青藏高原不同海拔高度下全缘叶绿绒蒿叶表皮特征研究

采用胶带粘取叶表皮法,利用光学显微镜观测不同海拔高度下全缘叶绿绒蒿叶片的表皮毛、气孔及表皮细胞结构特征,探讨全缘叶绿绒蒿叶表皮特征与海拔高度的关系。结果表明,随着海拔高度增加,全缘叶绿绒蒿叶片上、下表皮毛密度、气孔密度和表皮细胞密度逐渐增加;气孔器及表皮细胞的长度、宽度和面积逐渐减小;表皮细胞的形态随着海拔升高由无规则形向多边形变化,垂周壁由波状向弓形或平直变化。全缘叶绿绒蒿叶表皮结构在不同海拔高度下表现出的差异,可能是植物长期在高原生态环境下的综合反应,以结构上的变化来适应对高海拔地区的环境特点,为进一步研究高海拔地区植物的适应性提供一定依据。     

ULTRASTRUCTURE OF GLANDULAR TRICHOMES OF LEAVES OF NICOTIANA TABACUM L., cv XANTHI

Electron microscopy confirms previous light microscope observations that tobacco leaf trichomes are glandular and that there are two different types. Both the tall trichome (multicellular stalk, unicellular or multicellular head) and the short trichome (unicellular stalk; multicellular head) exhibit characteristics common to gland cells—a dense cytoplasm, numerous mitochondria, and little vacuolation. The tall trichome contains structurally well developed chloroplasts and an elaborate network of endoplasmic reticulum. The short trichome contains undifferentiated plastids and endoplasmic reticulum which parallels the nucleus and plasmalemma. Few dictyosomes are seen either in the short trichome or in the tall trichome. The short trichome appears to undergo structural changes concurrently with the appearance of secretory product within the cells. The most noticeable change is the formation of the extraplasmic space between the cell wall and the plasmalemma. Electron dense secretory product is observed between the plasmalemma and the cell wall and within the intercellular spaces.     

Cost of trichome production and resistance to a specialist insect herbivore in <Emphasis Type="Italic">Arabidopsis lyrata</Emphasis>

Theory predicts that trade-offs between resistance to herbivory and other traits positively affecting fitness can maintain genetic variation in resistance within plant populations. In the perennial herb Arabidopsis lyrata, trichome production is a resistance trait that exhibits both qualitative and quantitative variation. Using a paternal half-sib design, we conducted two greenhouse experiments to ask whether trichomes confer resistance to oviposition and leaf herbivory by the specialist moth Plutella xylostella, and to examine potential genetic constraints on evolution of increased resistance and trichome density. In addition, we examined whether trichome production is induced by insect herbivory. We found strong positive genetic and phenotypic correlations between leaf trichome density and resistance to leaf herbivory, demonstrating that the production of leaf trichomes increases resistance to leaf damage by P. xylostella. Also resistance to oviposition tended to increase with increasing leaf trichome density, but genetic and phenotypic correlations were not statistically significant. Trichome density and resistance to leaf herbivory were negatively correlated genetically with plant size in the absence of herbivores, but not in the presence of herbivores. There was no evidence of increased trichome production after leaf damage by P. xylostella. The results suggest that trichome production and resistance to leaf herbivory are associated with a cost and that the direction of selection on resistance and trichome density depends on the intensity of herbivory.     

Trichome layers versus dehaired lamina of Olea europaea leaves: differences in flavonoid distribution,UV-absorbing capacity,and wax yield

Leaf flavonoid compounds from six olive (Olea europaea L.) cultivars were analysed by HPLC. The composition of the soluble fractions of the dehaired lamina and the isolated trichome layers of the abaxial leaf surface were analysed in separate, as to study the distribution of flavonoids between the two leaf parts. Quercetin and quercetin 3-O-rhamnoside that have been reported to occur in the leaves seem to be located exclusively in the trichome layer. A greater variety of flavonoids was found in the lamina but the trichome layer was richer in terms of total flavonoids per unit mass. Trichome layer demonstrated an independent chemical character since its flavonoid concentration and composition was not coordinated with that of the lamina. The occurrence of flavonoid compounds in trichomes is related to the UV-filtering capacity of these cells. The results of the present study showed that apart from the soluble fraction, the cuticular waxes and cell walls of the trichomes also showed significant UV-absorbing capacity, indicating the occurrence of UV-absorbing compounds in these fractions as well. Moreover, the cuticular waxes of the trichome layer exhibited not only a higher investment of mass per unit of leaf area, but also a higher UV-absorbing capacity expressed per unit mass as compared to the cuticular waxes of the lamina surface. The importance for the separate chemical investigation of the phenolic composition of the leaf lamina and the trichome layers as well as the ecological significance of the findings is discussed.     

Cell-to-cell transport via the lumen of the endoplasmic reticulum

Plasmodesmata are plasma membrane‐lined channels through which cytoplasmic molecules move from cell‐to‐cell in plants. Most plasmodesmata contain a desmotubule, a central tube of endoplasmic reticulum (ER), that connects the ER of adjacent cells. Here we demonstrate that molecules of up to 10.4 kDa in size can move between the ER lumen of neighbouring leaf trichome or epidermal cells via the desmotubule lumen. Fluorescent molecules of up to 10 kDa, microinjected into the ER of Nicotiana trichome cells, consistently moved into the ER and nuclei of neighbouring trichome cells. This movement occurred more rapidly than movement via the cytoplasmic pathway. A fluorescent 3‐kDa dextran microinjected into the ER of a basal trichome cell moved into the ER and nuclei of epidermal cells across a barrier to cytoplasmic movement. We constructed a 10.4‐kDa recombinant ER‐lumenal reporter protein (LRP) from a fragment of the endogenous ER‐lumenal binding protein AtBIP1. Following transient expression of the LRP in the ER of Tradescantia leaf epidermal cells, it often moved into the nuclear envelopes of neighbouring cells. However, green fluorescent protein targeted to the ER lumen (ER‐GFP) did not move from cell to cell. We propose that the ER lumen of plant cells is continuous with that of their neighbours, and allows movement of small ER‐lumenal molecules between cells.     

Trichome cell growth in Arabidopsis thaliana can be derepressed by mutations in at least five genes

Leaf trichomes in Arabidopsis are unicellular epidermal hairs with a branched morphology. They undergo successive endoreduplication rounds early during cell morphogenesis. Mutations affecting trichome nuclear DNA content, such as triptychon or glabra3, alter trichome branching. We isolated new mutants with supernumerary trichome branches, which fall into three unlinked complementation groups: KAKTUS and the novel loci, POLYCHOME and RASTAFARI. They map to chromosomes IV, II, and V, respectively. The trichomes of these mutants presented an increased DNA content, although to a variable extent. The spindly-5 mutant, which displays a constitutive gibberellin response, also produces overbranched trichomes containing more nuclear DNA. We analyzed genetic interactions using double mutants and propose that two independent pathways, defined by SPINDLY and TRIPTYCHON, act to limit trichome growth. KAKTUS and POLYCHOME might have redundant actions mediating gibberellin control via SPINDLY. The overall leaf polysomaty was not notably affected by these mutations, suggesting that they affect the control of DNA synthesis in a tissue- or cell type-specific manner. Wild-type tetraploids also produce overbranched trichomes; they displayed a shifted polysomaty in trichomes and in the whole leaf, suggesting a developmental program controlling DNA increases via the counting of endoreduplication rounds.     

Exogenous Methyl Jasmonate Alters Trichome Density on Leaf Surfaces of Rhodes Grass (Chloris gayana Kunth)

Jasmonates, including jasmonic acid and its derivatives such as methyl jasmonate (MeJA), are plant growth substances that control various responses. Jasmonates regulate leaf trichome density in dicotyledonous plants, but their effects on the trichome density of monocotyledonous plants, such as those in the Poaceae, remain unclear. In the present study we examined the effects of exogenous MeJA on the trichome density of Rhodes grass, which has three kinds of trichomes: macrohairs, salt glands, and prickles. Exogenous MeJA significantly increased the densities of macrohairs and salt glands on the adaxial and abaxial leaf surfaces and those of prickles on the adaxial leaf surface. Because exogenous MeJA significantly reduced the leaf area, we calculated the number of trichomes per 1000 epidermal cells to eliminate the effects of reduced leaf area. Exogenous MeJA significantly increased the number of macrohairs per 1000 epidermal cells on both adaxial and abaxial leaf surfaces, but it significantly decreased the number of salt glands per 1000 epidermal cells on both surfaces. Exogenous MeJA had no significant effects on the number of prickles per 1000 epidermal cells on either of the leaf surfaces. These results indicate that exogenous MeJA alters the trichome density by affecting leaf area and trichome initiation, and the effects of exogenous MeJA on trichome initiation differ among the various trichome types.     

Defensive role of leaf trichomes in resistance to herbivorous insects in Datura stramonium

This study assessed the role of leaf trichome density as a component of resistance to herbivores, in six populations of Datura stramonium. Phenotypic selection on plant resistance was estimated for each population. A common garden experiment was carried out to determine if population differences in leaf trichome density are genetically based. Among population differences in leaf trichome density, relative resistance and fitness were found. Leaf trichome density was strongly positively correlated to resistance across populations. In 5 out of 6 populations, trichome density was related to resistance, and positive directional selection on resistance to herbivores was detected in three populations. Differences among populations in mean leaf trichome density in the common garden suggest genetic differentiation for this character in Datura stramonium. The results are considered in the light of the adaptive role of leaf trichomes as a component of defence to herbivores, and variable selection among populations.     

Leaf morphological and ultrastructural performance of eggplant (Solanum melongena L.) in response to water stress

The effects of water stress on leaf surface morphology (stomatal density, size, and trichome density of both adaxial and abaxial surfaces) and leaf ultrastructure (chloroplasts, mitochondria, and cell nuclei) of eggplant (Solanum melongena L.) were investigated in this study. Higher stomata and trichome densities were observed on abaxial surface compared with the adaxial surface. Compared with well watered (WW) plants, the stomata and trichome density of the abaxial surface increased by 20.39% and 26.23% under water-stress condition, respectively. The number of chloroplasts per cell profile was lesser, the chloroplasts became round in a shape with more damaged structure of membranes, the number of osmiophilic granules increased, and the number of starch grains decreased. The cristae in mitochondria were disintegrated. The cell nuclei were smaller and the agglomerated nucleoli were bigger than those of WW plants. Our results indicated that the morphological and anatomical responses enhanced the capability of plants to survive and grow during stress periods.     

Semi-automated 3D Leaf Reconstruction and Analysis of Trichome Patterning from Light Microscopic Images

Trichomes are leaf hairs that are formed by single cells on the leaf surface. They are known to be involved in pathogen resistance. Their patterning is considered to emerge from a field of initially equivalent cells through the action of a gene regulatory network involving trichome fate promoting and inhibiting factors. For a quantitative analysis of single and double mutants or the phenotypic variation of patterns in different ecotypes, it is imperative to statistically evaluate the pattern reliably on a large number of leaves. Here we present a method that enables the analysis of trichome patterns at early developmental leaf stages and the automatic analysis of various spatial parameters. We focus on the most challenging young leaf stages that require the analysis in three dimensions, as the leaves are typically not flat. Our software TrichEratops reconstructs 3D surface models from 2D stacks of conventional light-microscope pictures. It allows the GUI-based annotation of different stages of trichome development, which can be analyzed with respect to their spatial distribution to capture trichome patterning events. We show that 3D modeling removes biases of simpler 2D models and that novel trichome patterning features increase the sensitivity for inter-accession comparisons.     

γ-Radiation Induces Leaf Trichome Formation in Arabidopsis

We observed induction of additional trichome formation on the adaxial surface of mature leaves of Arabidopsis after massive doses (1-3 kilograys) of gamma-radiation from cobalt-60. A typical increase in trichome number was observed in the seventh leaf when the full expansion of the fifth leaf was irradiated. Under normal growth conditions, trichome numbers on the adaxial surface of seventh leaf of the Arabidopsis ecotypes Columbia (Col) and Landsberg erecta (Ler) were 122.5 +/- 22.7 and 57.5 +/- 14.5, respectively. However, gamma-radiation induced additional trichome formation and the numbers rose to 207.9 +/- 43.7 and 95.0 +/- 27.1 in Col and Ler, respectively. In Col the shape of new trichomes was intact and their formation was spatially maintained at equal distances from other trichomes. In Ler trichome morphology was aberrant and the formation was relatively random. Treatment with antioxidants before gamma-irradiation suppressed the increase in trichome number, and treatment with methyl viologen and light induced small trichomes. These results suggest that gamma-radiation-induced trichome formation is mediated by active oxygen species generated by water radiolysis. gamma-Radiation-induced trichome formation was blocked in the trichome mutants ttg-1, gl1-1, and gl2-1. These results suggest that gamma-radiation-induced trichome formation is mediated by the normal trichome developmental pathway.     

Cell-to-cell movement of potato virus X revealed by micro-injection of a viral vector tagged with the β-glucuronidase gene

The replication and cell-to-cell movement of potato virus X (PVX) has been studied using a PVX vector construct which expressed the β-glucuronidase (GUS) reporter gene in infected cells. Nicotiana clevelandii leaf trichome cells were micro-injected with the PVX-GUS vector and histochemical staining was used to locate GUS activity. The distribution of GUS activity revealed that PVX had moved from the injected cell into other trichome cells and into the cells along the leaf margin. GUS activity was always restricted to the cells at the edge of the leaf suggesting that PVX was unable to move out of the marginal cells. At the infection front, scattered along the leaf margin, there were isolated groups of cells staining for GUS activity. The absence of GUS activity in the intervening cells suggests that PVX had moved through several cells without replicating within them. This latter observation is consistent with previously reported observations that viral movement proteins are capable of moving between cells.     

Glandular trichomes as a barrier against atmospheric oxidative stress: Relationships with ozone uptake,leaf damage,and emission of LOX products across a diverse set of species

There is a spectacular variability in trichome types and densities and trichome metabolites across species, but the functional implications of this variability in protecting from atmospheric oxidative stresses remain poorly understood. The aim of this study was to evaluate the possible protective role of glandular and non‐glandular trichomes against ozone stress. We investigated the interspecific variation in types and density of trichomes and how these traits were associated with elevated ozone impacts on visible leaf damage, net assimilation rate, stomatal conductance, chlorophyll fluorescence, and emissions of lipoxygenase pathway products in 24 species with widely varying trichome characteristics and taxonomy. Both peltate and capitate glandular trichomes played a critical role in reducing leaf ozone uptake, but no impact of non‐glandular trichomes was observed. Across species, the visible ozone damage varied 10.1‐fold, reduction in net assimilation rate 3.3‐fold, and release of lipoxygenase compounds 14.4‐fold, and species with lower glandular trichome density were more sensitive to ozone stress and more vulnerable to ozone damage compared to species with high glandular trichome density. These results demonstrate that leaf surface glandular trichomes constitute a major factor in reducing ozone toxicity and function as a chemical barrier that neutralizes the ozone before it enters the leaf.     

Foliar trichomes, boundary layers, and gas exchange in 12 species of epiphytic Tillandsia (Bromeliaceae)

We examined the relationships between H2O and CO2 gas exchange parameters and leaf trichome cover in 12 species of Tillandsia that exhibit a wide range in trichome size and trichome cover. Previous investigations have hypothesized that trichomes function to enhance boundary layers around Tillandsioid leaves thereby buffering the evaporative demand of the atmosphere and retarding transpirational water loss. Data presented herein suggest that trichome-enhanced boundary layers have negligible effects on Tillandsia gas exchange, as indicated by the lack of statistically significant relationships in regression analyses of gas exchange parameters and trichome cover. We calculated trichome and leaf boundary layer components, and their associated effects on H2O and CO2 gas exchange. The results further indicate trichome-enhanced boundary layers do not significantly reduce transpirational water loss. We conclude that although the trichomes undoubtedly increase the thickness of the boundary layer, the increase due to Tillandsioid trichomes is inconsequential in terms of whole leaf boundary layers, and any associated reduction in transpirational water loss is also negligible within the whole plant gas exchange pathway.     

ABSORBING TRICHOMES IN THE PLEUROTHALLIDINAE (ORCHIDACEAE)

Glandular trichomes occur on both surfaces of leaves of all examined genera and species of the subtribe Pleurothallidinae (Orchidaceae). Trichome initiation is effected by one periclinal division of a protodermal cell, producing a thin-walled, globose apical cell with a relatively large nucleus and a subapical stalk cell with heavily cutinized lateral walls. In some species a second periclinal division produces a third small basal cell also having thick lateral walls but thin transverse walls. As leaf development proceeds, the trichome apparatus assumes a sunken position due to continued anticlinal divisions of protoderm. Prior to laminar expansion and guard-mother-cell division on the abaxial surface, the wall of the apical cell ruptures and is replaced by a brown opaque residue. Finally, after vascular tissue differentiation and the cessation of meristematic activity, two or more pitted foot cells develop at the base of the trichome and adjacent to the water-storing hypodermal layers. Preliminary investigations indicate that the trichome apparatus is absorptive throughout its development and similar in function to tillandsioid scales in Bromeliaceae.