Lognormal distribution of water permeability and organic solute mobility in plant cuticles

It is shown that water permeabilities and organic solute mobilities in plant cuticles have a lognormal distribution. Seven-hundred and fifty values for rate constants of desorption (～mobility) of 2,4-D from isolated Citrus aurantium L. cuticles from a population of leaves were pooled and analysed. A histogram of the rate constants of individual cuticles showed a skew distribution with a strong tail to higher values. Cuticular membranes with high values did not differ from others in visual appearance and were not leaky. After log-transformation of original data an almost perfect normal distribution was obtained. Statistical tests showed that a normal distribution of original values is not acceptable. Inspection of older data for water permeability in the same species and experiments using large samples of cuticles from leaves of Pyrus communis L. and Stephanotis floribunda Brongn. and from fruits of Capsicum annuum L. showed a similar distribution, as did inspection of data for experiments with organic solutes. A lognormal distribution was found for cuticles of plants from growth chambers, glasshouses and outdoors as well as for water permeability of intact leaves of Hedera helix L. For small samples the overestimation from using the arithmetic mean of original data can be high, but use of the geometric mean or the median leads to smaller deviations. Removing cuticular waxes from cuticles produced normally distributed samples. A normal distribution was also obtained when organic compounds which increase solute mobility were sorbed into cuticles.     

Trilobite cuticle thickness in relation to palaeoenvironment

100 thickness measurements from thin sections of cephala or pygidia of early Ordovician trilobites occurring across an onshore to offshore environmental gradient show that progressively greater maximum cuticle thickness was characteristic of increasingly inshore sites. There is a 40-fold difference between the thinnest and thickest cuticles, and exclusively thin cuticles are confined to the offshore Olenid Biofacies. Variability in cuticle thickness increases offshore to onshore. Environmental control is shown to be more influential on cuticle thickness than is the overall length of the trilobite: some comparatively large trilobites having thin cuticles and small trilobites thick cuticles. The environmental factors which might be responsible for the pattern are briefly discussed. The thin cuticles dominating the offshore Olenid Biofacies were probably appropriate for dysaerobic conditions. Thick cuticles in the most inshore biofacies may have offered protection against predators and turbulence, but the additional presence there of trilobites with thinner cuticles is considered to reflect the greater heterogeneity of the epeiric habitat.     

Vital staining of glycoprotein secreted by infective third stage larvae of Haemonchus contortus prior to exsheathment.

Staining of infective third stage larvae of Haemonchus contortus prior to exsheathment shows that protein is exuded from the head region and spreads between the cuticles and that a carbohydrate-containing substance is also found between the L2 and L3 cuticles throughout, at exactly the same sites in this nematode. This glycoprotein, which is either secreted from the mouth or the amphids or both is exuded whether or not the larvae have been stimulated to exsheath. Slight staining was also sometimes detected at the secretory-excretory pore and to an even lesser extent at the anus. This glycoprotein is thought to function as a lubricant to prevent abrasion between the cuticles. It accumulates in areas where there is greatest space between the cuticles such as the head, tail and where bending of the nematode body occurs.     

中国华夏植物区二叠纪几种科达植物分散角质层及其意义

中国华夏植物区科达植物的研究历史虽然最早可上溯至1883年,但直到1991年才首次报道其角质层构造。到目前为止,中国华夏植物区总共描述了4种科达植物原位角质层和3种分散角质层。但与欧美植物区相比,有关中国华夏植物区科达植物角质层的研究工作还较薄弱。本文较详细地描述了3种产自中国华夏植物区二叠纪煤系地层中的科达植物分散角质层。其中2种采自华北亚区南缘的安徽淮南新庄孜矿山西组A1煤顶板,地质时代为早二叠世;另一种采自华南亚区的贵州水城矿区大河边矿龙潭组顶部的11号煤层,地质时代为晚二叠世早期。将这3种科达植物分散角质层与已知的欧美植物区和中国华夏植物区的种类进行了对比,认为它们都是新的类型。讨论了这3种新的科达植物分散角质层所具有的古植物学意义。     

Dispersed cuticles from the Eocene of North America

KOVACH, W. L. & DILCHER, D. L., 1984. Dispersed cuticles from the Eocene of North America. Macerations of organic-rich clay from the Claiborne Formation (Middle Eocene) of Tennessee have yielded a wide variety of well-preserved dispersed cuticles. Details of the epidermal cell patterns, arrangement of the stomata1 complex, trichomes and trichome attachment have made possible the association of some dispersed cuticles with leaf types known from this formation which have similar cuticle, and with modern families. All dispersed cuticles are classified in a morphologic system. Through both our own work and a review of previous investigations we have found that distinct dispersed cuticle types can be recognized and may be used biostratigraphically to characterize geologic strata, palaeo-ecologically to provide insights into environmental reconstruction, and systematically to follow the history of certain taxa.     

Patterns of Effective Permeability of Leaf Cuticles to Acids

Plants in the field are frequently exposed to anthropogenic acid precipitation with pH values of 4 and below. For the acid to directly affect leaf tissues, it must pass through the leaf cuticle, but little is known about the permeability of cuticles to protons, or about the effect of different anions on this permeability. We investigated the movement of protons through isolated astomatous leaf cuticles of grapefruit (Citrus X paradisi Macfady.), rough lemon (Citrus limon [L.] Burm. fils cv Ponderosa), and pear (Pyrus communis L.) using hydrochloric, sulfuric, and nitric acids. Cuticles were enzymically isolated from leaves and placed in a diffusion apparatus with pH 4 acid on the morphological outer surface of the cuticle and degassed distilled water on the inner surface. Changes in pH of the solution on the inner surface were used to determine rates of effective permeability of the cuticles to the protons of these acids. Most cuticles exhibited an initial low permeability, lasting hours to days, then after a short transition displayed a significantly higher permeability, which persisted until equilibrium was approached. The change in effective permeability appears to be reversible. Effective permeabilities were higher for sulfuric acid than for the others. A model of the movement of protons through the cuticle is presented, proposing that dissociated acid groups in channels within the cutin are first protonated by the acid, accounting for the low initial effective permeability; then protons pass freely through the channels, resulting in a higher effective permeability.     

The cuticle of Caenorhabditis elegans. II. Stage-specific changes in ultrastructure and protein composition during postembryonic development

The cuticle of the free-living nematode Caenorhabditis elegans is a proteinaceous extracellular structure that is replaced at each of four postembryonic molts by the underlying hypodermis. The cuticles of the adult and three juvenile stages (L1, Dauer larva, L4) have been compared ultrastructurally and biochemically. Each cuticle has an annulated surface and comprises two main layers, an inner basal layer and an outer cortical layer. The adult cuticle has an additional clear layer which separates the basal and cortical layers and is traversed by regularly arranged columns of electron-dense material. The fine structure of the cortical layer is similar in cuticles from different stages while that of the basal layer is stage specific. Purified cuticles were obtained by sonication and treatment with sodium dodecyl sulfate (SDS) and their component proteins solubilized with a sulfhydryl reducing agent. The degree of cuticle solubility is stage specific and the insoluble structures for each cuticle were localized by electron microscopy. Analysis of ³⁵S-labeled soluble cuticle proteins by SDS-polyacrylamide gel electrophoresis yields unique banding patterns for each stage. Most proteins are of high molecular weight (100–200 K) and are restricted to particular stages. Sixteen of the nineteen major proteins characterized are specifically degraded by bacterial collagenase. The results indicate that the different molts are not reiterative, but require the integration of both unique and shared gene functions. The potential use of stage-specific cuticle differences to identify and characterize regulatory genes controlling cuticle-type switching during development is discussed.     

中国华夏植物区二叠纪几种科达植物分散角质层及其意义

中国华夏植物区科达植物的研究历史虽然最早可上溯至1883年,但直到1991年才首次报道其角质层构造.到目前为止,中国华夏植物区总共描述了4种科达植物原位角质层和3种分散角质层.但与欧美植物区相比,有关中国华夏植物区科达植物角质层的研究工作还较薄弱.本文较详细地描述了3种产自中国华夏植物区二叠纪煤系地层中的科达植物分散角质层.其中2种采自华北亚区南缘的安徽淮南新庄孜矿山西组A1煤顶板,地质时代为早二叠世;另一种采自华南亚区的贵州水城矿区大河边矿龙潭组顶部的11号煤层,地质时代为晚二叠世早期.将这3种科达植物分散角质层与已知的欧美植物区和中国华夏植物区的种类进行了对比,认为它们都是新的类型.讨论了这3种新的科达植物分散角质层所具有的古植物学意义.     

Comparative study of some expanding arthropod cuticles: The relation between composition,structure and function

The abdominal cuticles of the adult female ticks Argas (Persicargas) robertsi and Boophilus microplus, sp der Badumna insignis, tsetse fly Glossina morsitans morsitans, sheep ked Melophagus ovinus and locust Locusta migratoria migratorioides and of the fifth-instar larva of the bug Rhodnius prolixus stretch greatly, some of them quite rapidly, when they are feeding, laying eggs or carrying a developing larva or egg mass. During this expansion the epicuticle, which is convoluted, unfolds and the underlying endocuticle stretches. There is an increase in the volume of each of the cuticles on expansion. The fine structures of those cuticles which go through cycles of expansion and contraction do not become disrupted. Cuticles with acidic proteins have much higher chitin contents than those with basic proteins. Plasticization, i.e. breaking of intermolecular non-covalent bonds, precedes rapid expansion of cuticles but is unnecessary for slow expansion. The compositions of the cuticles and the properties of the proteins are discussed in relation to the expansions which take place in the cuticles.     

Pilgerodendron uviferum（柏科）及其相关类群叶角质层微形态特征的比较研究

在扫描电镜下观察了分布于南半球的柏科Cupressaceae单种属Pilgerodendron u viferum及其相关类群的代表种Austrocedrus chilensis、Libocedrus plumosa和Papuacedr us papuana叶角质层内外表面的微形态特征。发现Pilgerodendron uviferum叶角质层外表面 光滑,不具Florin环,而其余3个属的代表种均有明显的Florin环;且仅L.plumosa叶角质层外 表面有乳状突起。观察结果支持传统的观点,即将P.uviferum作为独立的属;不支持基于DNA 分析的结果,即将P.uviferum归并到Libocedrus属。发现Papuacedrus papuana叶角质层外表 面有许多明显的小凹陷,与其相对应的叶角质层内表面有凹陷的小狭缝,该性状以前未见报 道。     

Stage specific larval,pupal, and adult cuticles in the tracheal system of Sarcophaga bullata

Successive tracheal cuticles of the dorsal longitudinal trunks are studied with the electron microscope. Minor differences seen at the light microscope level are seen as major qualitative and quantitative ones at the ultrastructural level. The larval and pupal cuticles are secreted by similar epithelial cells; these possess large polytene chromosomes. Cell division and possibly cell replacement occur prior to adult cuticle secretion. The findings are discussed in terms of cell specificity, intra- and inter-cellular pattern formation. This simple epithelium, the individual cells of which are capable of producing different cuticles, is interesting since the system is also shown to be responsive to hormone application.     

The relationship between conidial dose,moulting and insect developmental stage on the susceptibility of cotton aphid,Aphis gossypii,to conidia of Lecanicillium attenuatum,an entomopathogenic fungus

The cotton aphid is one of the most serious pests of greenhouse vegetable crops worldwide. It is difficult to control because field populations usually include simultaneously several insect developmental stages. The current research evaluated an isolate (CS625) of Lecanicillium attenuatum, a fungal pathogen of aphids, as to its virulence against different developmental stages of cotton aphid, Aphis gossypii. The influence on mortality of several other factors also was examined: (a) insect moulting, (b) the number of conidia attached to insect cuticles and (c) germination rates of conidia on cuticles of aphids at various developmental stages. Mortality of cotton aphids treated with L. attenuatum conidia varied according to the developmental stage of the host, i.e. the LT_50s with third-instar nymphs and adults was shorter than with first-instar nymphs. The number of spores attached to the surface of first-instar nymphs was approximately one-half of that on third-instar nymphs and adults. Also, the level of spore germination on the surface of first-instar nymphs was lower than on the surface of other stages of the aphid. After moulting, the numbers of conidia attached to new insect cuticles were less than on exuviae. These results suggest that early nymphal stages of cotton aphids may escape fungal disease due, at least in part, to a combination of three factors: low numbers of conidia attached to their cuticles; low levels of conidial germination and rapid ecdyses, which removed conidia before their germ tubes penetrated the host hemolymph.     

分散角质层的分类和命名*

简略讨论了分散角质层对地层学、古生物学和古环境的意义;简述了气孔器的形态学、发生学和形态一发生学的分类;在介绍并讨论了分散角质层的分类原则和命名方法的基础上,提出了新的分类方案.     

Development of plant cuticles: occurrence and role of non-ester bonds in cutin of Clivia miniata Reg. leaves

The effect of BF₃-methanol treatment on the mass and fine structure of isolated Clivia leaf cuticles at different stages of development has been investigated. BF₃-methanol cleaves ester linkages in cutin; however, the cuticles are not completely depolymerized. With increasing age, the residue left after BF₃-methanol treatment increases in mass. In very young cuticles, 10% of the total cutin resisted BF₃-methanol and the fraction of nonester cutin increased up to 62% in mature leaves. Transmission electron microscopy shows that fine structure of the cuticle proper is severely distorted but not destroyed. The internal cuticular layer, which exhibits a heavy contrast when fixed with KMnO₄, is completely depolymerized, while the external cuticular layer is hardly affected. The results are discussed in relation to cuticle development and to the function of cuticles as transpiration resistances.Abbreviation CP cuticle proper - ECL external cuticular layer - E cutin ester bonded cutin - ICL internal cuticular layer - MX-membrane polymer matrix membrane - NE-cutin non-ester bonded cutin - TEM transmission electron microscopy     

Orestovia and the origin of vascular plants

The enigmatic Orestovia from the Lower Devonian of Siberia has a vascular cylinder of spiral and annular tracheids, external and internal cuticles in the cortex, and stomata. Abundant spores are occasionally preserved between the cortex cuticles. The 'reticulate structures' are thyriothecia of a hemisphaeriacean fungus. Spores of several types are found sticking to the cuticle. Orestovia can be conceived as a transitional form between the alga-like Protosalvinia and the sporangiate vascular plants. The origin of land plants is discussed.     

The comparative study on the cuticle micro-morphology of Pilgerodendron uviferum（Cupressaceae） and its relatives

The taxonomic position of the monotypic conifer Pilgerodendron uvi ferum,an endemic species in southern South America,has been disputed on the ba sis of phylogenetic analysis using molecular data. These results suggest that P. u viferum is a species of Libocedrus. Phylogenetic analysis using morphological dat a appears to uphold its separate status. Characters of leaf cuticles are investig ated and compared between four related genera including Pilgerodendron and furth er dis-tinctions between these are reported. The merits of these conflicting dat a sets for the taxonomy of the genus Libocedrus s. l. are discussed. It is conclude d that the evidence for a merger of Pilgeroden-dron with Libocedrus is weak and that both morphology and biogeography support the separation of the two genera.     

Isolation of cuticular membranes from various conifer needles

Summary A method of isolating intact needle cuticles is presented. Cuticles were separated enzymatically from needles of Abies alba Mill., Picea abies (L.) Karst., Picea pungens Engelm., Pinus mugo Turra, and Taxus baccata L. Cuticle separation depended on the enzyme concentration, the developmental stage of the needles and the duration of incubation in the hydrolytic pectinase/cellulase solution. Cuticles could not be removed from needles older than 2 years. Scanning electron micrographs of enzymatically isolated cuticles are presented. The permeance coefficients for water and oxygen transport across the isolated cuticular membranes indicate their functional intactness. But permeance coefficients also show that isolation of cuticular membranes with chromic acid is an unacceptable method, since they are lo longer structurally or functionally intact following isolation by this method.     

Expanding abdominal cuticle in the bug Rhodnius and the tick Boophilus

The abdominal cuticles of Rhodnius prolixus (fifth instar) and Boophilus microplus (adult female) expand dramatically and rapidly during feeding. In the unfed stage of both species the epicuticle of the abdomen is deeply folded, and when rapid stretching takes place the epicuticle unfolds and the underlying procuticle stretches so that the thickness of the cuticle is halved. The cuticles contained only trace amounts of protein soluble in water and aqueous KCl but substantial quantities were extracted with 7 M aqueous urea. The proteins were analysed for their amino acid composition and investigated by gel electrophoresis and isoelectric focusing.In solubility, amino acid composition, molecular weight distribution, and isoelectric points, the proteins isolated from both species resembled one another closely. They had higher molecular weights and higher isoelectric points than did the proteins from flexible, non-stretching cuticles and unlike them had high alanine and histidine and low aspartic acid and glutamic acid contents. Their amino acid composition was very similar to that of the whole cuticle. The proteins were not associated with neutral sugars. Both the Rhodnius and Boophilus cuticles had low chitin contents, 11·2 and 3·8% respectively (on a water-free basis). The composition of the cuticles and the properties of the proteins are discussed in relation to the stretching which they undergo.     

Leaf cuticles behave as asymmetric membranes : evidence from the measurement of diffusion potentials

Cuticles were isolated enzymatically from the leaves of two maple species (Acer saccharum Marsh and A. platanoides L.) and from orange (Citrus aurantium L.). The cuticles were placed in a plastic cuvette and different concentrations of KCl were perfused over the physiological inner and outer surfaces while the electrical potential (E¹⁰) that developed across the cuticles and was caused by ion diffusion was measured. E¹⁰ was always positive, indicating that the permeability of K⁺ was always greater than that of Cl^-. Measured E¹⁰ in cuticles did not fit the Goldman equation, whereas, E¹⁰ measured during KCl diffusion across selected artificial membranes fit the equation. The magnitude of E¹⁰ in cuticles and artificial membranes also was dependent on ionic strength, decreasing as ionic strength increased. These observations are explained by combining classical transport equations with equations that describe the equilibrium ion distribution between ionic double layers in the cuticle or membranes and the bathing solution.     

Gas permeability of plant cuticles

Cuticles from the adaxial surface of Citrus aurantium L. leaves and from the pericarp of Lycopersicon esculentum L. and Capsicum annuum L. were isolated enzymatically and their oxygen permeability was determined. Isolated cuticles were mounted between a gaseous and an aqueous compartment with the physiological outer side of the membrane facing the gaseous compartment. Permeability for oxygen was characterized by permeability (P) and diffusion (D) coefficients. P and D were independent of the driving force (gradient of oxygen concentration) across the cuticle, thus, Henry's law was obeyed. P values for the diffusion of oxygen varied between 3·10^-7 (Citrus), 1.4·10^-6 (Capsicum), and 1.1·10^-6 (Lycopersicon) m·s^-1. Extraction of soluble lipids from the cuticles increased the permeability. By treating the cutin matrix and the soluble lipids as resistances in series, it could be demonstrated that the soluble lipids were the main resistance for oxygen permeability in Citrus cuticles. However, in Lycopersicon and Capsicum, both the cutin matrix and the soluble lipids determined the total resistance. P values were not affected by either the proton concentration (pH 3–9) or the cations (Na⁺, Ca²⁺) present at the morphological inner side of the cuticles. It is concluded that the water content of cuticles does not affect the permeability properties for oxygen. Partition coefficients indicated a high solubility of oxygen in the cuticle of Citrus. The data suggest a solubility process in the cuticle of Citrus with respect to oxygen permeation.Abbreviations CM cuticular membrane - MX cutin polymer matrix - SCL soluble cuticular lipids