The inductive responses of the antioxidant enzymes by salt stress in the rice (Oryza sativa L.)

To access contributions of inductive responses of the antioxidant enzymes i n the resistance to salt stress, activities of the enzymes were determined in the rice (Oryza sativa L. cv. Dongjin) plant. In the leaves of the rice plant, salt stress preferentially enhanced the content of H2O2 as well as t he activities of the superoxide dismutase (SOD), ascorbate peroxidase (APX) , and peroxidase specific to guaiacol, whereas it induced the decrease of c atalase activity. On the other hand, salt stress had little effect on the a ctivity levels of glutathione reductase (GR:). In order to analyze the chan ges of antioxidant enzyme isoforms against salt stress, plant extracts were subjected to native PAGE. Leaves of the rice plant had two isoforms of Mn- SOD and five isoforms of Cu/Zn-SOD. Fe-SOD isoform was not observed in the activity gels. Expression of Cu/Zn-1,-2, and Mn-SOD-2 isoforms was preferen tially enhanced by salt stress. Seven APX isoforms were presented in the le aves of the rice plants. The intensities of APX-4 to -7 were enhanced by sa lt stress, whereas those of APX-1 to -3 were minimally in changed response to salt stress. There were seven GR isoforms in the leaves of rice plants. Levels of activity for most GR isoforms did not change in the stressed plan ts compared to the control plants. On the other hand, the levels of activit y for most antioxidant enzymes changed little in the roots of stressed plan ts compared to the control plants. These results collectively suggest that SOD leads to the overproduction of hydrogen peroxide in the leaves of rice plants subjected to salt stress: The overproduction of hydrogen peroxide fu nctions as the signal oi salt stress, which induces the induction of specif ic APX isoforms but not specific GR isoforms under catalase deactivation.