Metabolism of lipid peroxide-derived aldehydes in chloroplasts and their physiological roles in environmental stress

高温、干旱和UV-B等环境胁迫通常会导致叶绿体中活性氧的产生增加，从而导致叶细胞的氧化损伤。近年来，脂质过氧化物衍生的醛类化合物已被公认为介导细胞损伤，但其在植物中的代谢和毒理学研究较少。在这项研究中，我们调查（i）脂质过氧化物衍生的醛类在叶绿体中的代谢和（ii）这些醛类在植物响应环境胁迫的生理作用。结果表明：（1）不同种类的醛对离体叶绿体的CO_2固定有不同程度的失活作用。2-烯醛的毒性高于正链烷醛。丙烯醛和4-羟基壬烯醛的毒性最大。卡尔文循环中的几种酶受到2-烯醛的影响，但类囊体电子传递链受到的影响要小得多。(2)在叶绿体中添加谷氨酰胺可延缓叶绿素诱导的CO_2-fi损失 关于我们 抗坏血酸则不然，这表明谷胱甘肽对乙醛有特殊作用。从叶绿体的不同区室中提取醛，用2，4-二硝基苯肼衍生化，并用HPLC测定。脂氧合酶途径依赖的C6醛的主要成分中发现的信封和基质。类囊体含有更多种类的醛，包括高毒性的2-烯醛和4-羟基-2-烯醛，表明类囊体中醛的非酶（活性氧介导的）产生。(3)将亚麻酸缺陷拟南芥突变体中的醛组成与野生型中的醛组成进行比较。丙烯醛、丙醛、丙二醛和2 E-戊烯醛是由亚麻酸衍生的。(4)拟南芥植株在热胁迫或强光照射下，叶绿体中几种酶的去乙酰化修饰增加。其中一个丙二醛修饰的蛋白质是OEC 33蛋白，表明在管腔中产生丙二醛。因此，热或光胁迫诱导叶绿体中脂质过氧化物产生高毒性醛，导致卡尔文循环失活。谷氨酸是一种非常重要的醛类解毒剂。少

Environmental stresses such as heat, drought and UV-B commonly lead to oxidative damage in leaf cells due to enhanced production of reactive oxygen species in chloroplasts. Recently, lipid peroxide-derived aldehydes have been recognized to mediate cell injury, but their metabolism and toxicology in plants are poorly investigated. In this study we investigated (i) the metabolism of lipid peroxide-derived aldehydes in the chloroplast and (ii) the physiological roles of those aldehydes in the plant responses to environmental stresses. We have obtained the following results : (1) Various species of aldehydes inactivated the CO2-fixation in isolated chloroplasts in vitro. The toxicity was higher for 2-alkenals than n-alkanals. Acrolein and 4-hydroxynonenal showed the greatest toxicity. Several enzymes in the Calvin cycle by 2-alkenals, but the thylakoid electron transport chain was much less affected. (2) Glutathione supplemented to chloroplasts retarded the aldehyde-induced loss of CO_2-fi … More xation, but ascorbate did not, showing the specific role of glutathione to scavenge aldehydes. Aldehydes were extracted from distinct compartments in the chloroplast, derivatized with 2,4-dinitrophenylhydrazine and determined with HPLC. Lipoxygenase pathway-dependent C6 aldehydes were major components found in envelopes and stroma. Thylakoids contained greater variety of aldehydes, including highly toxic 2-alkenals and 4-hydroxy-2-alkenals, suggesting non-enzymatic(reactive oxygen species-mediated)production of aldehydes in thylakoids. (3) Aldehyde composition in the linolenic acid-deficient Arabidopsis mutant was compared with that in wild type. Acrolein, propionaldehyde malondialdehyde and 2E-pentenal were derived from linolenic acid. (4) When Arabidopsis plants were heat stressed or tobacco leaves were strongly illuminated, aldehyde-modification of several chloroplast enzymes in them were increased. One of the malondialdehyde-modified proteins was OEC33 protein, suggesting the production of malondialdehyde in the lumen. Thus heat- or light-stress induces the production highly toxic aldehydes from lipid peroxides in chloroplasts, leading to inactivation of the Calvin cycle. Glutathione is a critically important detoxicant against aldehydes. Less