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。     

植物角质层基因研究进展

角质层是形成于陆生植物表皮细胞壁外表面的脂质保水层。角质层的基本功能是保水,同时也在响应逆境胁迫、自我清洁及器官发育等方面发挥作用。角质层通常由角质和蜡质组成。角质是角质层的主要结构成分,其主要组分是聚酯。蜡质成分主要为极长链饱和脂肪酸及其衍生物。这些组分在内质网上合成后被转运到细胞表面,进一步形成完整的角质层结构。近年来通过对角质层相关突变体及相应基因的研究,人们对角质层在合成、转运、形成及调控等各个阶段都有了较为深入的认识。蜡质和角质的合成途径已在角质层相关基因功能的解释下逐渐浮出水面。有关角质层前体转运方面的研究,主要的突破在于ABCG全转运蛋白的发现和功能解析。在角质层形成的机理方面,角质层基因中的酯酶和脂酶类基因的研究有助于进一步认识这个复杂的过程。在基因调控方面,新的转录因子基因和角质层与环境之间的相互关系研究,也为已知的调控网络增加了新内容。该文综述了目前关于角质层相关基因的最新研究进展。     

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。     

植物表皮蜡质与抗旱及其分子生物学

植物表皮蜡质是覆盖在植物最外层的一类有机混合物总称,它是植物自我防护的最后一道屏障,在植物生长发育过程中起重要作用。文章就植物表皮蜡质的成分、转运、晶体的形成和发育、形态结构以及环境变化对表皮蜡质的影响,特别是在蜡质与角质蒸腾、叶片水分利用效率和产量的关系以及蜡质的生理作用和合成过程的分子生物学研究进展方面做了系统综述,并对植物蜡质研究中存在的问题做了探讨。     

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。     

麦冬、土麦冬和阔叶土麦冬叶表皮形态结构的观察

用光镜和扫描电镜观察了麦冬（Ophiopogon japonicus（L．f）Ker—Gawl.]、土麦冬（Liriope spicata Lour．）和阔叶土麦冬（L．platyphylla Wanget Tang）叶表皮显微结构、亚显微结构和角质层内表面的形态结构。结果表明,气孔主要分布于麦冬、土麦冬和阔叶土麦冬叶片的下表皮,气孔密度分别为76．4、114．3和99．8个·mm^-2;仅阔叶土麦冬叶片上表皮有少量气孔分布。3种植物的气孔器均不具有副卫细胞,并在叶脉间形成纵向气孔带。表皮细胞长方形,气孔带与非气孔带处表皮细胞的形态和大小差异较明显。麦冬气孔周围的表皮细胞平周壁具明显瘤状突起,导致气孔下陷;土麦冬气孔周围的表皮细胞平周壁呈波浪状突起,使气孔相对下陷;阔叶土麦冬气孔周围的表皮细胞平周壁基本无突起,气孔不下陷。3种植物的叶表皮均有发达的角质层和丰富的蜡质,且蜡质主要分布于下表皮气孔带处。这些结构特征可能与它们所具有的喜阳、耐阴和耐旱等特性有一定的相关性。     

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.     

云南禄劝中泥盆世晚期角质残植煤中植物角质层的再研究

通过光学、扫描电子和透射电子显微镜观察,对云南禄劝中泥盆世晚期角质残植煤层中的植物角质层进行再研究。禄劝的植物角质层定为Orestoviacf.devonica Ergolskaya,1936,具有两种类型:类型Ⅰ,角质层具有规则分布的孔状结构,分布密度为40—45个/mm2,表皮细胞呈不规则多边形或长条形;类型Ⅱ,角质层规则分布似气孔结构,分布密度为50—60个/mm2,表皮细胞呈长方形。根据大植物化石研究,结合生物地层资料,云南禄劝的植物角质残植煤层的成煤时代为中泥盆世晚期(late Givetian)。基于对当时古地理和古气候分析,云南禄劝角质残植煤层的形成主要受控于当时区域古地理环境及其局部古气候条件。     

核盘菌侵染对拟南芥表皮蜡质结构及化学组成的影响

以野生型拟南芥与蜡质突变体cer1、cer4为试验材料,通过研究核盘菌胁迫对拟南芥茎表皮蜡质结构及组分含量的影响,揭示核盘菌侵染与表皮蜡质的关系。扫描电镜结果显示,野生型拟南芥蜡质晶体以垂直于表面的杆状、块状结构为主;突变体cer1晶体类型以水平的松针状、块状结构为主;突变体cer4蜡质晶体以垂直片层结构为主。核盘菌胁迫下,拟南芥蜡质晶体结构及分布形态发生变化。蜡质层结构在核盘菌胁迫下表现为:杆状、松针状蜡质晶体减少—蜡质晶体熔融—表皮"囊状凸起"—表皮膜层破裂。这些结构变化有利于病菌突破角质层屏障而侵入到植株体内。色质谱分析结果显示:与野生型相比,cer1突变体烷、次级醇、酮类显著减少;cer4突变体表现为一级醇含量减少。接种核盘菌后,野生型拟南芥与蜡质突变体一级醇类显著增加(cer1增加不显著);烷类、次级醇类、酮类含量与蜡质总量均显著减少,表明蜡质前体物质在受到核盘菌胁迫后更多地通过酰基还原途径生成一级醇,从而减少了由脱羰基途径所生成的蜡质组分。核盘菌通过改变表皮蜡质晶体结构与化学组分分泌量来促进侵染。     

植物角质层蜡质合成与调控的分子生物学研究进展

角质层覆盖于陆生植物的地上部分。沉积于其表面的外角质层蜡质组成了植物与外部环境之间的屏障。蜡质的合成是由大量酶类协同作用的结果,又是一个积极可调控的过程。综述了近年来角质层蜡质合成与调控的分子生物学研究进展,包括突变体筛选、基因克隆和鉴定,以及功能基因组学研究等三方面,并对植物蜡质代谢基因克隆鉴定中存在的问题进行了探讨。     

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.     

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.     

Chemical composition of the epicuticular and intracuticular wax layers on the adaxial side of Ligustrum vulgare leaves

Previous research has shown that cuticular triterpenoids are exclusively found in the intracuticular wax layer of Prunus laurocerasus. To investigate whether this partitioning was species-specific, the intra- and epicuticular waxes were identified and quantified for the glossy leaves of Ligustrum vulgare, an unrelated shrub with similar wax morphology. Epicuticular wax was mechanically stripped from the adaxial leaf surface using the adhesive gum arabic. Subsequently, the organic solvent chloroform was used to extract the intracuticular wax from within the cutin matrix. The isolated waxes were quantified using gas chromatography with flame ionization detection and identified by mass spectrometry. The results were visually confirmed by scanning electron microscopy. The outer wax layer consisted entirely of homologous series of very-long-chain aliphatic compound classes. By contrast, the inner wax layer was dominated (80%) by two cyclic triterpenoids, ursolic and oleanolic acid. The accumulation of triterpenoids in the intracuticular leaf wax of a second, unrelated species suggests that this localization may be a more general phenomenon in smooth cuticles lacking epicuticular wax crystals. The mechanism and possible ecological or physiological reasons for this separation are currently being investigated.     

Mutation in Wilted Dwarf and Lethal 1 (WDL1) causes abnormal cuticle formation and rapid water loss in rice

Epidermal cell layers play important roles in plant defenses against various environmental stresses. Here we report the identification of a cuticle membrane mutant, wilted dwarf and lethal 1 (wdl1), from a rice T-DNA insertional population. The muant is dwarf and die at seedling stage due to increased rates of water loss. Stomatal cells and pavement cells are smaller in the mutant, suggesting that WDL1 affects epidermal cell differentiation. T-DNA was inserted into a gene that encodes a protein belonging to the SGNH subfamily, within the GDSL lipase superfamily. The WDL1–sGFP signal coincided with the RFP signal driven by AtBIP–mRFP, indicating that WDL1 is an ER protein. SEM analyses showed that their leaves have a disorganized crystal wax layer. Cross-sectioning reveals loose packing of the cuticle and irregular thickness of cell wall. Detailed analyses of the epicuticular wax showed no significant changes either in the total amount and amounts of each monomer or in the levels of lipid polymers, including cutin and other covalently bound lipids, attached to the cell wall. We propose that WDL1 is involved in cutin organization, affecting depolymerizable components.     

植物角质层对非生物逆境胁迫响应研究进展

角质层,包括角质和蜡质,是主要由脂肪酸及其衍生物构成的覆盖在植物的外表面的高度疏水层,在植物生长发育过程中起到非常重要的保护屏障作用。除了在极端温度、干旱、高盐等多种非生物逆境胁迫下起到保护作用外,还能够保护植物内部组织免受细菌、真菌病原体的侵染。现就植物角质层的组成、合成途径以及与植物抗逆性,特别是与抗旱能力的关系方面的最新研究进展进行了综述。     

Attenuated total reflectance spectroscopy of plant leaves: a tool for ecological and botanical studies

Attenuated total reflectance (ATR) spectra of plant leaves display complex absorption features related to organic constituents of leaf surfaces. The spectra can be recorded rapidly, both in the field and in the laboratory, without special sample preparation. This paper explores sources of ATR spectral variation in leaves, including compositional, positional and temporal variations. Interspecific variations are also examined, including the use of ATR spectra as a tool for species identification. Positional spectral variations generally reflected the abundance of cutin and the epicuticular wax thickness and composition. For example, leaves exposed to full sunlight commonly showed more prominent cutin- and wax-related absorption features compared with shaded leaves. Adaxial vs. abaxial leaf surfaces displayed spectral variations reflecting differences in trichome abundance and wax composition. Mature vs. young leaves showed changes in absorption band position and intensity related to cutin, polysaccharide, and possibly amorphous silica development on and near the leaf surfaces. Provided that similar samples are compared (e.g. adaxial surfaces of mature, sun-exposed leaves) same-species individuals display practically identical ATR spectra. Using spectral matching procedures to analyze an ATR database containing 117 individuals, including 32 different tree species, 83% of the individuals were correctly identified.     

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.