Salicylic acid response in rice: influence of salicylic acid on H 2O 2 accumulation and oxidative stress

Abstract

We have studied the accumulation of hydrogen peroxide in rice leaves in response to salicylic acid (SA) treatment. H 2O 2 accumulation was localized in the veins. While the activity of the H 2O 2 degrading enzyme peroxidase was inhibited in response to SA, superoxide dismutase activity, which generates H 2O 2, did not show any change. An increase in the activity of glutathione reductase, a peroxide degrading enzyme, was observed upon SA treatment, similar to the response reported by accumulation of active oxygen species. In rice leaves transformed with CaMV-GUS fusions, we found that SA treatment induced transcriptional activation through as-1 element. As-1 has been implicated in protective mechanisms that operate during some types of oxidative stress and the hypersensitive response (HR). Expression of rice pathogenesis-related protein 5 (PR5), one of the PR genes associated with systemic acquired resistance, was induced by SA. This induction seems to be independent of the H 2O 2 accumulation induced by SA. Inoculation of rice leaves with the rice blast fungus, Magneporthe grisea, also led to the accumulation of H 2O 2 in the veins, suggesting the presence of common signals between SA and pathogen responses. Thus SA application seems to induce oxidative stress in rice through H 2O 2; a signal molecule implicated in biotic and abiotic stress responses.