Nitric oxide counteracts the senescence of rice leaves induced by hydrogen peroxide

In the present study, we evaluate the protective effect of nitric oxide (NO) against the senescence of rice leaves promoted by hydrogen peroxide (H 2 O 2 ). Senescence of rice leaves was determined by decreases in protein content. H 2 O 2 treatment resulted in (1) increases in leaf H 2 O 2 content, (2) induction of leaf senescence, (3) increases in lipid peroxidation, (4) decreases in ascorbic acid (AsA) and reduced form glutathione (GSH) contents, and (5) increases in antioxidative enzyme activities (ascorbate peroxidase, glutathione reductase, and peroxidase). NO donors [N-tert-butyl-α-phenylnitrone (PBN), sodium nitroprusside, 3-morpholinosydonimine, and AsA + NaNO 2 ] were effective in reducing H 2 O 2 -induced leaf senescence. PBN prevented H 2 O 2 -increased H 2 O 2 content, H 2 O 2 -induced lipid peroxidation, H 2 O 2 -decreased AsA and GSH contents, and H 2 O 2 -increased antioxidative enzyme activities. The protective effect of PBN on H 2 O 2 -promoted senescence, H 2 O 2 -increased H 2 O 2 content and lipid peroxidation, H 2 O 2 decreased AsA and GSH contents, and H 2 O 2 -increased antioxidative enzyme activities was reversed by 2(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a NO-specific scavenger, suggesting that the protective effect of PBN is attributable to the NO released. Reduction of H 2 O 2 -induced senescence by NO in rice leaves is most likely mediated through its ability to scavenge H 2 O 2 .