Phase behaviour and crystallinity of plant cuticular waxes studied by Fourier transform infrared spectroscopy

The phase behaviour of cuticular waxes from leaves of Hedera helix L. and Juglans regia L. was studied by Fourier transform infrared spectroscopy. For this purpose reconstituted waxes, isolated cuticular membranes, dewaxed polymer matrix membranes and whole leaves were studied in the horizontal attenuated total reflection and transmission modes. Melting curves of cuticular waxes were derived from temperature-dependent changes in the absorption maximum of the symmetric stretching mode of CH₂ groups (ν_s, at approx. 2856–2848 cm⁻¹). With increasing temperature absorption band doublets due to CH₂ scissoring (δ_sciss) and rocking (δ_rock) movements (at approx. 1473–1471 and 730–720 cm⁻¹, respectively) indicative of an orthorhombic arrangement of alkyl chains merged into a single peak. The area ratio of the peaks at approx. 720 and 730 cm⁻¹ was used as a measure for aliphatic crystallinity of plant cuticular waxes at a given temperature. The investigations of reconstituted cuticular waxes and those still embedded in isolated cuticles or in situ on the leaf produced comparable results. The findings are discussed in terms of the properties of the cuticular transport barrier. Received: 21 March 1997 / Accepted: 25 April 1997     

植物角质层蜡质的化学组成研究综述

角质层是植物与外界的第一接触面,而角质层蜡质则是由位于角质层外的外层蜡质和深嵌在角质层中的内层蜡质两部分构成。植物角质层蜡质成分极其复杂,具有重要的生理功能。综述了有关植物角质层蜡质的化学组成信息,探讨了目前植物角质层蜡质化学成分研究中存在的一些问题,展望了角质层蜡质成分的研究前景。     

Epicuticular waxes of albino maize

Epicuticular wax of albino maize seedlings contains alkanes (9.5 %), esters (23.3 %), aldehydes (14.1 %) and free alcohols (53.1 %). The wax compositio     

Ecophysiology of cuticular transpiration: comparative investigation of cuticular water permeability of plant species from different habitats

Water permeabilities of astomatous, isolated cuticular membranes (CM) of 24 different plants species were measured. Permeances 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) among different plant species, thus covering a range of over 2 orders of magnitude. Ranking of species according to permeances resulted in four distinct groups. The first group, of species with the lowest cuticular transpiration rates, included evergreen species growing in warm dry tropical climates (e.g. Vanilla planifolia and Monstera deliciosa leaves). The second class, with slightly higher water permeabilities, included evergreen species with typical scleromorphic leaf properties, adapted to a typical mediterranean type of climate with a dry period during the year (e.g. Citrus limon and Olea europaea leaves). The third group of species, where the highest leaf cuticular transpiration rates were observed, included deciduous species normally growing in a tempeate climate (e.g. Juglans regia and Forsythia suspensa leaves). Fruit cuticular membranes (CM) made up the fourth group (e.g. Capsicum annuum and Malus cf. domestica fruits), with even higher permeances than leaves of species from group 3. Thus, it appears that the plant species investigated show ecophysiological adaptations to the climatic demands of their natural habitats in cuticular water permeability.     

Characterization of an alkylresorcinol synthase that forms phenolics accumulating in the cuticular wax on various organs of rye (Secale cereale)

Alkylresorcinols are bioactive compounds produced in diverse plant species, with chemical structures combining an aliphatic hydrocarbon chain and an aromatic ring with characteristic hydroxyl substituents. Here, we aimed to isolate and characterize the enzyme that forms the alkylresorcinols accumulating in the cuticular wax on the surface of all above‐ground organs of rye. Based on sequence homology with other type‐III polyketide synthases, a candidate alkylresorcinol synthase was cloned. Yeast heterologous expression showed that the enzyme, ScARS, is highly specific for the formation of the aromatic resorcinol ring structure, through aldol condensation analogous to stilbene synthases. The enzyme accepts long‐chain and very‐long‐chain acyl‐CoA starter substrates, preferring saturated over unsaturated chains. It typically carries out three rounds of condensation with malonyl‐CoA prior to cyclization, with only very minor activity for a fourth round of malonyl‐CoA condensation and cyclization to 5‐(2′‐oxo)‐alkylresorcinols or 5‐(2′‐hydroxy)‐alkylresorcinols. Like other enzymes involved in cuticle formation, ScARS is localized to the endoplasmic reticulum. ScARS expression patterns were found correlated with alkylresorcinol accumulation during leaf development and across different rye organs. Overall, our results thus suggest that ScARS synthesizes the cuticular alkylresorcinols found on diverse rye organ surfaces.     

Changes in leaf cuticular waxes of sesame (Sesamum indicum L.) plants exposed to water deficit

Sesame (Sesamum indicum L.) is one of the most important oilseed crops, having seeds and oil that are highly valued as a traditional health food. The objective of this study was to evaluate leaf cuticular wax constituents across a diverse selection of sesame cultivars, and the responses of these waxes to drought-induced wilting. Water-deficit was imposed on 18 sesame cultivars by withholding irrigation for 15d during the post-flowering stage, and the effect on seed yield and leaf waxes compared with a well-watered control. Leaf cuticular waxes were dominated by alkanes (59% of total wax), with aldehydes being the next-most abundant class. Compared to well-irrigated plants, drought treatment caused an increase in wax amount on most cultivars, with only three cultivars having a notable reduction. When expressed as an average across all cultivars, drought treatment caused a 30% increase in total wax amount, with a 34% increase in total alkanes, a 13% increase in aldehydes, and a 28% increase in the total of unknowns. In all cultivars, the major alkane constituents were the C27, C29, C31, C33, and C35 homologs, whereas the major aldehydes were the C30, C32, and C34 homologs, and drought exposure had only minor effects on the chain length distribution within these and other wax classes. Drought treatments caused a large decrease in seed yield per plant, but did not affect the mean weight of individual seeds, showing that sesame responds to post-flowering drought by reducing seed numbers, but not seed size. Seed yield was inversely correlated with the total wax amount (-0.466*), indicating that drought induction of leaf wax deposition does not contribute directly to seed set. Further studies are needed to elucidate the ecological role for induction of the alkane metabolic pathway by drought in regulating sesame plant survival and seed development in water-limiting environments.     

Stomatal behaviour and cuticular properties of maize leaves of different chilling-resistance during cold treatment

Stomatal behaviour and the amount and synthesis of epicuticular waxes were studied in maize leaves of various degrees of chilling resistance in order to investigate the rapid desiccation characteristic of chilling injury. In contrast to the resistant variety (KSC 360), the sensitive line (Lye) failed to close the stomata during chilling treatment. Both, the amount of epicuticular waxes and their degree of labeling by 1-14C-acetate were much higher in the resistant than in the sensitive leaves. Chilling-sensitivity was also related to a suppressed conversion of free fatty acids into free primary alcohols.     

空气湿度与土壤水分胁迫对紫花苜蓿叶表皮蜡质特性的影响

选用2个抗旱性不同的紫花苜蓿品种,敖汉(强抗旱)和三得利(弱抗旱),设置空气湿度(45%-55%和75%-85%)和土壤水分胁迫(75%和35%田间持水量)处理,分析紫花苜蓿叶表皮蜡质含量、组分及晶体结构、气体交换参数、水势及脯氨酸含量的变化规律。结果表明,单独土壤水分胁迫时,紫花苜蓿叶表皮蜡质晶体结构及蜡质总量无显著变化;敖汉蜡质组分中烷类、酯类含量增加,醇类含量下降;三得利醇类含量下降,烷类、酯类含量变化不显著。低空气湿度胁迫时,两品种蜡质总量无显著变化,烷类和酯类含量显著增加,醇类含量显著下降,叶表皮片状蜡质晶体结构熔融呈弥漫性,扩大了对叶表面积的覆盖,其蒸腾速率显著低于正常湿度。复合胁迫处理时,叶表皮片状蜡质晶体结构继续呈弥漫性,烷类、酯类、未知蜡质组分含量均高于单独胁迫处理,醇类含量最低,而蜡质总量除三得利显著高于对照外,其余均无显著差异。紫花苜蓿叶表皮蜡质各组分含量(除醇类)及蜡质总量与光合速率呈显著负相关,与蒸腾速率无显著相关关系。蜡质总量与叶水势呈显著正相关。总体上,敖汉蜡质总量显著高于三得利,蜡质组分中烷类物质的增加有助于提高植株的抗旱性。在复合胁迫下,强抗旱品种主要通过气孔因素控制水分散失,而弱抗旱品种通过气孔和非气孔因素共同控制植物水分散失。     

植物逆境胁迫抗性的功能基因组研究策略

植物对逆境胁迫抗性的功能基因组研究主要是寻找胁迫抗性位点在相关物种基因组中的保守位置,发现胁迫反应中的高度保守序列,确定植物胁迫反应的调控机理,进而得到植物对逆境胁迫抗性的关键代谢途径和其中的关键调控因子,为进一步选择用于改良植物对逆境胁迫抗性的关键基因奠定基础。本文从主要模式植物(苔藓类植物、复苏植物、盐土植物和甜土植物)、主要技术策略(基因的差异表达分析、基因表达序列标签、cDNA芯片技术。基因表达序列分析和基因敲除和突变体筛选分析)和生物信息学方法(数据分析的生物信息学方法设计到序列比较、比较基因组学、电子克隆)等三个方面对国内外植物逆境胁迫抗性的功能基因组研究策略作了全面综述。     

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.     

丛枝菌根对植物根际逆境的生态学意义

近年来,我国在菌根分子生物学、菌根营养学、菌根分类学和菌根生态学等方面取得了令人瞩目的研究成果,其中对丛枝菌根真菌(AMF)的研究居多。AMF能与大部分陆地植物根系形成共生关系,促进植物生长发育,提高植物抗逆性,在保持生态平衡、保护生态环境等方面发挥重要作用。本文主要从非生物胁迫(干旱胁迫、重金属污染、盐碱胁迫)和生物胁迫(致病菌和线虫侵染)方面介绍了AMF在植物根际逆境中发挥的生态功能及作用机制,提出了该研究领域尚存的不足之处和研究前景,为AMF后续研究提供参考。     

miR398在植物逆境胁迫应答中的作用

MicroRNA (miRNA)是一类新型的调控基因表达的小分子RNA, 它作为基因表达的负调控因子, 在转录后水平调节靶基因的表达。miRNA参与调控植物的生长发育, 并在多种非生物与生物胁迫响应中发挥重要作用。miR398是第一个被报道的受氧化胁迫负调控的miRNA。它通过负调控其靶基因Cu/Zn过氧化物歧化酶(Cu/Zn-superoxide dismutase, CSD)的表达, 在多种逆境胁迫响应中扮演重要角色, 如调节铜代谢平衡, 应答重金属、蔗糖、臭氧等非生物胁迫, 以及参与应答生物胁迫等。文章综述了miR398在多种逆境胁迫响应中重要的调节作用及miR398自身的转录调控。     

The effects of Kloeckera apiculata on the cuticular waxes of navel orange fruit

Kloeckera apiculata 34-9 was selected from the rhizosphere soil for its high efficacy in controlling citrus green and blue mold. In this study, the effect of the antagonistic yeast K. apiculata on citrus cuticular wax was investigated in ripening Newhall navel orange (Citrus sinensis L. Osbeck). Our results show that K. apiculata triggers the production of cuticular waxes and surface wax morphology changes in the fruit surface. 15 K. apiculata-responsive differentially expressed genes (DEGs) were identified for wax metabolism by using the Affymetrix citrus genome GeneChip. Using GC–MS, 46 wax compounds were found in the Newhall fruit surface. On one hand, esters including docosanoic acid, 1,2,3-propanetriyl ester and 9-hexadecenoic acid, 9-octadecenyl ester were up-regulated approximately twofold in the treatment condition compared with the control; and on the other hand, the fatty acids and fatty alcohols decreased by 74.4% and 72.3%, respectively, in the treatment condition. The new wax production and increased hydrophobicity of the Newhall surface resulting from the treatment may influence spore adhesion and germination. Furthermore, the response of the fruit waxes to the K. apiculata stimulus is likely to be regulated by intra-cellular H₂O₂ signaling. This study demonstrated the response fruit waxes to K. apiculata in Newhall navel oranges, thus providing new clues that aid our understanding of the mechanisms of action of antagonistic yeasts in postharvest fruits.     

Structures and molecular dynamics of plant waxes

Waxes from the leaves of Fagus sylvatica L. (European beech tree) and Hordeum vulgare L. (barley) have been investigated using NMR, DSC, X-ray diffraction and gas chromatographic methods. The wax from Fagus sylvatica, consisting mainly of n-alkanals, n-alkanes and 1-alkanols, has chain-lengths ranging from 20 to 52 carbon atoms with an average chain-length of 30.5 carbon atoms. The X-ray results show that the wax is to a large extent ( 70%) amorphous. The wax from the leaves of Hordeum vulgare L., consisting mainly of n-alkanols, has chain-lengths ranging from 20 to 50 carbon atoms with an average chain-length of 27.4 carbon atoms. The wax is 52% crystalline. It seems that the structure of this wax differs from those of other plant waxes that have been investigated in that the longer chains bridge the amorphous zone between two adjacent layers of crystalline material, thus linking the two layers. This linking affects the melting point of the wax noticeably. The activation energies for the different molecular motions in these waxes have been extracted from the NMR spin-lattice relaxation time measurement. Correspondence to: E. C. Reynhardt     

Composition of sugarcane waxes in rum factory wastes

Wastes produced during fermentation and distillation of crude sugarcane juice in rum factories were evaluated as a new source of waxes. The chemical composition of the crude wax extracted from adsorbat of the wastes on fuller's earth was studied by GC-mass spectrometry. Series of linear alkanes (C19-C33), and wax esters constitute the main components. In addition, phytosterols, triterpene methyl ethers, ethyl and methyl esters of fatty acids, and free fatty acids were found as minor components. Acid (predominance of C16 and C18) and alcohol portions (C26-C32) of the wax esters were analysed after saponification.     

小麦品系CP98(11)不同器官表皮蜡质组分和蜡质晶体结构的差异分析

为明确小麦不同器官表皮蜡质晶体结构和蜡质组分的差异,该研究以小麦品系CP98(11)为材料,在小麦扬花期分别取小麦的旗叶、叶鞘、穗下茎、花药和颖壳,利用气相色谱技术对各器官表皮蜡质组分进行鉴定,并通过扫描电镜观察其蜡质晶体结构。结果表明:(1)小麦不同器官的蜡质成分共鉴定出30种,主要为初级醇、二酮、烷烃、脂肪醛、脂肪酸、酯。(2)叶鞘、穗下茎、颖壳的蜡质中二酮含量最高,分别占蜡质总量的78.96%、67.03%和68.6%;花药的蜡质中烷烃含量最高(75.82%);旗叶的蜡质中初级醇含量最高(45.91%),其次为烷烃33.19%。(3)扫描电镜观察显示,旗叶正面的蜡质晶体呈片状结构,旗叶反面和颖壳的蜡质晶体结构呈片状与柱状混合的结构,花药的蜡质呈明显的波浪状结构,穗下茎和叶鞘的蜡质晶体呈柱状结构。     

植物MYB转录因子与非生物胁迫响应研究

MYB转录因子家族是植物中最大的转录因子家族之一,在植物体内的多种生理生化反应中起着关键性作用,其中一项重要功能就是对非生物逆境的应答。这类转录因子通过调控生长发育,影响代谢产物的合成和影响激素信号等多方面参与非生物逆境的应答。介绍了MYB转录因子的结构特点和分类上的新发现,并综述了近几年MYB转录因子家族在植物响应干旱、高温、低温和高盐等非生物胁迫方面的研究进展。     

Functional morphology of the cuticular terraces in burrowing terrestrial brachyuran decapods

Observations on Gecarcinus lateralis and Ocypode quadrata from Bermuda show that their cuticular terraces are not functional as burrowing sculptures, as previously assumed. Instead, they increase the friction against the walls of the burrow when the animal wedges itself to avoid being extracted by predators. No significant increase in the number of terraces takes place during growth in the size interval available for this study. This is different from the situation described as usual in burrowing decapods, and is rather similar to that of crevice-dwelling crabs. The distribution of terraces and their ontogenetic pattern, therefore, are not reliable indicators of the life habits.