Rapid Inactivation of Chloroplastic Ascorbate Peroxidase is Responsible for Oxidative Modification to Rubisco in Tomato (Lycopersicon esculentum) under Cadmium Stress  

作　　者：Kai-Lang Liu Lin Shen Jia-Qi Wang Ji-Ping Sheng 

机构地区：[1]College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China [2]State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100094, China

出　　处：《Journal of Integrative Plant Biology》2008年第4期415-426,共12页植物学报（英文版）

基　　金：the National Natural Science Foundation of China (30671471and 30571296)

摘　　要：To investigate the sensitive site of antioxidant systems in chloroplast under cadmium stress and its consequence on reactive oxygen species production and action, the sub-organellar localization of chloroplast superoxide dismutases （SOD, EC 1.15.1.1） and ascorbic peroxidase （APX, EC 1.11.1.11） isoenzymes and changes of enzymes activities under cadmium stress were investigated in tomato seedlings. Two APX isoforms, one thylakoid-bound and one stromal, were detected. Cd at 50 μM induced a moderate increase of SOD activities but a rapid inactivation of both APX isoenzymes. APX inactivation was mainly related to the decrease of ascorbate concentration, as supported by in vitro treatment of exogenous ascorbate and APX kinetic properties under Cd stress. H2O2 accumulation in chloroplast, as a consequence of APX inactivation, was associated with a 60% loss of Rubisco （EC 4.1.1.39） activity, which could be partially accounted for by a 10% loss of Rubisco content. Protein oxidation assay found that the Rubisco large subunit was the most prominent carbonylated protein; the level of carbonylated Rubisco large subunit increased fivefold after Cd exposure. Thiol groups in the Rubisco large subunit were oxidized, as indicated by non-reducing electrophoresis. Treating crude extract with H2O2 resulted in a similar pattern of protein oxidation and thiols oxidation with that observed in Cd-treated plants. Our study indicates that APXs in the chloroplast is a highly sensitive site of antioxidant systems under Cd stress, and the inactivation of APX could be mainly responsible for oxidative modification to Rubisco and subsequent decrease in its activity.To investigate the sensitive site of antioxidant systems in chloroplast under cadmium stress and its consequence on reactive oxygen species production and action, the sub-organellar localization of chloroplast superoxide dismutases （SOD, EC 1.15.1.1） and ascorbic peroxidase （APX, EC 1.11.1.11） isoenzymes and changes of enzymes activities under cadmium stress were investigated in tomato seedlings. Two APX isoforms, one thylakoid-bound and one stromal, were detected. Cd at 50 μM induced a moderate increase of SOD activities but a rapid inactivation of both APX isoenzymes. APX inactivation was mainly related to the decrease of ascorbate concentration, as supported by in vitro treatment of exogenous ascorbate and APX kinetic properties under Cd stress. H2O2 accumulation in chloroplast, as a consequence of APX inactivation, was associated with a 60% loss of Rubisco （EC 4.1.1.39） activity, which could be partially accounted for by a 10% loss of Rubisco content. Protein oxidation assay found that the Rubisco large subunit was the most prominent carbonylated protein; the level of carbonylated Rubisco large subunit increased fivefold after Cd exposure. Thiol groups in the Rubisco large subunit were oxidized, as indicated by non-reducing electrophoresis. Treating crude extract with H2O2 resulted in a similar pattern of protein oxidation and thiols oxidation with that observed in Cd-treated plants. Our study indicates that APXs in the chloroplast is a highly sensitive site of antioxidant systems under Cd stress, and the inactivation of APX could be mainly responsible for oxidative modification to Rubisco and subsequent decrease in its activity.

关 键 词：ascorbate peroxidase CADMIUM hydrogen peroxide protein oxidation Rubisco. 

分 类 号：Q94[生物学—植物学]