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

高温、干旱和UV-B等环境胁迫通常通过增加叶绿体中活性氧的产生而导致叶片细胞的氧化损伤。近年来，脂质过氧化衍生的醛已被认为可以介导细胞损伤，但其在植物体内的代谢和毒理学研究较少。在这项研究中，我们研究了(I)脂质过氧化衍生的醛在叶绿体中的代谢和(Ii)这些醛在植物对环境胁迫反应中的生理作用。我们获得了以下结果：(1)不同种类的醛在体外对叶绿体的CO2固定有钝化作用。2-烷烃的毒性大于正构烷烃。丙烯醛和4-羟基壬烯醛毒性最大。Calvin循环中的几种酶受2-烯烃的影响，但类囊体电子传递链受到的影响要小得多。(2)叶绿体中添加谷胱甘肽可延缓乙醛诱导的CO_2-FI…的丢失更多的氧化，但抗坏血酸没有，显示了谷胱甘肽清除醛的特殊作用。从叶绿体的不同隔室中提取醛，用2，4-二硝基苯肼衍生化，用高效液相色谱法测定。脂氧合酶途径依赖的C6醛是包膜和基质中的主要成分。类囊体含有更多种类的醛，包括剧毒的2-烯烃和4-羟基-2-烯烃，这表明类囊体醛的产生是非酶(活性氧)介导的。(3)比较了亚麻酸缺陷型拟南芥突变体与野生型的醛组成。以亚麻酸为原料合成了丙烯醛、丙二醛和2E-戊烯醛。(4)在高温胁迫或强光照射下，拟南芥植株体内几种叶绿体酶的醛修饰增加。丙二醛修饰的蛋白之一是OEC33蛋白，这表明管腔中产生了丙二醛。因此，热或光胁迫诱导叶绿体中的过氧化脂质产生剧毒的醛，导致卡尔文循环的失活。谷胱甘肽是一种非常重要的抗醛解毒剂。较少

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