Proline Accumulation during Water Stress in Resurrection Plants

In leaves of resurrection plants dried intact, free prolineincreased in nine species and remained unchanged or declinedin two other tolerant species. Infiltration of proline into hydrated resurrection leaves oftwo species (a relatively high accumulator of proline, Borya,and low accumulator, Myrothamnus) prior to dehydration did notimprove the cells' survival rate, and in some cases caused adecrease in survival. These data indicate that the extreme drought tolerance of resurrectionplants is not related per se to proline levels.     

植物复苏性状的分子机理研究进展

复苏性状是某些生物应对水分剧烈变化恶劣环境的一种特殊适应能力,在植物界广泛分布于苔藓和蕨类低等植物,一些高等植物也具有这种性状。复苏植物可以在损失体内95％以上的水分后,遇水而复苏,以此度过环境恶劣的时段。复苏性状的分子机制一直让人们着迷,但对其认知还十分有限。近年来的研究表明,一些小分子代谢物和特殊蛋白的大量积累在复苏植物脱水过程中对生物膜和大分子结构起保护作用;复苏性状中的信号转导与基因调控可能包括ABA在内的一系列信号分子和途径。随着“组学”技术的发展,更宽广角度的研究将会极大的促进人们对复苏性状的认知。对于复苏性状的深入研究,可能为农作物和蔬菜的改良提供一个全新的方向,具有很大的潜在应用价值。     

Resurrection Plants: The Puzzle of Surviving Extreme Vegetative Desiccation

Tolerance to near complete desiccation of vegetative organs is a widespread capability in bryophytes and is also shared by a small group of vascular plants known as resurrection plants. To date more than 300 species, belonging to pteridophytes and angiosperms, have been identified that possess this kind of desiccation-tolerance. The vegetative desiccation-tolerance of resurrection plants is an inductive process displayed only under environmental stress with or without the involvement of abscisic acid as molecular signal. The different problems associated with desiccation encountered by resurrection plants render the employment of many interacting mechanisms necessary. Preservation of cell order and correct structure of membranes and macromolecules is underpinned by the synthesis of large amounts of sugars, amino acids, and small polypeptides such as late embryogenesis abundant (LEA) proteins and dehydrins. Some of these compatible solutes, such as sucrose and LEA proteins, are also involved in cytoplasm vitrification, which occurs during the last phase of desiccation. Mechanical damage due to vacuole shrinkage in dehydrating cells is avoided by cell wall folding or by replacing the water in vacuoles with nonaqueous substances. Oxidative stress, due to enhanced production of reactive oxygen species (ROS) especially by chloroplasts, is minimized through two different strategies. The homoiochlorophyllous resurrection plants, which conserve chloroplasts with chlorophylls and thylakoids upon drying, fold leaf blades and synthesize anthocyanins, as both sunscreens and free radical scavengers, and additionally increase the activity of antioxidant systems in cells. In contrast, the chloroplasts in poikilochlorophyllous species degrade chlorophylls and thylakoid membranes yielding desiccoplasts that are devoid of any internal structures. These adaptive mechanisms preserve cells from damage by desiccation and allow them to resume vital functions once rehydrated. Even if based mainly on cell protection during drying, the vegetative desiccation-tolerance of resurrection plants also relies on systems of cell recovery and repair upon rehydration. However, most of these systems are prepared during cell dehydration.     

Sulphydryl and Disulphide Levels in Protein Fractions from Hydrated and Dry Leaves of Resurrection Plants

Significant changes in sulphydryl (‘SH’) and disulphide(‘SS’) levels during air-drying in leaves of ‘resurrection’plants (whose protoplasm survives dehydration) stemmed mainlyfrom protein turnover effects. No significant changes were foundin the SH, SS levels in leaves of the desiccation sensitivespecies Sporobolus pyramidalis following air-drying. The three tolerant species studied differed in the directionof change. Some data were consistent with Levitt's SH, SS hypothesis:increases in protein-SS levels in Sporobolus stapfianus (desiccationtolerant) were consistent with a stabilization of new proteinby SS bonds; lower reactivity of protein-SH in the tolerantspecies Talbotia elegans (which on the other hand has decreasedprotein-SS) is consistent with a second mechanism of decreasingprotein denaturation proposed in Levitt's hypothesis. Evidence of some conversion of SH to SS in the soluble proteinsof Xerophyta viscosa (a tolerant species) would on Levitt'shypothesis indicate an injurious process. Some degree of proteindenaturation might be indicated by partial inactivation of thesoluble enzyme ribulose bisphosphate carboxylase in this species,and loss of some soluble isoenzymes (peroxidase and alkalinephosphatase). An apparent lack of SH conversion to SS in thesensitive species Sporobolus pyramidalis was not consistentwith the SH, SS hypothesis. Resurrection plants, Sporobolus pyramidalis, Sporobolus stapfianus, Talbotia elegans, Xerophyta viscosa, drought resistance, desiccation tolerance, protein turnover, sulphydryl groups     

彩叶植物叶片呈色分子机制研究进展

彩叶植物叶片呈现不同的颜色主要是受遗传因素和外部环境的共同作用,揭示彩叶植物叶片呈色机制对选育彩叶植物新品种和彩叶植物的应用推广具有重要理论和实践意义。目前对彩叶植物呈色机制的研究主要集中于叶片中色素变化、光合特性、叶片结构和环境条件等方面。该文主要対近年来有关彩叶植物叶片中叶绿素代谢途径、类胡萝卜素代谢途径、次生代谢途径、光合作用和叶绿体发育相关结构基因和转录因子调控机制的研究进展进行综述,并对以后的研究方向进行了展望,为培育彩叶植物新品种提供了理论基础,也为人工调控叶色以及叶色的定向遗传改良提供了参考。     

Dessication-induced Changes in the Protein Complement of Soluble Extracts from Leaves of Resurrection Plants and Related Desiccation-sensitive Species

Polyacrylamide gel electrophoresis studies were conducted onthe soluble proteins of angiosperm plants whose leaf protoplasmcan revive from complete dehydration (Xerophyta viscosa, Talbotiaelegans, Sporobolus stapfianus, Myrothamnus flabellifolia, Boryanitida) and of desiccation sensitive plants (Sporobolus pyramidalis,Eragrostis tenuifolia, Selaginella kraussiana). Changes in thesoluble protein composition were found in all species afterdehydration, and were extensive in most species, both resurrectionand non-resurrection. Both groups showed loss of protein bands,but there was no consistent pattern of compositional changewithin either type of plant. Net hydrolysis of high molecularweight protein could be deduced, and the possibility of disulphide-mediatedaggregation arose in some species. Induction of tolerance todesiccation in Borya nitida appeared to be associated with retentionor restoration of the control pattern of protein bands in contrastto loss of very low and very high mol. wt protein (loss wasextreme in desiccation-killed leaves). There was evidence of a disproportionately great synthesis ofvery low mol. wt protein during the midphase of rehydrationin X. viscosa. These results point to the possibility of an important roleof protein synthesis for survival of dehydration. Resurrection plants, desiccation-sensitive plants, protein complement, polyacrylamide gel electrophoresis     

A Survey of Plants for Leaf Peroxisomes

Leaves of 10 plant species, 7 with photorespiration (spinach, sunflower, tobacco, pea, wheat, bean, and Swiss chard) and 3 without photorespiration (corn, sugarcane, and pigweed), were surveyed for peroxisomes. The distribution pattern for glycolate oxidase, glyoxylate reductase, catalase, and part of the malate dehydrogenase indicated that these enzymes exist together in this organelle. The peroxisomes were isolated at the interface between layers of 1.8 to 2.3 m sucrose by isopycnic nonlinear sucrose density gradient centrifugation or in 1.95 m sucrose on a linear gradient. Chloroplasts, located by chlorophyll, and mitochondria by cytochrome c oxidase, were in 1.3 to 1.8 m sucrose.In leaf homogenates from the first 7 species with photorespiration, glycolate oxidase activity ranged from 0.5 to 1.5 mumoles x min(-1) x g(-1) wet weight or a specific activity of 0.02 to 0.05 mumole x min(-1) x mg(-1) protein. Glyoxylate reductase activity was comparable with glycolate oxidase. Catalase activity in the homogenates ranged from 4000 to 12,000 mumoles x min(-1) x g(-1) wet weight or 90 to 300 mumoles x min(-1) x mg(-1) protein. Specific activities of malate dehydrogenase and cytochrome oxidase are also reported. In contrast, homogenates of corn and sugarcane leaves, without photorespiration, had 2 to 5% as much glycolate oxidase, glyoxylate reductase, and catalase activity. These amounts of activity, though lower than in plants with photorespiration, are, nevertheless, substantial.Peroxisomes were detected in leaf homogenates of all plants tested; however, significant yields were obtained only from the first 5 species mentioned above. From spinach and sunflower leaves, a maximum of about 50% of the marker enzyme activities was found to be in these microbodies after homogenization. The specific activity for peroxisomal glycolate oxidase and glyoxylate reductase was about 1 mumole x min(-1) x mg(-1) protein; for catalase. 8000 mumoles x min(-1) x mg(-1) protein, and for malate dehydrogenase, 40 mumoles x min(-1) x mg(-1) protein. Only small to trace amounts of marker enzymes for leaf peroxisomes were recovered on the sucrose gradients from the last 5 species of plants. Bean leaves, with photorespiration, had large amounts of these enzymes (0.57 mumole of glycolate oxidase x min(-1) x g(-1) tissue) in the soluble fraction, but only traces of activity in the peroxisomal fraction. Low peroxisome recovery from certain plants was attributed to particle fragility or loss of protein as well as to small numbers of particles in such plants as corn and sugarcane.Homogenates of pigweed leaves (no photorespiration) contained from one-third to one-half the activity of the glycolate pathway enzymes as found in comparable preparations from spinach leaves which exhibit photorespiration. However, only traces of peroxisomal enzymes were separated by sucrose gradient centrifugation of particles from pigweed. Data from pigweed on the absence of photorespiration yet abundance of enzymes associated with glycolate metabolism is inconsistent with current hypotheses about the mechanism of photorespiration.Most of the catalase and part of the malate dehydrogenase activity was located in the peroxisomes. Contrary to previous reports, the chloroplast fractions from plants with photo-respiration did not contain a concentration of these 2 enzymes, after removal of peroxisomes by isopycnic sucrose gradient centrifugation.     

植物叶片衰老的表观遗传调控

叶片是植物重要的光合器官, 它的衰老由外界环境刺激和内源发育信号所启动, 复杂的基因调控网络参与衰老过程的精确调控。最新研究表明, 植物通过对基因表达的重编程, 在表观遗传水平上调节着叶片衰老过程。该文简要介绍了表观遗传的分子机制, 在此基础上重点综述了组蛋白修饰、染色质重塑、DNA甲基化及小RNAs途径对叶片衰老调控的最新研究进展, 同时讨论了该领域存在的问题和未来研究方向。     

泡桐愈伤组织再生植株的诱导与培养

首先以MS为基本培养基从 1 8个不同浓度的NAA和BA组合中 ,找出了毛泡桐 (Paulowniatomen tosa)、南方泡桐 (Pauiowniaaustralis)、白花泡桐 (Paulowniafortunei)、兰考泡桐 (Paulowniaelongata)和豫杂一号泡桐 (Paulowniatomentosa×P .fortunei)叶片愈伤组织诱导芽分化最适培养基分别为MS 0 .3NAA 1 2BA、MS 0 .3NAA 1 2BA、MS 0 .5NAA 1 2BA、MS 0 .5NAA 1 2BA和MS 0 .7NAA 1 2BA ;然后 ,筛选出了 5种泡桐芽诱导根的最适培养基 (分别为 1 /2MS 0 .1NAA、1 /2MS 0 .1NAA、1 /2MS、1 /2MS 0 .3NAA和 1 /2MS 0 .5NAA)。这些结果为利用不同种泡桐的原生质体融合培育泡桐新品种奠定了一定的基础。     

Leaf Regulation of the Nitrogen Concentration in the Grain of Wheat Plants

The regulation of the final grain N concentration in wheat (Triticumaestivum) plants was studied through the alteration of the source/sinkratio. Plants were grown in a greenhouse in pots with soil,and fertilized with a supraoptimal N supply. The plants were divided into six groups. In one treatment, plantsremained untouched as a control (Treatment 1). In another group,all the ears except that of the main tiller were removed atflowering (Treatment 2). All other plants were de-tillered afterthe emergence of the third leaf, leaving only one tiller perplant. At flowering, one plant set was left untouched (Treatment3). In a second group, all the leaves were excised (Treatment4). In another group half the spikelets of the ear were excised(Treatment 5) and in the last group three-quarters of the spikeletswere excised (Treatment 6). Ear excision produced an increase in individual grain weightand the grain N concentration above the normal N concentrationobserved in this cultivar. The final N concentration was correlatedwith the concentration of free amino acids in the flag leaf34 d after flowering. It is concluded that in intact plants grain protein synthesisis substrate-limited by the amino acid export pool in the leaves,and grain excision increases the availability of amino acidsto be transported to the remaining grains. Key words: Amino acids, grain N concentration, nitrogen, remobilization, wheat     

植物叶色形成调控机制研究进展

彩叶植物具有色彩鲜艳、观赏期长等特点,有助于提高城市绿化的观赏性.叶绿素、类胡萝卜素和花青素等天然色素的含量变化使叶片产生绿色、黄色、白色和紫红色等颜色,3种色素在光反应、响应生物和非生物胁迫中发挥重要作用.本文对影响叶绿素、类胡萝卜素和花青素生物合成途径遗传调控和外部环境因子综述,为解释叶片呈色机制提供理论基础.现有...     

中国瓦韦属药用植物的叶表皮观察

利用光学显微镜对中国瓦韦属（Lepisorus）17种药用植物及邻近2属3种植物的叶表皮微形态进行了观察。结果表明,瓦韦属药用植物不同种间的叶表皮特征具有一定的共性,表现为气孔器全部分布在叶下表皮,即全为下生气孔。此外,所研究的瓦韦属植物的基本气孔器类型为极细胞型、共环极细胞型、腋下细胞型及聚腋下细胞型。瓦韦属不同药用植物在叶表皮细胞的大小、形态、垂周壁式样以及气孔器类型、气孔器大小、气孔指数等特征上存在差异,据此可以划分为4种类型。叶表皮特征研究为中国瓦韦属药用植物的分类以及合理开发利用其药用价值提供了新的依据。     

Observations on the Three-dimensional Structure of the Leaf Cuticle in Certain Plants

The three-dimensional structure of the leaf cuticle has beenstudied microscopically on cuticular preparations from a numberof plants. The cuticle is one- to several-layered, the latterincluding, besides the epidermis, sub-epidermal layers suchas hypodermis, palisade, and spongy mesophyll.     

红树林植物叶片形态和解剖特征对叶肉导度、叶片导水率的影响

叶肉导度和叶片导水率是影响光合作用的两个重要过程,叶肉导度通过影响从气孔下腔到Rubisco酶位点的二氧化碳浓度梯度直接影响光合作用,而叶片导水率则通过影响水分供应或气孔行为来影响光合作用,然而对这两个生理过程之间的协同性研究较少。本研究选择9种红树林植物为研究对象,探讨盐生环境下植物叶肉导度和叶片导水率的协同性及其与叶片解剖结构特征之间的相关性。结果表明,9种红树林植物叶片导水率(0.78~5.83 mmol·m~(-2)·s~(-1)·MPa-1)、叶肉导度(0.06~0.36 mol·m~(-2)·s~(-1))、最大光合速率(7.23~23.71μmol·m~(-2)·s~(-1))等特征的差别较大;叶肉导度与最大光合速率呈显著正相关,而与比叶重无显著相关性,其原因是由于比叶重与叶片厚度、叶片密度不存在相关性;叶脉密度与气孔密度呈较强的相关性,说明红树林植物叶片水分运输与散失相关的叶片结构之间存在协同关系;叶片导水率不受叶脉密度影响,并且与叶肉导度、最大光合速率也不存在相关性,这很可能与红树林植物叶片的肉质化、有发达的储水组织有关,体现了红树林植物叶片结构和功能的特殊性。     

青藏高原草地双子叶植物叶片的气孔特征研究

利用光学显微镜对青藏高原29种草地双子叶植物叶片的气孔形态与数量特征进行观察及差异显著性分析,为揭示青藏高原草地双子叶植物对高原环境的适应机制及探索气孔作为辅助分类的依据奠定理论基础。结果表明:(1)青藏高原草地双子叶植物大多数种类在叶片上、下表皮均分布有气孔,气孔随机排列,气孔器多为无规则型。(2)气孔长度(SL)较小,上、下表皮的气孔平均长度分别为26.20μm与25.56μm,且气孔密度(SD)与气孔指数(SI)相对较大。(3)不同科、属、种间叶片上、下表皮的SL、SD、SI差异均极显著。(4)叶片上、下表皮的6个气孔数量特征之间具有显著相关关系。(5)上表皮的SL、SD与不同科、属、种间显著相关,下表皮除SI与物种间相关不显著外,其他指标与科、属、种间显著相关。研究认为,青藏高原草地双子叶植物独特的气孔形态与数量特征是对高寒极端环境长期适应的结果,且气孔数量特征对植物辅助分类具有重要价值。     

中国瓦韦属药用植物的叶表皮观察

利用光学显微镜对中国瓦韦属(Lepisorus)17种药用植物及邻近2属3种植物的叶表皮微形态进行了观察。结果表明,瓦韦属药用植物不同种间的叶表皮特征具有一定的共性, 表现为气孔器全部分布在叶下表皮, 即全为下生气孔。此外, 所研究的瓦韦属植物的基本气孔器类型为极细胞型、共环极细胞型、腋下细胞型及聚腋下细胞型。瓦韦属不同药用植物在叶表皮细胞的大小、形态、垂周壁式样以及气孔器类型、气孔器大小、气孔指数等特征上存在差异, 据此可以划分为4种类型。叶表皮特征研究为中国瓦韦属药用植物的分类以及合理开发利用其药用价值提供了新的依据。     

中国稻属植物叶片亚显微结构比较研究

用扫描电镜对原产中国的3种野生稻和2个栽培稻品种的叶片表面亚显微结构,尤其是气孔列数、气孔频度、气孔器乳突、大瘤状乳突、小栓细胞乳突等进行比较研究。结果显示,气孔频度的变化趋势是沿着疣粒野生稻-药用野生稻-栽培稻IR36-簿通野生稻-栽培稻珍汕97逐渐增大,其变化幅度在635-1737个／mm^2之间;气孔器乳突除疣粒野生稻为6个外,其余通常为4个;疣粒野生稻既无大瘤状乳突亦无木栓细胞乳突．药用野生稻无木栓细胞乳突。这些性状不仅具什种的特异性,而且与亲缘关系远近有关,可以作为稻属分类的依据。