Role of Hydrogen peroxide (H2O2) in sensing and signalling abiotic stimuli in rice

Abstract

This dissertation describes the integration of physiological, proteomic, and metabolomic changes in conjunction with the synthesis of H2O2 under various stress conditions in rice, Oryza sativa (Japonica var. Koshihikari). Dynamics of H2O2 production were observed in the leaves following the treatment with drought, salinity, osmotic and cold stress. The physiological parameters such as H2O2 content, photosynthetic activity, water content, and lipid peroxidation were used as indicators to correlate the physiological status of the plant with its metabolites and proteins profile/changes in response to stresses. A targeted proteomic approach has been developed to identify oxidative modified thiols, and a NMR-based analysis has been performed for metabolites profiling. Activation of amino acids was observed in the treatment of short-term drought stress while deficit of sugar and lipids in addition to accumulation of amino acids were observed when treated with long-term drought stress. The high levels of lipid peroxidation and the irreversible oxidation of protein thiols observed under long-term drought stress indicate that the plants were likely to have suffered membrane damage. In osmotic stress treatment, the plants showed rapid dehydration compared to that treated with drought stress. The transient increase of both lipid peroxidation and reversible thiol oxidation suggest that signalling of adaptation had been activated, resulting in fluctuation of carbon and nitrogen metabolism in the plants. In salinity stress treatment, very low levels of lipid peroxidation, decline in photosynthetic activities, and very few metabolites changes were observed. This suggests that the dosage used in salinity test was insufficient to induce salt stress to the plants. Another possibility is that the changes in thiol proteins following the salt treatment were likely to have contributed to salt tolerance, hence keeping the metabolites in the control level. Moreover, the metabolite changes observed in the plants following exposure to exogenous H2O2 was found to overlap with those induced by other stresses, indicating that H2O2 is likely to have effects on the carbohydrate, fatty acid, and amino acids pathways. In summary, the results suggest that there were possible overlap of H2O2 mediated-signalling pathway in coordinating cellular changes at both proteomic and metabolomic level under abiotic stress conditions in rice plants. However, further studies are needed to confirm the role and the underlying mechanism of H2O2 in regulating the cellular changes.