The Accumulation of Hydrogen Peroxide in Senescing Leaves and Chloroplasts in Relation to Lipid Peroxidation
LIN Zhi-Fang;LI Shuang-Shuan;LIN Gui-Zhu;Guo Jun-Yan South China Institute of Botany, Academia Sinica, Cuangzhou 510156
Lipid peroxidation is reported as one ofthe most deteriorative reactions that resultsin damage to membranous cellelar constituents,especially the subcellular organelles during leafsenescence. For further understanding leafsenescence in relation to lipid peroxidation, thecontent of active oxygen H_2O_2 in senescingleaves and aging chloroplasts, the effect of exo-genous H_2O_2 on lipid peroxidation of chloro-plast were studied. The content of H_2O_2, wasdetermined using Titanium (Ⅳ), and the pro-duct of lipid peroxidation, malondialdehydewas measured by thiobarbituric acid test. In senescing rice, corn and amaranth lea-ves, the content of H_2O_2 increased 90～177%,and that of chlorophyll decreased 41～62%,Moreover, the H_2O_2 contents in aging chloro-plasts and leaves treated by ABA also increasedby 28～66%, The lipid peroxidation in ricechloroplasts was stimulated by exogenous H_2O_2Light enhanced the toxicity of H_2O_2. Malon-dialdehyde content of chloroplasts increasedwith concentration of H_2O_2,light intensity andtime of illumination. In addition, the C trpechloroplast was more sensitive to H_2O_2 thanthe A type. Application of scavengers for ac-tive oxygen (H_2O_2, O, OH·) such as catalase,superoxide dismufase, glutathione, ascorbicacid and mannitol retarded lipid peroxidation,but Fe~(2+) and MV promoted markedly the for-mation of malondialdehyde under the action ofH_2O_2. The results indicate that the photoperoxi-dation damage on chloroplast induced by H_2O_2is mainly due to the formation of more activehydroxyl radicals (OH·) by Fenton reactionand Haver-Weiss reaction catalyzed by Fe~(2+)and O_2 in the chloroplast. The accumu1ationof H_2O_2 may explain the exacerbation of lipidperoxidation during leaf senescence.