植物脱水素的结构和功能

脱水素（DHN）属于LEA蛋白（late embrygenesis abundant protein）第二家族成员,具有广泛的生物学功能,如防止细胞脱水,稳定细胞膜,结合金属离子,清除羟基自由基防止膜脂过氧化,保护冷敏感性酶活性,作为分子伴侣和结合DNA／RNA的特性等。本文介绍脱水素的结构,在植物器官、组织和亚细胞中的定位以及功能的研究进展。     

Accumulation of Dehydrins and ABA-Inducible Proteins in Wheat Seedlings during Low-Temperature Acclimation

Using one-dimensional SDS-PAGE and immunochemical methods, we detected the presence and estimated the content of dehydrins and ABA-inducible (RAB) polypeptides in etiolated seedlings of four spring and three winter wheat (Triticum aestivum L.) cultivars differing in frost hardiness. We hardened three-day-old seedlings at 4°C for nine days or grew them at 22°C for a day (control seedlings). We established that heat-stable cold-regulated (COR) polypeptides with mol wts of 209, 196, 169, 66, 50, and 41 kD, which are characteristic of hardened wheat seedlings, were homologous to polypeptides from a dehydrin family and polypeptides with mol wts of 209, 196, 66, 50, and 41 kD were immunologically related to RAB-proteins. We supposed that these COR polypeptides were involved in the prevention of local protein dehydration and denaturation during hypothermia. Analysis of the relative content of COR proteins revealed a close correlation between the cultivar frost hardiness and the concentration of these proteins. It seems evident that different accumulation of dehydrins and RAB polypeptides in different cultivars of a single species is one of the causes for different plant frost hardiness.     

Seasonal Changes in the Composition and Content of Dehydrins in Winter Wheat Plants

Seasonal changes in the pattern and content of dehydrins in winter wheat (Triticum aestivum) plants grown under field and laboratory conditions were studied by one-dimensional PAGE and immunochemical methods. During hardening, plants accumulated dehydrin-like polypeptides with mol wts of 209, 196, 66, 50, and 41 kD. In winter, low-molecular-weight dehydrins with mol wts of 24, 22, 17, 15, and 12 kD were synthesized and accumulated as well. Their content dropped sharply in spring when plants became unhardened. Accumulation/disappearance of these proteins corresponded to the fluctuations in wintering plant frost tolerance before winter and in spring. It is assumed that both high- and medium-molecular-weight dehydrins are involved in plant stress responses and adaptation, whereas low-molecular-weight dehydrins are evidently involved only in the process of low-temperature adaptation.     

脱水素研究进展

脱水素(dehydrin)是植物体内的一种LEA蛋白,能够在植物胚胎发育后期以及逆境下大量表达,广泛存在于植物界。它是具有高度热稳定性的亲水性蛋白,有三类非常保守的区域,即K,Y和S片段。依据这三类片段的组成情况,可将脱水素分为5个基本类别。脱水素可通过多种转运方式定位于植物细胞的不同部位,以行使其功能。其基因的表达存在依赖ABA和不依赖ABA两种途径,并且受到多种环境因素的影响,能稳定细胞膜和许多大分子的结构以避免脱水对细胞造成的伤害。近年来,脱水素的结构和组成、在细胞中的定位及转运、基因的表达与调控、功能与作用机理等方面的研究已取得了很大的进展。     

Photoperiodic induction of dormancy and freezing tolerance in Betula pubescens. Involvement of ABA and dehydrins

In many woody plants photoperiod signals the initiation of dormancy and cold acclimation. The photoperiod-specific physiological and molecular mechanisms have remained uncharacterised. The role of abscisic acid (ABA) and dehydrins in photope-riod-induced dormancy and freezing tolerance was investigated in birch, Betula pubescens Ehrh. The experiments were designed to investigate if development of dormancy and freezing tolerance under long-day (LD) and short-day (SD) conditions could be affected by manipulation of the endogenous ABA content, and if accumulation of dehydrin-like proteins was correlated with SD and/or the water content of the buds. Experimentally, the internal ABA content was increased by ABA application and by water stress treatment under LD, and decreased by blocking the synthesis of ABA with fluridone under SD. Additionally, high humidity (95% RH) was applied to establish if accidental water stress was involved in SD. ABA content was monitored by gas chromatography-mass spectrometry with selective ion monitoring (SIM). Short days induced a transient increase in ABA content, which was absent in 95% RH, whereas fluridone treatment decreased ABA. Short days induced a typical pattern of bud desiccation and growth cessation regardless of the treatment, and improved freezing tolerance except in the fluridone treatment. ABA content of the buds was significantly increased after spraying ABA on leaves and after water stress, treatments that did not induce cessation of growth and dormancy, but improved freezing tolerance. In addition to several constitutively produced dehydrins, two SD-specific proteins of molecular masses 34 and 36 kDa were found. Photoperiod- and experimentally-induced alterations in ABA contents affected freezing tolerance but not cessation of growth and dormancy. Therefore, involvement of ABA in the photoperiodic control of cold acclimation is more direct than in growth cessation and dormancy. As the typical desiccation pattern of the buds was found in all SD plants, and was not directly related to ABA content or to freezing tolerance, this pattern characterises the onset of photo-period-induced growth cessation and dormancy. The results provide evidence for the existence of various constitutively and two photoperiod-induced dehydrins in buds of birch, and reveal characteristics of dormancy and freezing tolerance that may facilitate further investigations of photoperiodic control of growth in trees.     

植物激素ABA在水分胁迫下的功能及信号途径

植物根系感知外界水分胁迫刺激,诱导ABA生物合成。ABA既可诱导气孔关闭或抑制气孔开放,以降低植物的蒸腾失水,又可影响植物根系发育,以抵御水分胁迫。本文就植物激素ABA及其下游信号H2O2、NO以及Ca2＋等在植物生长调节方面的研究进展进行概述,以构建水分胁迫下植物生长自我调控的可能模式。     

Improvement of the maturation and germination of horse chestnut somatic embryos

Embryogenic tissues obtained from stamen filament cultures of horse chestnut (Aesculum hippocastanum L.) were cultured on maturation media supplemented with different combinations of abscisic acid, polyethylene glycol 4000, mannitol or activated charcoal. Somatic embryos were subjected to different desiccation procedures after a culture period on maturation media. After a slow desiccation, obtained by placing the somatic embryos in empty and non-sealed Petri dishes under the laminar air flow for 48 h, an increase in viability, shoot elongation and conversion was observed for the embryos previously cultured on medium enriched with ABA (80 M) alone or plus PEG (50 g l^–1).     

Common amino acid sequence domains among the LEA proteins of higher plants

LEA proteins are late embryogenesis abundant in the seeds of many higher plants and are probably universal in occurrence in plant seeds. LEA mRNAs and proteins can be induced to appear at other stages in the plant's life by desiccation stress and/or treatment with the plant hormone abscisic acid (ABA). A role in protecting plant structures during water loss is likely for these proteins, with ABA functioning in the stress transduction process. Presented here are conserved tracts of amino acid sequence among LEA proteins from several species that may represent domains functionally important in desiccation protection. Curiously, an 11 amino acid sequence motif is found tandemly repeated in a group of LEA proteins of vastly different sizes. Analysis of this motif suggests that it exists as an amphiphilic helix which may serve as the basis for higher order structure.     

Structure and Function of the Plant Alternative Oxidase: Its Putative Role in the Oxygen Defence Mechanism

Current understanding of the structure and function of the plant alternative oxidase is reviewed. In particular, the role of the oxidase in the protection of tissues against oxidative stress is developed.     

高等植物中蛋白磷酸酶2C的结构与功能

蛋白质磷酸化／去磷酸化是生物信号级联传递的重要方式之一,主要通过生化性质互为对立的蛋白激酶和蛋白磷酸酶实现。蛋白磷酸酶2C(PP2C)是蛋白磷酸酶的一个分支,其生化性质、蛋白质组成与结构都和其他磷酸酶显著不同,但都在生物信号传递中扮演重要角色。高等植物中PP2C广泛参与脱落酸(ABA)的各种信号途径,包括ABA诱导的种子萌发／休眠、保卫细胞及离子通道调控和气孔关闭、逆境胁迫等。PP2C也多样地参与植物创伤反应、生长发育以及抗病性等各个途径。作为大多数信号途径的负调控因子,PP2C能直接与激酶结合,与其他调控蛋白结合,以及直接与DNA结合调控相关基因的表达。     

The effect of abscisic acid on chlorophyll fluorescence in lichens under extreme water regimes

Chlorophyll fluorescence measurements were used to test whether externally applied abscisic acid (ABA) has an effect on the desiccation tolerance of lichens and their sensitivity to constant water saturation. A surplus of ABA did not decrease the time required to regain full photosynthetic capacity after prolonged dry periods. However, an effect of ABA could be observed when lichens were permanently hydrated at moderately high temperatures. Lichens suffered less from constant saturation if ABA was added to the incubation medium. These results suggest a positive effect of ABA on membrane function.     

The egg-shell of Labiostrongylus eugenii (nematoda,strongyloidea): Structure and function

The egg-shell of Labio-strongylus eugenii consists of three layers; an outer vitelline layer, a middle chitinous layer and an inner lipid layer. The presence of chitin and protein in the middle layer was demonstrated by the use of chitinase and differential staining. The lipid layer was found to be made up of two layers, the innermost having large globules on its outer face. The shell was found to be permeable to liquid water, as demonstrated by the penetration of vital dyes. Eggs were able to develop normally with little or no loss of volume during periods of moisture stress when either osmotic or suction pressures were applied. The survival of eggs, as measured by hatching success, over periods of time at a range of saturation deficits and osmotic pressures was measured, and compared with known survival rates for other nematode species. The problems of working with nematode species whose life cycles have not been established are discussed. Possible survival strategies for Australian strongylids during periods of moisture stress are outlined.     

植物内源ABA水平的动态调控机制

ABA具有调节植物生长发育和对环境胁迫做出快速反应的重要功能, 植物内源ABA水平受到ABA合成、代谢及转运等途径的复杂调控。该文综述了近年来植物ABA从头合成、羟基化代谢、可逆糖基化代谢及ABA转运等领域的最新研究进展, 重点讨论ABA合成与代谢基因的表达调控机制, 并展望了今后的研究方向。