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A gradient of development consisting of successive zones of cell division, cell elongation and cell maturation occurs along the longitudinal axis of elongating leaf blades of tall fescue (Festuca arundinacea Schreb.), a C3 grass. An increase in specific leaf weight (SLW; dry weight per unit leaf area) in the maturation region has been hypothesized to result from deposition of secondary cell walls in structural tissues. Our objective was to measure the transverse cell wall area (CWA) associated with the increase in SLW, which occurs following the cessation of leaf blade elongation at about 25 mm distal to the ligule. Digital image analysis of transverse sections at 5, 15, 45, 75 and 105 mm distal to the ligule was used to determine cell number, cell area and protoplast area of structural tissues, namely fibre bundles, mestome sheaths and xylem vessel elements, along the developmental gradient. Cell diameter, protoplast diameter and area, and cell wall thickness and area of fibre bundle cells were calculated from these data. CWA of structural tissues increased in sections up to 75 mm distal to the ligule, confirming the role of cell wall deposition in the increase in SLW (r2 = 0.924; P < or = 0.01). However, protoplast diameter of fibre cells did not decrease significantly as CWA increased, although mean thickness of fibre cell walls increased by 95 % between 15 and 105 mm distal to the ligule. Therefore, secondary cell wall deposition in fibre bundles of tall fescue leaf blades resulted in continued radial expansion of fibre cells rather than in a decrease in protoplast diameter. 相似文献
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The pleiotropic effects of the Rld1-O/+ mutation of Zea mays (Poaceae) on leaf phenotype include a suppression of normal transverse unrolling, a reversed top/bottom epidermal polarity, and an apparently straighter longitudinal shape. According to engineering shell theory, there might be mechanical coupling between transverse and longitudinal habit, i.e., the leaf rolling itself might produce the longitudinal straightening. We tested this possibility with quantitative curvature measurements and mechanical uncoupling experiments. The contributions of elastic bending under self weight, mechanical coupling, and rest state of leaf parts to the longitudinal and transverse habit were assessed in Rld1-O/+ mutants and a population of sibling +/+ segregants. Elastic bending and curvature coupling are shown to be relatively unimportant. The Rld1-O/+ mutation is shown to alter not only the unrolling process, but also the developmental longitudinal curving in the growing leaf, leading to a straighter midrib and a rolled lamina. The Rld1-O/+ mutant is thus a suitable model to study the relation between tissue polarity and differential curvature development in the maize leaf. Since on the abaxial side of the leaf, more abundant sclerenchyma is found in +/+ than in Rld1-O/+, a gradient in sclerification may contribute to the development of midrib curvature. 相似文献
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Zhou Q Wang L Cai X Wang D Hua X Qu L Lin J Chen T 《Journal of plant physiology》2011,168(11):1249-1255
Casparian bands of endodermis and exodermis play crucial roles in blocking apoplastic movement of ions and water into the stele of roots through the cortex. These apoplastic barriers differ considerably in structure and function along the developing root. The present study assessed net Na+ fluxes in anatomically distinct root zones of rice seedlings and analyzed parts of individual roots showing different Na+ uptake. The results indicated that anatomically distinct root zones contributed differently to the overall uptake of Na+. The average Na+ uptake in root zones in which Casparian bands of the endo- and exo-dermis were interrupted by initiating lateral root primordia (root zone III) was significantly greater than that at the root apex, where Casparian bands were not yet formed (root zone I), or in the region where endo- and exo-dermis with Casparian bands were well developed (root zone II). The measurement of net Na+ fluxes using a non-invasive scanning ion-selective electrode technique (SIET) demonstrated that net Na+ flux varied significantly in different positions along developing rice roots, and a net Na+ influx was obvious at the base of young lateral root primordia. Since sodium fluxes changed significantly along developing roots of rice seedlings, we suggest that the significantly distinct net Na+ flux profile may be attributed to different apoplastic permeability due to lateral root primordia development for non-selective apoplastic bypass of ions along the apoplast. 相似文献
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蜈蚣草(Pteris vittata)是多年生的超积累砷植物,并用于修复受重金属污染的土壤。利用光学显微镜和荧光显微镜来研究蜈蚣草的解剖结构及组织化学特征,以此明确该物种适应干旱岩生环境,以及具有离子超富集作用的特点。结果表明(:1)蜈蚣草孢子体的根状茎、不定根和叶的结构均为初生结构,不定根的结构由内而外包括维管柱、内皮层、皮层、木质化厚壁组织层和表皮。(2)根状茎结构由内而外包括网状中柱、内皮层、皮层、表皮外覆盖的角质层。(3)羽状复叶的总叶柄的结构由内而外包括维管束、内皮层、皮层、厚壁组织层、表皮外覆盖的角质层。叶片为异面叶,表皮内方具厚壁层,叶表皮具角质层,仅下表皮有气孔。(4)蜈蚣草根表皮、皮层与根毛的表面富含果胶,皮层木质化;黄连素离子通透性试验结果显示,根毛、根表皮和皮层滞留大量黄连素离子。综上,植物体的内皮层、木质化厚壁组织层、异面叶和厚的角质层结构说明蜈蚣草适应岩生环境,根具木质化皮层和富含果胶的组织化学特点,以及离子通透性试验表明其与离子超积累功能有关。 相似文献
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Mervi M. Sepp?nen Kirsi Pakarinen Venla Jokela Jeppe R. Andersen Alice Fiil Arja Santanen Perttu Virkaj?rvi 《Annals of botany》2010,106(5):697-707
Background
Timothy is a long-day grass species well adapted for cultivation in northern latitudes. It produces elongating tillers not only in spring growth but also later in summer. As the quantity and quality of harvested biomass is dictated by canopy architecture and the proportion of stem-forming flowering tillers, the regulation of flowering is of great interest in forage grass production.Methods
Canopy architecture, stem morphology and freezing tolerance of vernalized timothy were investigated in greenhouse and field experiments. The molecular control of development was examined by analysing the relationship between apex development and expression of timothy homologues of the floral inducer VRN1 and repressor VRN2.Key Results
True stem formation and lignification of the sclerenchyma ring occur in both vernalized and regrowing stems irrespective of the developmental stage of the apex. The stems had, however, divergent morphology. Vernalization enhanced flowering, and the expression of the VRN1 homologue was elevated when the apex had passed into the reproductive stage. High VRN1 homologue expression was not associated with reduction in freezing tolerance and the expression coincided with increased levels of the floral repressor VRN2 homologue. Field experiments supported the observed linkage between the upregulation of the VRN1 homologue and the transition to the reproductive stage in vernalized tillers. The upregulation of putative VRN1 or VRN2 genes was restricted to vernalized tillers in the spring yield and, thus, not detected in non-vernalized tillers of the second yield; so-called regrowth.Conclusions
The formation of a lignified sclerenchyma ring that efficiently reduces the digestibility of the stem was not related to apex development but rather to a requirement for mechanical support. The observed good freezing tolerance of reproductive timothy tillers could be one important adaptation mechanism ensuring high yields in northern conditions. Both VRN1 and VRN2 homologues required a vernalization signal for expression so the development of yield-forming tillers in regrowth was regulated independently of the studied genes. 相似文献8.
Jiri Dolezal Adam Klimes Miroslav Dvorsky Pavel Riha Jitka Klimesova Fritz Schweingruber 《Oikos》2019,128(11):1576-1587
Understanding what determine plants ability to survive drought and cold is crucial for predicting how plants may respond to ongoing climate change. Plant survival strategies are usually characterized by morphological and physiological adaptations, while their underlying anatomical settings are largely unknown. Woody angiosperms and herbaceous dicots have repeatedly evolved small water transporting conduits and large storage parenchyma tissues at colder or drier places to cope with freezing‐ and drought‐induced damages. However, whether these adaptations are also valid for graminoids remains unclear. Here we show that stem anatomical variations in grasses, sedges and rushes dominating in western Himalayan grasslands are driven by elevation and soil moisture via control over aboveground plant stature and belowground clonal growth, while phylogenetic constraints have only a weak effect. Phylogenetic comparative analyses controlling for confounding factors showed that the elevation‐related cooling controls the conductive system through reduced vessel diameter and extended assimilatory and storage tissues with more chlorenchyma and less sclerenchyma around vessels. The soil moisture deficit, on the other hand, determines stabilization structures by promoting short‐rhizomatous turf graminoids with hollow stems, thicker epidermis and deep adventitious roots in dry steppes and semi‐deserts. Saline wetlands and moist alpine pastures promote long‐rhizomatous short‐stature plants with lower need for mechanical support (absence of hollow stem) and exposure to high evaporative forcing (thinner epidermis). Observed trends of decreasing vessel sizes and lignification rate with elevation supports the existing knowledge that narrower vessels and extensive parenchyma assist plants to grow in cold environments by avoiding freezing‐induced cavitation. Our results bring novel information on ecological drivers influencing the evolution of anatomical adaptations in high mountain graminoids. Distinct grassland types, covering elevations from 2650 to 6150 m, harbor unrelated species with different evolutionary histories that have converged towards similar anatomical structures. 相似文献
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Leaf anatomy and eco-physiology of Elymus repens, a temperate loess grassland species, were determined after seven years of exposure to 700 μmol (CO2) mol−1 (EC). EC treatment resulted in significant reduction of stomatal density on both surfaces of couch-grass leaves. Thickness
of leaves and that of the sclerenchyma tissues between the vessels and the adaxial surfaces, the area of vascular bundle,
and the volumes of phloem and tracheary increased at EC while abaxial epidermis and the sclerenchyma layer between the vessel
and the abaxial surface were thicker at ambient CO2 concentration (AC). Stomatal conductance and transpiration rates were lower in EC, while net CO2 assimilation rate considerably increased at EC exposure. Contents of soluble sugars and starch were higher in EC-treated
couch-grass leaves than in plants grown at AC.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献