植物表皮蜡质参与干旱胁迫的反应机制

植物表皮是植物与外部环境直接接触的部位,包括具有立体网状结构的角质和填充其间并覆盖其上的蜡质。植物在适应外界环境的过程中,表皮蜡质形成了特殊的结构和复杂的化学组成。植物表皮蜡质最重要的功能是参与阻止植物非气孔性失水,提高植物对水分的利用效率,以实现对干旱环境的适应。干旱环境会导致植物表皮蜡质代谢的变化,这种变化最终通过调控基因表达来实现。目前已经发现了多个蜡质代谢相关基因参与了植物对干旱环境的适应,部分基因已经成功克隆并且用于改良农作物的抗旱性。但这些基因参与干旱响应的分子机制及其与ABA的关系并不很清楚。就植物适应水分胁迫而发生的包括蜡质组成和含量在内的代谢变化,以及该过程中所涉及的主要基因及其分子生物学研究进行综述。探讨表皮蜡质在植物适应干旱中的重要作用及其分子机制,可为农作物的抗旱育种提供新型的分子标记和重要靶基因,最终服务于农业生产实践。     

植物角质层内外蜡质的差异及其与抗逆性的关系

植物角质层是覆盖在植物地上部分的叶、花和非木质茎等器官表面的保护层,包括角质和蜡质。其中蜡质根据分布位置不同又分为表皮蜡质和内部蜡质。大量研究表明,表皮蜡质含量和结构在植物生长发育和抗逆性申发挥着重要作用。近年来有研究发现构成蜡质的成分在内外蜡质层中的分布存在差异,角质层蜡质成分影响植物抗逆性。本文针对角质层结构和内外蜡质差异性以及角质层结构和组成与植物抗逆性之间的关系进行了综述。     

植物表皮蜡质对环境胁迫的响应

环境胁迫一直以来是影响植物生长和农作物产量的主要因素,而覆盖植物地上部分最表层的表皮蜡质在植物生长发育、适应外界环境方面起着重要作用。本文综述了近年来国内外在表皮蜡质对环境胁迫响应方面的研究成果,主要体现为对UV、空气湿度、水分、温度和病害等胁迫的抵御作用,并对今后的蜡质研究进行了展望。     

中国干旱半干旱区荒漠植物叶片(或同化枝)表皮微形态特征

为了探讨荒漠植物叶片表皮微形态结构对长期荒漠环境的适应特征及其分类学意义, 应用扫描电镜对中国干旱半干旱荒漠区28科74属117种200多个自然居群的植物叶片(或同化枝)表皮微形态进行了研究。荒漠植物叶(或同化枝)表皮的基本特征是: 表皮附属物相当丰富, 包括大量的表皮绒毛、角质膜蜡质片层或晶体颗粒、表面瘤状或疣状突起以及相对下陷且密度较低的气孔器。对表皮微形态结构及附属物组成进行对比分析, 将荒漠植物粗分为11种基本类型, 包括表皮完全被形态各异的蜡质层或表皮毛覆盖、不同形态类型的表皮毛和蜡质层结合、蜡质层与不同分布类型的气孔器或表皮毛结合, 以及各种突起的表皮细胞与蜡质层的结合等。根据抗逆所依赖的表皮及其附属物微形态结构, 将荒漠植物适应环境胁迫的叶片表皮微形态分为6种主要类型, 它们分别依赖于表皮毛、角质层蜡质、表皮凹凸结构、表面突起、混生的附属物以及上下表皮异化特征。荒漠植物叶表皮微形态结构的适应特征是通过表皮附属物(绒毛和角质膜蜡质层)与表皮结构(凹凸、乳突和气孔器)的相互协调作用, 共同抵御强光、降低叶片的蒸腾来提高植物对干旱等不利环境的抗性。该研究在一定程度上阐明了荒漠植物对逆境的适应机理及其演化趋势, 并为优良固沙植物的筛选提供了理论依据。     

植物表皮蜡质生物合成及调控

植物表皮蜡质,是覆盖在陆地植物地上部分表面的一层疏水性脂类物质,是植物应对外界环境变化的第一道屏障,在抑制植物水分非气孔散失及保护植物免受病虫害入侵、紫外线辐射等方面起着重要作用。综述了近年来表皮蜡质在生物合成及调控等方面的研究进展,并对研究中存在的问题及研究前景进行了展望。     

植物蜡质及其与环境的关系

陆生植物的地上部分如叶、茎、花、果实等的表面覆盖着一层蜡质,它是由一系列复杂化合物组成的具有三维微结构的疏水层,在植物生长和发育过程中起着不可或缺的作用,具有很好的生物学功能。作为植物与环境的第一接触面,蜡质对外界环境因子的响应较敏感,当植物受到外界不利环境因子胁迫时,蜡质会改变自身晶体结构形态或化学组分构建防御机制以减少胁迫因子的作用,有效地协调植物与环境的关系。综述了近年来国内外关于植物蜡质的研究进展,在阐述蜡质层结构及其化学组分的基础上,着重介绍植物与环境因子的作用,包括非生物环境因子如水分、温度、光照、环境污染等以及植食性昆虫和病原菌等生物环境因子的作用。研究显示,胁迫环境下植物蜡质化学组分的变化,是由于不利环境因子的作用足以改变蜡质各产物的合成途径,从而影响蜡质产物。植物蜡质利用各种生理、化学机制对胁迫环境因子的适应以及响应,是植物适应各种生境的基础,因此通过对植物蜡质与环境关系的研究为进一步解析植物与环境关系提供证据。     

小麦蜡质的逆境胁迫

蜡质是植物与外部环境的界面,对植物具有重要的生物学意义。本文综述了小麦叶表皮蜡质的物理结构、化学成分及小麦蜡质在不同逆境胁迫下的变化。     

植物超长链脂肪酸及角质层蜡质生物合成相关酶基因研究现状

超长链脂肪酸(very long chain fatty acids, VLCFAs)在生物体中具有广泛的生理功能, 它们参与种子甘油酯、生物膜膜脂及鞘脂的合成, 并为角质层蜡质的生物合成提供前体物质。角质层是覆盖在植物地上部分最表层的保护层, 由角质和蜡质组成, 其中蜡质又分为角质层表皮蜡和内部蜡, 在植物生长发育、适应外界环境方面起重要作用。VLCFAs的合成由脂肪酰-CoA延长酶催化, 该酶是由b-酮脂酰-CoA合酶、b-酮脂酰-CoA还原酶、b-羟脂酰-CoA脱水酶和反式烯脂酰-CoA还原酶组成的多酶体系。合成后的VLCFAs通过脱羰基与酰基还原作用进入角质层蜡质合成途径, 形成各种蜡质组分。文章就VLCFAs及角质层蜡质合成代谢途径中相关酶基因研究进展方面做了综述, 并对植物蜡质基因研究中存在的问题提出一些看法。     

28种柳属植物的叶表皮微形态特征及其分类学意义

对28种表型相似、种间界限模糊的柳属植物在扫描电子显微镜下的叶表皮微形态特征进行观察,结果表明:柳属中有7种角质层蜡质纹饰,分别是平滑蜡质层、壳状蜡质层、痂状蜡质层、片状晶体、膜片状晶体、锥形纤维体和鳞片状纤维体,其中锥形纤维体和鳞片状纤维体为柳属所特有,而片状晶体和膜片状晶体为首次在柳属植物中发现;扫描电子显微镜下柳属植物叶表皮毛被的微观形态特征并不似其宏观形态(疏毛、绢毛、绒毛等)那样具有显著差异,微观形态主要表现为毛被密度、长短和卷曲方式(分为直,微弯曲和深度卷曲三种)的不同.研究表明叶表皮蜡质纹饰类型、气孔器的形态等微形态特征较为稳定,对柳属植物中表型相似的种类有很好的鉴定价值,但对组、亚属水平的界定作用不大;分布于寒冷地区和高海拔地区的柳属植物的叶表皮微形态特征相对多样,这可能是植物对寒冷环境的适应进化.     

植物叶表面的附着物

植物叶表面上的附着物实际上是植物叶表面的分泌物。很多物质可以从原生质体中分离并沉积下来,这实际上是一种分泌过程,这些沉积物质就是分泌物。叶表皮细胞外壁上附着的角质膜、蜡质以及各种盐的     

Δ12-脂肪酸去饱和酶基因(fad2)突变对油菜叶片表面结构和透性的影响

首次报告了利用简单的叶片氧化实验可区别油菜正常株系及具有高油酸(低亚油酸)性状的fad2基因(Δ12-fatty acid desaturase gene)突变体。突变体叶片内的有色或具还原性的物质能被次氯酸钠及硝酸银溶液在5-10min漂白或氧化,正常株系及突变体的fad2基因功能补偿转化体的叶片被漂白的时间需要24-48h。通过扫描电镜观察揭示了突变体与正常株系之间叶片表面蜡颗粒沉积均匀性上的差异。实验结果表明：fad2基因的突变改变了叶片表面蜡的沉积结构并增大了叶片表层的溶液渗透性,其原因可能与木质(cutan)的合成受抑制相关。     

Composition differences between epicuticular and intracuticular wax substructures: how do plants seal their epidermal surfaces?

The protective wax coating on plant surfaces has long been considered to be non-uniform in composition at a subcellular scale. In recent years, direct evidence has started to accumulate showing quantitative compositional differences between the epicuticular wax (i.e. wax exterior to cutin that can be mechanically peeled off) and intracuticular wax (i.e. wax residing within the mechanically resistant layer of cutin) layers in particular. This review provides a first synthesis of the results acquired for all the species investigated to date in order to assign chemical information directly to cuticle substructures, together with an overview of the methods used and a discussion of possible mechanisms and biological functions. The development of methods to probe the wax for z-direction heterogeneity began with differential solvent extractions. Further research employing mechanical wax removal by adhesives permitted the separation and analysis of the epicuticular and intracuticular wax. In wild-type plants, the intracuticular (1-30 μg cm(-2)) plus the epicuticular wax (5-30 μg cm(-2)) combined to a total of 8-40 μg cm(-2). Cyclic wax constituents, such as triterpenoids and alkylresorcinols, preferentially or entirely accumulate within the intracuticular layer. Within the very-long-chain aliphatic wax components, primary alcohols tend to accumulate to higher percentages in the intracuticular wax layer, while free fatty acids and alkanes in many cases accumulate in the epicuticular layer. Compounds with different chain lengths are typically distributed evenly between the layers. The mechanism causing the fractionation remains to be elucidated but it seems plausible that it involves, at least in part, spontaneous partitioning due to the physico-chemical properties of the wax compounds and interactions with the intracuticular polymers. The arrangement of compounds probably directly influences cuticular functions.     

Chemical composition of the Prunus laurocerasus leaf surface. Dynamic changes of the epicuticular wax film during leaf development

The seasonal development of adaxial Prunus laurocerasus leaf surfaces was studied using newly developed methods for the mechanical removal of epicuticular waxes. During epidermal cell expansion, more than 50 microg leaf(-1) of alkyl acetates accumulated within 10 d, forming an epicuticular wax film approximately 30 nm thick. Then, alcohols dominated for 18 d of leaf development, before alkanes accumulated in an epicuticular wax film with steadily increasing thickness (approximately 60 nm after 60 d), accompanied by small amounts of fatty acids, aldehydes, and alkyl esters. In contrast, the intracuticular waxes stayed fairly constant during development, being dominated by triterpenoids that could not be detected in the epicuticular waxes. The accumulation rates of all cuticular components are indicative for spontaneous segregation of intra- and epicuticular fractions during diffusional transport within the cuticle. This is the first report quantifying the loss of individual compound classes (acetates and alcohols) from the epicuticular wax mixture. Experiments with isolated epicuticular films showed that neither chemical conversion within the epicuticular film nor erosion/evaporation of wax constituents could account for this effect. Instead, transport of epicuticular compounds back into the tissue seems likely. Possible ecological and physiological functions of the coordinate changes in the composition of the plant surface layers are discussed.     

Direct Access to Plant Epicuticular Wax Crystals by a New Mechanical Isolation Method

A new method for the isolation of wax crystals from plant surfaces is presented. The wax-covered plant surface, e.g., a piece of a leaf or fruit, is brought into contact with a preparation liquid, e.g., glycerol or triethylene glycol, and cooled to ca. -100 degrees C. When the plant specimen is removed, the epicuticular wax remains embedded in the frozen liquid. After it warms up, the wax layer can be captured on appropriate carriers for further studies. This isolation method causes very little stress on the wax crystals; thus the shape and crystal structure are well preserved. In many cases it is possible, by choosing a preparation liquid with appropriate wettability, to isolate either the entire epicuticular wax layer or only discrete wax crystals without the underlying wax film. These crystals are well suited for electron diffraction studies by transmission electron microscopy and high resolution imaging by atomic force microscopy. The absence of intracuticular components and other impurities and the feasibility of the selective isolation of wax crystals enable improved chemical analysis and a more detailed study of their properties.     

Epicuticular wax structures on stems and comparison between stems and leaves – A survey

The cuticle, forming the outermost layer of plant tissues and being in direct contact with the environment, consists of waxes and cutin. Waxes are hydrophobic substances that are divided in two groups: intra- and epicuticular, depending on their localisation. Epicuticular waxes appear as smooth coverings, however, many plants also produce superimposed wax structures of a crystalline nature. While studies of waxes have almost exclusively focused on leaves, here a survey of epicuticular wax structures on stems is presented. The stem surface of 343 higher plant taxa, representing 80 families, was examined using scanning electron microscopy. The adaxial and abaxial surfaces of leaves of 319 taxa were also examined to determine the relationship between wax structures on stems and leaves. Wax structures are classified, described and discussed. The results of the study indicate that stems exhibit the same main wax crystal types that have been described for leaves. Seventy percent of the examined taxa produced wax crystals on their stems. In ∼24% of the taxa, wax crystals were absent on leaves and found only on stems. In plant taxa that produce wax crystals, 40% exhibit the same type on either side of their leaves and on their stem. However, a much stronger morphological similarity exists between crystal shapes present on the adaxial and abaxial surfaces of leaves than between those present on the stem and those on leaves. In general, these observations suggest that stems are quite different than leaves in terms of their epicuticular wax structures.     

Oviposition by Plutella xylostella (Lepidoptera: Plutellidae) and effects of phylloplane waxiness

Three approaches were used to investigate effects of host plant epicuticular waxes on oviposition site selection by Plutella xylostella (L.). In the first approach, oviposition on canola (Brassica napus L.) that had epicuticular wax reduced by application of a carbamate herbicide (S-ethyl dipropylthiocarbamate) was compared with oviposition on untreated control plants. A second approach compared oviposition on sibling strains of B. napus with different wax blooms (glossy and waxy), and a third approach compared oviposition by P. xylostella on parafilm that had been applied to glossy and waxy B. napus strains for transfer of leaf components. Significantly more eggs were deposited on herbicide-treated plants (with reduced epicuticular wax) than on untreated controls. Similarly, more eggs were deposited on glossy than on waxy sibling strains of B. napus. In parafilm assays significantly more eggs were deposited on treated than on untreated parafilm. Several mechanisms could explain the differences in attractiveness of surfaces with varying wax content as oviposition sites for P. xylostella, including visual, chemical, and tactile differences between substrates. These mechanisms are discussed.     

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。     

Spruce budworm feeding and oviposition are stimulated by monoterpenes in white spruce epicuticular waxes

Monoterpenes, source of the distinctive odor of conifers, are generally considered plant defensive compounds. However, they are also known to act as long‐range insect attractants, as they are volatile and permeate forest airspaces. Moreover, they are lipid soluble and can be absorbed into plant epicuticular waxes. We test their role in short‐range host plant choice by both adult females and larvae of a folivorous forest pest (Choristoneura fumiferana). We conducted laboratory assays testing the responses of Eastern spruce budworm to an artificial monoterpene mix (α‐pinene, β‐pinene, limonene, myrcene) and to white spruce (Picea glauca) epicuticular waxes in closed arenas. Ovipositing females preferred filter paper discs treated with P. glauca waxes to controls, and preferred the waxes + monoterpenes treatment to waxes alone. However, females showed no preference between the monoterpene‐treated disc and the control when presented without waxes. Feeding larvae prefered wax discs to control discs. They also consumed discs treated with realistic monoterpene concentrations and wax preferentially over wax‐only discs, but showed no preference between extremely high monoterpene concentrations and wax‐only controls. In an insect‐free assay, P. glauca epicuticular wax decreased monoterpene volatilization. These results suggest that P. glauca waxes and realistic concentrations of monoterpenes are stimulatory to both egg‐laying females and feeding larvae, and that their effects are synergistic.