Salinity-induced subcellular accumulation of H2O2 in leaves of rice

The localization of salt-induced H2O2 accumulation in the leaves of rice was examined using 3,3-diaminobenzidine and CeCl3 staining at ultrastructure level. When the 3-week-old rice plants were affected by 100 mM NaCl for 14 days, the swelling of thylakoids and the destruction of thylakoid membranes were observed. H2O2 accumulation was also observed in the chloroplast of the leaf treated with NaCl. The electron dense products of 3,3-diaminobenzidine and CeCl3 were mainly observed especially around the swelling of thylakoids. H2O2 accumulation and any ultrastructural changes were not observed in the chloroplasts under dark condition. Furthermore, treatment with ascorbic acid suppressed both H2O2 accumulation and the changes in chloroplast ultrastructure. These results suggest that light-induced production of excess H2O2 under salinity is responsible for the changes in chloroplast ultrastructure. H2O2 accumulation was also observed in the mitochondria, peroxisomes, plasma membrane, and cell walls under light but not dark, suggesting that these organelles are also the source of H2O2 and the production is light dependent under salinity.