植物不同类型表皮毛调控模型研究进展

表皮毛是植物地上部分表皮细胞向外突出延伸的特化毛状结构,不仅可以保护植物免受病虫的危害,还具有一定的经济和药用价值,对其调控的分子机制的阐明有利于植物的分子设计育种和遗传改良。近年来,模式植物拟南芥表皮毛形成的调控模式基本被阐明,其他植物表皮毛的调控机制也取得很大进展。鉴于此,文中综述了拟南芥和棉花(单细胞表皮毛)及番茄和青蒿(多细胞表皮毛)在基因和激素水平上对表皮毛的发育调控,同时简要介绍了其他典型单、双子叶植物表皮毛相关的研究进展,最后,展望了植物表皮毛的研究方向和应用前景。     

珍稀濒危植物翅果油树表皮毛的微形态观察研究

利用体视显微镜、扫描电镜和光学显微镜,对珍稀濒危植物翅果油树(Elaeagnus mollis Diels)的茎、叶、果、休眠芽等多种器官表面覆盖的表皮毛,进行了详细观察．发现其表皮毛的形态和结构具有多样性,各器官有差异,据此将它们分为分支状毛、星状毛、盾状-星状毛、盾状毛四类,以及一些特殊的表皮毛,如：分支状毛与星状毛或盾状-星状毛的过渡类型称为类星状毛和类盾状-星状毛．叶片上表面的表皮毛,为分枝状表皮毛,且稀疏散布．叶片下表面的白色表皮毛,也多为分枝状表皮毛,但分布较密,叶主脉处最为稠密多为星状毛．叶柄的表皮毛形态呈现一定的梯度变化,远轴端(靠近叶片端)为类星状毛,近轴端(靠近茎的一端)为盾状-星状表皮毛,中间段为星状毛介于前二者之间．茎表面灰色的或褐色的表皮毛,以盾状表皮毛为主,夹杂少量盾状-星状表皮毛,因茎的老嫩其表皮毛形态略有不同．外果皮沟槽内的表皮毛多为盾状表皮毛,嵴部则密集星状或分支状表皮毛．休眠芽的鳞片多覆盖盾状表皮毛,只在鳞片的尖端有少量星状毛和分枝状毛．翅果油树多种器官表面多种表皮毛的存在是其适应高山(海拔800～1300m)环境的一种形态特征．表皮毛具有反射阳光、阻止水分过度散失、保温、防止机械损伤等功能．为探究翅果油树耐早、耐寒、耐高温机理以及组织培养过程中外植体易污染等问题,提供了形态学依据,也为进一步进行表皮毛的发育和分子生物学研究打下了一定的基础。     

翅果油树叶表皮毛发育的研究

利用扫描电镜和光学显微镜,对国家二级保护植物翅果油树(Elaeagnus mollis Diels)叶表皮毛的结构及发育,进行了详细的观察。翅果油树叶表皮毛有两种类型：分枝状表皮毛和盾状表皮毛,两者都是由头部和柄部组成。两类表皮毛的原始细胞均起源于叶原基或幼叶的原表皮细胞,经过两次垂周分裂形成四细胞。在发育后期,四细胞的分化状态决定表皮毛的类型。若四细胞平周分裂成上下八细胞,将发育成分枝状表皮毛的头部;若继续垂周分裂成同层八细胞,将发育成盾状表皮毛的头部。柄部的发育过程基本相同,都是由紧靠头部的表皮细胞和叶肉细胞发育而来。     

旱生植物叶上密生的表皮毛的功能

很多旱生植物叶的上下表皮上分布着浓密的表皮毛。长期以来人们认为它们可以阻碍叶表面空气的流动,因此,具有减少水分从气孔蒸发的功能。但有些试验(Johnson,1975)却证明了某些具有密生表皮毛的植物,其水分的蒸发量反而更高些。因为水分是可以通过表皮毛细胞的细胞壁扩散出去的(质体外扩散途径,apoplastic route)。水分通过具有很大蒸发表面的表皮毛细胞壁的蒸发量,可能会多于因气孔被遮蔽所减少的水分蒸发量,所以某些具有密生表皮毛的植物可能会有较高的水分蒸发量。 Fahn(1986)观察了12种旱生植物叶的表皮毛,发现这些表皮毛基部细胞的壁都是经过了角质化的,水分是不可能通过这些角质化了的细胞壁扩散出去的。所以     

旱生植物叶密生的表皮毛具有阻止水分蒸发的功能吗?

很多早生植物叶的上下表皮上分布着密生的表皮毛,使在其下面的气孔被遮盖着。所以长时期以来人们认为这种密生的表皮毛有阻碍叶表面空气的流通和阻止水分从气孔蒸发的功能。但是有些试验却证明某些生有密生表皮毛的植物的水分蒸发量反而比具有较少表皮毛的更高些(Johnson HB.BotRev1975,41:222),刚好与人们的习惯看法相反。实际上,水分可以通过质外(apoplast)或共质(symplast)的扩散途径从密生的表皮毛扩散出去。蒸发表面很大的表皮毛所蒸发的水分量可能会比由于气孔的被遮盖所减少的水分蒸发量要大,因此某些生有密生表     

拟南芥表皮毛发育的分子机制

拟南芥（Arabidopsis thaliana）表皮毛是存在于地上部分表皮组织的一种特化的、典型的单细胞结构。近几年,对其发育的分子调控机制的研究取得了很大进展,已克隆出大量的控制表皮毛不同发育阶段的基因,通过对这些基因的功能解析揭示出表皮毛发育及生长调节的内在分子机制。该文对拟南芥表皮毛发育的最新研究进展进行综述,并展望了关于表皮毛的研究方向及潜在的应用价值。     

拟南芥表皮毛发育的分子机制

拟南芥(Arabidopsis thaliana)表皮毛是存在于地上部分表皮组织的一种特化的、典型的单细胞结构。近几年, 对其发育的分子调控机制的研究取得了很大进展, 已克隆出大量的控制表皮毛不同发育阶段的基因, 通过对这些基因的功能解析揭示出表皮毛发育及生长调节的内在分子机制。该文对拟南芥表皮毛发育的最新研究进展进行综述, 并展望了关于表皮毛的研究方向及潜在的应用价值。     

中国产委陵菜属叶表皮毛的研究

在光学显微镜和实体解剖镜下对28种和变种国产委陵菜属植物的叶表皮毛进行了研究,结果如下：1．在所观察的植物中,有4种类型叶表皮毛的存在,即：单细胞直的不分支的毛;单细胞卷曲的不分支的毛;腺毛;星状毛。2．叶表皮毛的种类在本属植物中具有稳定性,因此具有一定的分类学价值。3．腺毛在所观察的植物中普遍存在。4．讨论了金露梅、银露梅、小叶金露梅的系统归属。     

亚洲粗叶木属及相关属植物叶表皮微形态特征

利用光学显微镜和电子扫描显微镜研究了亚洲茜草科粗叶木属植物26种（包括1个亚种和2个变种）和相关4属即巴戟天属、九节属、染木属和尖叶木属6种植物的叶表皮微形态特征。粗叶木属植物上表皮细胞形状一般呈不规则波状、近椭圆形或者不规则多边形,下表皮细胞一般呈不规则皱波状或者多裂深波状,细胞壁曲折无章,细胞间界限不明显,上、下表皮细胞壁均有加厚现象。叶表皮角质层明显,在电镜下有以下几种类型：颗粒状,网状,鳞片状,乳突状。气孔器几乎全部生在下表皮,有些种气孔下陷,气孔器一般是一对保卫细胞和一对副卫细胞平列。一些粗叶木属植物种叶上着生表皮毛。表皮毛分为单细胞毛和单列多细胞毛两种结构类型以及扭曲毛,线形毛和直壁毛3种形态类型。相关属的叶表皮微形态特征与粗叶木属植物较为相似。粗叶木属植物叶表皮微形态特征具有一定的分类学价值,其性状虽有遗传稳定性,但随生态环境不同而有一定变异。粗叶木属植物叶气孔长轴径/径轴变化幅度比较大以及叶表皮上的毛被多样化均能反映其对生态环境的适应变化。     

贺兰山15种旱生灌木叶表皮扫描电镜观察

对15种天然分布在宁夏贺兰山荒漠地区的旱生灌木叶表皮进行扫描电镜观察发现,这些植物叶的上、下表皮细胞角质膜加厚,且分布有大量的表皮毛,有单细胞毛和多细胞毛;气孔器被表皮毛覆盖,均为内陷气孔。这些形态结构是植物适应干旱环境的典型特征。     

Trichome morphogenesis in Arabidopsis

Trichomes (plant hairs) in Arabidopsis thaliana are large non-secreting epidermal cells with a characteristic three-dimensional architecture. Because trichomes are easily accessible to a combination of genetic, cell biological and molecular methods they have become an ideal model system to study various aspects of plant cell morphogenesis. In this review we will summarize recent progress in the understanding of trichome morphogenesis.     

Characterization and density of trichomes on three common bean cultivars

Trichomes have been implicated as a mechanism which can confer resistance to both plant pests and drought. A study was conducted to provide information regarding genetic variability for trichome distribution and density among three diverse dry bean (Phaseolus vulgaris L.) cultivars, and to characterize the types of trichomes present among the cultivars. Trichomes on the leaf surfaces were micrographed with a scanning electron microscope (SEM) and counted using a stereomicroscope on both the abaxial and adaxial leaf surfaces of the cultivars ‘Bill Z’, ‘Pompadour Checa’ and ‘Diacol Calima’. Straight, hooked, and glandular trichomes were observed on the leaf surfaces of each cultivar. SEM micrographs are presented for the leaf surfaces of each cultivar and trichome type. The abaxial leaf surface had more straight trichomes than the adaxial leaf surface for ‘Pompadour Checa’ and ‘Diacol Calima’, however ‘Bill Z’ had more on the adaxial surface. The opposite relationship existed among the cultivars and leaf surfaces for the hooked trichomes.     

Incidence of the introduced parasitoids Cotesia kazak and Microplitis croceipes (Hymenoptera: Braconidae) from Helicoverpa armigera (Lepidoptera: Noctuidae) in tomatoes, sweet corn, and lucerne in New Zealand

Morphological defense traits of plants such as trichomes potentially compromise biological control in agroecosystems because they may hinder predation by natural enemies. To investigate whether plant trichomes hinder red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), as biological control agents in soybean, field and greenhouse experiments were conducted in which we manipulated fire ant density in plots of three soybean isolines varying in trichome density. Resulting treatment effects on the abundance of herbivores, other natural enemies, plant herbivory, and yield were assessed. Trichomes did not inhibit fire ants from foraging on plants in the field or in the greenhouse, and fire ant predation of herbivores in the field was actually greater on pubescent plants relative to glabrous plants. Consequently, fire ants more strongly reduced plant damage by herbivores on pubescent plants. This effect, however, did not translate into greater yield from pubescent plants at high fire ant densities. Intraguild predation by fire ants, in contrast, was weak, inconsistent, and did not vary with trichome density. Rather than hindering fire ant predation, therefore, soybean trichomes instead increased fire ant predation of herbivores resulting in enhanced tritrophic effects of fire ants on pubescent plants. This effect was likely the result of a functional response by fire ants to the greater abundance of caterpillar prey on pubescent plants. Given the ubiquity of lepidopteran herbivores and the functional response to prey shown by many generalist arthropod predators, a positive indirect effect of trichomes on predation by natural enemies might be more far more common than is currently appreciated.     

Transgenerational effects alter plant defence and resistance in nature

Trichomes, or leaf hairs, are epidermal extensions that take a variety of forms and perform many functions in plants, including herbivore defence. In this study, I document genetically determined variation, within‐generation plasticity, and a direct role of trichomes in herbivore defence for Mimulus guttatus. After establishing the relationship between trichomes and herbivory, I test for transgenerational effects of wounding on trichome density and herbivore resistance. Patterns of interannual variation in herbivore density and the high cost of plant defence makes plant–herbivore interactions a system in which transgenerational phenotypic plasticity (TPP) is apt to evolve. Here, I demonstrate that parental damage alters offspring trichome density and herbivore resistance in nature. Moreover, this response varies between populations. This is among the first studies to demonstrate that TPP contributes to variation in nature, and also suggests that selection can modify TPP in response to local conditions.     

Herbivore handling of a Plants trichome: the case of Heliconius charithonia (L.) (Lepidoptera: Nymphalidae) and Passiflora lobata (Killip) Hutch. (Passifloraceae)

Trichomes reduce herbivore attack on plants by physically and/or chemically inhibiting movement or other activities. Despite evidence that herbivores are negatively affected by trichomes there also reports of insect counter-adaptations that circumvent the plants defense. This paper reports on a study that investigated the likely mechanisms employed by larvae of the nymphalid butterfly, Heliconius charithonia (L.), that allow it to feed on a host that is presumably protected by hooked trichomes (Passiflora lobata (Killip) Hutch). Evidence were gathered using data from direct observations of larval movement and behavior, faeces analysis, scanning electron microscopy of plant surface and experimental analysis of larval movement on plants with and without trichomes (manually removed). The latter involved a comparison with a non specialist congener, Heliconius pachinus Salvin. Observations showed that H. charithonia larvae are capable of freeing themselves from entrapment on trichome tips by physical force. Moreover, wandering larvae lay silk mats on the trichomes and remove their tips by biting. In fact, trichome tips were found in the faeces. Experimental removal of trichomes aided in the movement of the non specialist but had no noticeable effect on the specialist larvae. These results support the suggestion that trichomes are capable of deterring a non specialist herbivore (H. pachinus). The precise mechanisms that allow the success of H. charithonia are not known, but I suggest that a blend of behavioral as well as physical resistance mechanisms is involved. Future studies should ascertain whether larval integument provides physical resistance to trichomes.     

Progress on trichome development regulated by phytohormone signaling

Trichomes are specialized structures that develop from epidermal cells in the aerial parts of plants, and are an excellent model system to study all aspects of cell differentiation including cell fate determination, cell cycle regulation, cell polarity and cell expansion. The development of the trichome is a process of integration of both external signals and endogenous developmental programs. During recent years, molecular analysis of trichome development at different stages has been well studied, and through the mutant phenotypes and the function of corresponding genes, the underlying mechanism has been revealed in a first glimpse. This paper offers a mini-view on this integration process with emphasis on the effects of plant hormone signaling on trichome development in plants through GLABROUS INFLORESCENCE STEMS (GIS) family and subfamily genes.     

Characteristic Trichomes and Indumentum Specialization in African and European Parasitic Scrophulariaceae

Trichomes and their distribution patterns have been observed in the aerial parts of plants of the genera Striga, Buchnera, Rhamphicarpa, Euphrasia, Melampyrum and Rhinanthus, using both light (LM) and scanning electron microscopy (SEM). All trichomes belong to the multicellular, uniseriate category and can be classified as glandular and nonglandular types. On nearly all organs, the two types can be observed side by side. Apart from a large group of ubiquitous trichomes, some characteristic trichome types are reported; they are restricted either to chlorophyllous organs (foliage leaves, bracts, calyx and stem) or to the corolla. In some nonglandular trichomes mineral deposits have been found. Other morphological and anatomical trichome features are discussed with regard to their possible function.