活性氧、自由基与植物的衰老

介绍近 1 0年来有关活性氧、自由基的产生 ,对植物的伤害及植物对活性氧、自由基清除的研究进展。  

水稻叶片的衰老与超氧物歧化酶活性及脂质过氧化作用的关系

研究了从抽穗开花到籽粒成熟过程中,水稻植株顶部三片叶子的超氧物歧化酶(SOD),脂质过氧化产物丙二醛(MDA)含量及二磷酸核酮糖羧化酶活性的变化。实验结果表明:叶片的衰老伴随着 SOD 活性、RuBP 羧化酶活性及叶绿素含量的降低、丙二醛含量显著增高。分离了三个 SOD 的同工酶,证明为 Cu—Zn SOD。观察了 SOD 同工酶在叶片老化及酶液存放不同时间中的变化。讨论了叶片衰老过程中氧自由基对酶及质膜的损伤影响。  

Activation and signaling of the p38 MAP kinase pathway

The family members of the mitogen-activated protein (MAP) kinases mediate a wide variety of cellular behaviors in response to extracellular stimuli. One of the four main sub-groups, the p38 group of MAP kinases, serve as a nexus for signal transduction and play a vital role in numerous biological processes. In this review, we highlight the known characteristics and components of the p38 pathway along with the mechanism and consequences of p38 activation. We focus on the role of p38 as a signal transduction mediator and examine the evidence linking p38 to inflammation, cell cycle, cell death, development, cell differentiation, senescence and tumorigenesis in specific cell types. Upstream and downstream components of p38 are described and questions remaining to be answered are posed. Finally, we propose several directions for future research on p38.  

小麦旗叶自然衰老过程中清除活性氧能力的变化

野生一粒小麦(Triticum boeoticum Boiss)、栽培小麦“扬麦五号”(T.aestivum L.)的旗叶自然衰老过程中,活性氧清除系统中各部分的清除能力下降是不均衡的。在光合速率高值持续期(叶绿素含量缓降期),SOD的活力略有下降,过氧化氢酶(CAT)活力却迅速下降,同时抗坏血酸过氧化物酶(ASP)活力呈现先上升后下降的趋势,上述SOD、CAT、ASP活力变化的不均衡,最终导致H_2O_2的迅速累积,从而使叶片迅速进入衰老(叶绿素含量速降期),于是SOD活力迅速下降。野生一粒小麦活性氧清除系统中各部分清除能力失衡过快,可能是其早衰的原因之一。H_2O_2的迅速累积与叶片衰老的启动密切相关。  

衰老叶片和叶绿体中H_2O_2的累积与膜脂过氧化的关系

在自然衰老和ABA处理的叶片和叶绿体中活性氧H_2O_2均比对照明显增高。外加H_2O_2刺激水稻叶绿体膜脂过氧化作用。叶绿体的丙二醛含量随H_2O_2浓度、光照时间、光照强度及叶绿体完整性而变化。AsA、GSH、SOD、甘露醇和过氧化氢酶对外源H_2O_2引起的膜脂过氧化有缓解作用,Fe~(2+)有刺激作用。而H_2O_2对叶绿体过氧化损伤主要是转化为OH之故。  

高等植物叶片的衰老

蛋白质丧失是叶片衰老的一个早期表现，降解的蛋白主要是可溶性蛋白中部分Ⅰ蛋白，随衰老加深，叶绿素含量、光合速率下降，保护酶活性降低。叶片这些衰老的表现是体内活性氧、自由基代谢失调累积的结果。  

细胞分裂素在植物抗逆和延衰中的作用

本文综述了细胞分裂素类物质的种类、分布和在植物抗水分胁迫、低温冷害、病虫害等方面的作用以及在延缓果实、叶片、切花等衰老中的效果，讨论了其生理机制、细胞分裂素与其它植物激素的相互关系，并提出了有关细胞分裂素类物质作用机理中值得深入研究的若干问题，如嘌呤型与苯基脲型细胞分裂素的作用特点，细胞分裂素与生长素、脱落酸的协调作用和拮抗作用细胞分裂素的从头合成途径和tＲＮＡ途径等。  

植物叶片衰老与氧化胁迫

叶片衰老是叶片生长发育进程中的最后阶段，与活性氧伤害有着密切的关系。介绍了植物叶片衰老过程中活性氧产生及清除系统的变化，讨论了对水分胁迫与氧化胁迫的交叉抗性，并对下一步的研究作出了展望  

The role of hexokinase in plant sugar signal transduction and growth and development

Previous studies have revealed a central role of Arabidopsis thaliana hexokinases (AtHXK1 and AtHXK2) in the glucose repression of photosynthetic genes and early seedling development. However, it remains unclear whether HXK can modulate the expression of diverse sugar-regulated genes. On the basis of the results of analyses of gene expression in HXK transgenic plants, we suggest that three distinct glucose signal transduction pathways exist in plants. The first is an AtHXK1-dependent pathway in which gene expression is correlated with the AtHXK1-mediated signaling function. The second is a glycolysis-dependent pathway that is influenced by the catalytic activity of both AtHXK1 and the heterologous yeast Hxk2. The last is an AtHXK1-independent pathway in which gene expression is independent of AtHXK1. Further investigation of HXK transgenic Arabidopsis discloses a role of HXK in glucose-dependent growth and senescence. In the absence of exogenous glucose, plant growth is limited to the seedling stage with restricted true leaf development even after a 3-week culture on MS medium. In the presence of glucose, however, over-expressing Arabidopsis or yeast HXK in plants results in the repression of growth and true leaf development, and early senescence, while under-expressing AtHXK1 delays the senescence process. These studies reveal multiple glucose signal transduction pathways that control diverse genes and processes that are intimately linked to developmental stages and environmental conditions.  

Drought induces oxidative stress in pea plants

Pea (Pisum sativum L. cv. Frilene) plants subjected to drought (leaf water potential of -1.3 MPa) showed major reductions in photosynthesis (78), transpiration (83), and glycolate oxidase (EC 1.1.3.1) activity (44), and minor reductions (18) in the contents of chlorophyll a, carotenoids, and soluble protein. Water stress also led to pronounced decreases (72–85) in the activities of catalase (EC 1.11.1.6), dehydroascorbate reductase (EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2), but resulted in the increase (32–42) of non-specific peroxidase (EC 1.11.1.7) and superoxide dismutase (EC 1.15.1.1). Ascorbate peroxidase (EC 1.11.1.11) and monodehydroascorbate reductase (EC 1.6.5.4) activities decreased only by 15 and the two enzymes acted in a cyclic manner to remove H₂O₂, which did not accumulate in stressed leaves. Drought had no effect on the levels of ascorbate and oxidized glutathione in leaves, but caused a 25 decrease in the content of reduced glutathione and a 67 increase in that of vitamin E. In leaves, average concentrations of catalytic Fe, i.e. Fe capable of catalyzing free-radical generation by redox cycling, were estimated as 0.7 to 7 M (well-watered plants, depending on age) and 16 M (water-stressed plants); those of catalytic Cu were 4.5 M and 18 M, respectively. Oxidation of lipids and proteins from leaves was enhanced two- to threefold under stress conditions and both processes were highly correlated. Fenton systems composed of the purported concentrations of ascorbate, H₂O₂, and catalytic metal ions in leaves produced hydroxyl radicals, peroxidized membrane lipids, and oxidized leaf proteins. It is proposed that augmented levels and decompartmentation of catalytic metals occurring during water stress are responsible for the oxidative damage observed in vivo.Abbreviations and Symbol ASC ascorbate - DW dry weight - DHA dehydroascorbate - GSH reduced glutathione - GSSG oxidized glutathione - MDHA monodehydroascorbate (ascorbate free radical) - SOD Superoxide dismutase - _wa water potential We thank Dr. R. Picorel (E.E. de Aula Dei, CSIC) for allowing us access to HPLC equipment. J.F.M., 1.1., and S.F. were the recipients of predoctoral fellowships from the Comunidades Autónomas de Aragon, Pais Vasco, and Navarra, respectively. R.V.K. thanks the U.S. Department of Agriculture (grant 91-37305-6705) for travel support. This work was financed by grants from the Comisión Interministerial de Ciencia y Tecnología (AGR-91-0857-C02 to P.A. and M.B.) and the Dirección General de Investigación Científica y Técnica (PB92-0058 to M.B) of Spain.