Eocene, Claiborne Formation, of western Tennessee and Kentucky. Foliate stipules attached to the petioles of several specimens suggest the assignment of this fossil leaf type to the genus Leitneria is incorrect. The nature of the gross morphology, fine venation and cuticular features confirms the misidentification. Previously, various specimens of this fossil leaf type have been placed in eight species of seven genera in seven families of six angiosperm orders, none of which are correct systematically. The gross morphology, venation and cuticular characters of the fossil leaf are distributed among a few extant South American genera of arborescent Rubiaceae. The fossil is an extinct rubiaceous leaf type which cannot be placed within a single modern subfamily, tribe or genus of the family. The organ genus, Paleorubiaceophyllum is proposed for these leaves. Three varieties of a single fossil species, P. eocenicum, are recognized. One variety with epidermal cells nearly twice the size of the others may represent a polyploid population.     

Studies on the Ultrastructure and Histochemistry of Plant Cuticles: The Cuticular Membrane of Agave americana L. in situ

The outer epidermal wall of Agave americana leaves was examinedin order to gain more information about the location and chemicalconstitution of the structural components. In middle aged leavesthe wall comprised six layers which were designated epicuticularwax, cuticle proper, exterior and interior cuticular layer,exterior and interior cellin wall. A lamellated structure, consistingof a series of electron translucent lamellae of uniform thicknessalternating with opaque ones of variable thickness, was observedin the thin cuticle proper on the outside of the cuticular membrane,even without heavy metal treatment. The cuticular layers underneathformed the bulk of the cuticular membrane and they also hadtwo components, an amorphous matrix permeated by a reticulumof fibrillae. Cutin, detected with osmium and with iodine/iodine-sulphuricacid–silver proteinate, was a major component of the opaquelamellae of the cuticle proper and the matrix of the cuticularlayer. Carbohydrates were absent from the cuticle proper butwere detected specifically in the fibrillae of the cuticularlayer and in the cellin wall. Pectic material seemed to be presenton both sides of the junction between cuticular membrane andcellin wall, but no discrete zone corresponding to light microscopicalobservations was detected in the electron microscope. Althoughthe lucent lamellae of the cuticle proper were tentatively ascribedto wax there was no structural or ultrahistochemical evidencefor the wax component of the cuticular layer. The various ultrahistochemicalreactions are discussed in relation to the known chemical compositionof the membrane. Agave americana L., epidermis wall, cuticular membrane, cuticle proper, cuticular layer, ultrahistochemistry, wax     

Two Steps of Gas Exchange in Leaf Photosynthesis

Photosynthesis and transpiration of excised leaves of Taraxacum officinale L. and a few other species of plants were measured, using an open gas analysis system. The rates of CO₂ uptake and transpiration increased in two steps upon illumination of stomata-bearing epidermis of these leaves at a light intensity of 50 mW × cm⁻². Abscisic acid inhibited only the second step of gas exchange. Illumination of the astomatous epidermis of hypostomatous leaves caused only the first step of gas exchange. These data indicate that the first and second steps arise from cuticular and stomatal gas exchange, respectively. The rate of the cuticular photosynthesis in a Taraxacum leaf reached saturation at a light intensity of 5 mW × cm⁻², and the rates of the stomatal photosynthesis and transpiration reached saturation at a higher intensity of 35 mW × cm⁻². The cuticular photosynthesis of a Taraxacum leaf was 18% of the stomatal photosynthesis at 50 mW × cm⁻² and 270% at 5 mW × cm⁻². The other species of leaves showed the same trend. The importance of cuticular CO₂ uptake in leaf photosynthesis, especially under low light intensity was stressed from these data.     

Disentangling the assembly mechanisms of ant cuticular bacterial communities of two Amazonian ant species sharing a common arboreal nest

Bacteria living on the cuticle of ants are generally studied for their protective role against pathogens, especially in the clade of fungus‐growing ants. However, little is known regarding the diversity of cuticular bacteria in other ant host species, as well as the mechanisms leading to the composition of these communities. Here, we used 16S rRNA gene amplicon sequencing to study the influence of host species, species interactions and the pool of bacteria from the environment on the assembly of cuticular bacterial communities on two phylogenetically distant Amazonian ant species that frequently nest together inside the roots system of epiphytic plants, Camponotus femoratus and Crematogaster levior. Our results show that (a) the vast majority of the bacterial community on the cuticle is shared with the nest, suggesting that most bacteria on the cuticle are acquired through environmental acquisition, (b) 5.2% and 2.0% of operational taxonomic units (OTUs) are respectively specific to Ca. femoratus and Cr. levior, probably representing their respective core cuticular bacterial community, and (c) 3.6% of OTUs are shared between the two ant species. Additionally, mass spectrometry metabolomics analysis of metabolites on the cuticle of ants, which excludes the detection of cuticular hydrocarbons produced by the host, were conducted to evaluate correlations among bacterial OTUs and m/z ion mass. Although some positive and negative correlations are found, the cuticular chemical composition was weakly species‐specific, suggesting that cuticular bacterial communities are prominently environmentally acquired. Overall, our results suggest the environment is the dominant source of bacteria found on the cuticle of ants.     

Determination of diffusion coefficients of octadecanoic acid in isolated cuticular waxes and their relationship to cuticular water permeabilities

Transport properties of cuticular waxes from 40 different plant species were investigated by measuring desorption rates of ¹⁴C-labelled octadecanoic acid from isolated and subsequently reconstituted wax. Diffusion coefficients (D) of octadecanoic acid in reconstituted waxes, calculated from the slopes of the regression lines fitted to the linearized portions of desorption kinetics, ranged from 1.2 × 10^?19 m² s^?1 (Senecio kleinia leaf) to 2.9 × 10^?17 m² s^?1 (Malus cf. domestica fruit). Cuticular water permeabilities (cuticular transpiration) measured with intact cuticular membranes isolated from 24 different species varied from 1.7 × 10^?11 m s^?1 (Vanilla planifolia leaf) up to 2.1 × 10^?9 m s^?1 (Malus cf. domestica fruit), thus covering a range of more than 2 orders of magnitude. Cuticular water permeabilities were highly correlated with diffusion coefficients of octadecanoic acid in isolated cuticular wax of the same species. It is therefore possible to estimate cuticular barrier properties of stomatous leaf surfaces or of leaves where isolation of the cuticle is impossible by measuring D of octadecanoic acid in isolated waxes of these leaves.     

Temporal programming of epidermal cell protein synthesis during the larval-pupal transformation ofManduca sexta

Summary During the final larval instar the epidermis of the tobacco hornworm,Manduca sexta, synthesizes the larval cuticular proteins and the pigment insecticyanin. Then at the onset of metamorphosis the cells first become pupally-committed, then later produce the pupal cuticle. The changes in the pattern of epidermal protein synthesis during this period were followed by incubating the integument in vitro with either³H-leucine or³⁵S-methionine, then analyzing the proteins by 2-dimensional gel electrophoresis. Precipitation by larval and pupal cuticular antisera and by insecticyanin antibody identified these proteins. Three distinct changes in epidermal protein synthesis were noted: 1) Stage-specific proteins, some of which are larval cuticular proteins, appear just before and during the change of commitment on day 3. (2) By late the following day (wandering stage), synthesis of these and many other proteins including all the identified larval cuticular proteins and insecticyanin was undetectable. Several noncuticular proteins were transiently synthesized by this pupally committed cell during wandering and sometimes the following day. (3) During the production of pupal cuticle a new set of pupal-specific cuticular proteins as well as some common cuticular proteins (precipitated by both antisera) were synthesized. Some of the latter were also synthesized during the period between pupal commitment and pupal cuticle deposition.In spite of an apparent absence of methionine in both larval and pupal cuticle, many cuticular proteins incorporated³⁵S-methionine. Thus they may be synthesized as proproteins.Insecticyanin was shown to have two forms differing in isoelectric point, the cellular form being more acidic than the hemolymph form. Synthesis of the cellular form ceased before that of the hemolymph form.     

Cuticular Studies on Two Pleistocene Species of Lauraceae in Baise Basin,Guangxi

Two fossil leaves with cuticle described here were collected from the Pleistocene Changseling Formation of Baise Basin, Guangxi. A detailed comparison of the cuticular analysis between the fossils and their living equivalents indicated that the two fossil species belong to 2 genera of Lauraceae, that is, Alseodaphne of, hainanensis Merr. and Pheobe cf. sheareri (Hemsl.) Gamble. The first report on lauraceous fossil leaves with cuticle in China showed that cuticular analysis had a reliable value in identifying the angiospermous fossil plants.     

STRUCTURE OF THE PEAR LEAF CUTICLE WITH SPECIAL REFERENCE TO CUTICULAR PENETRATION

Study of the pear leaf cuticle (Pyrus communis L. ‘Bartlett‘), in both intact and enzymatically isolated forms, has revealed that the cuticular membrane is separated from the underlying epidermal cell wall by a layer of pectic substances which extend into but not through the membrane. A layer of embedded birefringent waxes occurs towards the outer surface of the cuticular membrane. Platelet-like epicuticular waxes are deposited on the outer surface. The upper cuticular membrane is astomatous. The lower epidermis is stomatous, and the outer cuticular membrane is continuous with that lining the substomatal cavity. The lower cuticular membrane is also generally thicker than the upper, and both the upper and lower cuticular membranes are thicker over veinal than over mesophyll tissue. The birefringence frequently is discontinuous over anticlinal walls and over veinal tissue. The lower cuticle appears to contain fewer embedded waxes (as indexed by birefringence) than the upper. Enzymatic isolation of the cuticular membrane from the underlying tissues does not appear to cause any discernible change in structure as viewed with a light microscope. These findings are discussed in light of current knowledge concerning penetration of foliar applied substances into the leaf.     

Development of plant cuticles: fine structure and cutin composition of Clivia miniata Reg. leaves

The fine structure and monomeric composition of the ester-cutin fraction (susceptible to BF₃/CH₃OH transesterification) of the adaxial leaf cuticle of Clivia miniata Reg. were studied in relation to leaf and cuticle development. Clivia leaves grow at their base such that cuticle and tissues increase in age from the base to the tip. The zone of maximum growth (cell expansion) was located between 1 and 4 cm from the base. During cell expansion, the projected surface area of the upper epidermal cells increased by a factor of nine. In the growth region the cuticle consists mainly of a polylamellate cuticle proper of 100–250 nm thickness. After cell expansion has ceased both the outer epidermal wall and the cuticle increase in thickness. Thickening of the cuticle is accomplished by interposition of a cuticular layer between the cuticle proper and the cell wall. The cuticular layer exhibits a reticulate fine structure and contributes most of the total mass of the cuticle at positions above 6 cm from the leaf base. The composition of ester cutin changed with the age of cuticles. In depolymerisates from young cuticles, 26 different monomers could be detected whereas in older ones their number decreased to 13. At all developmental stages, 9,16-/10,16-dihydroxyhexadecanoic acid (positional isomers not separated), 18-hydroxy-9-octadecenoic acid, 9,10,18-trihydroxyoctadecanoic acid and 9,10-epoxy-18-hydroxyoctadecanoic acid were most frequent with the epoxy alkanoic acid clearly predominating (47% at 16 cm). The results are discussed as to (i) the age dependence of cutin composition, (ii) the relationship between fine structure and composition, (iii) the composition of the cuticle proper, the cuticular layer and the non-depolymerizable cutin fraction, and (iv) the polymeric structure of cutin.Abbreviations CL cuticular layer - CP cuticle proper - MX cutin polymer matrix     

A fine structural analysis of the epidermis and cuticle of the oligochaete aeolosoma Bengalense stephenson

The fine structure of the epidermis and cuticle has been described for the oligochaete Aeolosoma bengalense. The epidermis is a pseudostratified epithelium and consists of the following cell types: ciliated and nonciliated supportive cells, pigment cells and associated satellite cells, mucous cells, basal cells, and ciliated non-supportive columnar cells. Overlying and restricted to the supportive cells is a delicate cuticle composed of: (a) a discontinuous layer of membrane-bounded surface particles; (b) a thin filamentous layer of moderate electron density just under the surface particles; (c) a thicker inner filamentous layer of low electron density. Digestion with pronase effectively removes the cuticle. This, together with the fact that it stains with alcian blue and ruthenium red, indicates that the cuticle contains an acid mucopolysaccharide. Regeneration of the cuticle, following pronase treatment, is marked by the elaboration of numerous microvilli by the supportive cells. Most of the microvilli are transitory and evidence supports a microvillar origin for the cuticular surface particles. The presence of cuticular surface particles may be a characteristic shared in common by all oligochaetes and, perhaps, some polychaetes.