Nitric Oxide And Hydrogen Peroxide And Its Mechanism Of Rice Seedlings Under Salt Stress

Salt stress has a deleterious effect on plant growth and development and its mechanism is largely unknown at present. Accumulative evidence indicates that nitric oxide (NO) and hydrogen peroxide (H₂O₂), as signaling molecules, are involved in the regulation of plant growth and development. In the present study, the effects of NO and H₂O₂ on the growth of seedlings of salt-stressed rice plants and its possible mechanisms were investigated using Indica rice (Oryza sativa L. cv. 9311). The main results were presented as follows:NaCl treatment inhibited seedling growth. Treatments with 0.01-1.00mmol/L SNP or low concentrations (0.01-0.05mmol/L) of H₂O₂ could alleviate the inhibitory effects of NaCl. Leaf growth rate, fresh weight and dry weight of shoot and relative water content increased when the rice seedlings was treated with above concentrations of SNP or H₂O₂ under salt stress, and the effect of 0.01mmol/L SNP or 0.05mmol/L H₂O₂ was the most obvious. On the contrary, higher concentrations (0.50-1.00mmol/L) of H₂O₂ displayed significant toxic effect to rice growth.Application of NO scavenger (hemoglobin, Hb) and H₂O₂ scavenger (dimethylthiourea, DMTU) decreased leaf growth rate, fresh weight and dry weight of shoot and leaf relative water content of NaCl-treated rice seedlings. 0.5% Hb treatment reverted SNP-enhanced effect on rice seedling growth under salt stress, suggesting NO is the effective factor. The concentration of H₂O₂ increased constantly and that of NO increased first and then decreased in rice seedlings with the prolongation of salt stress as compared with the control treatment (without NaCl treatment). These results suggested NO and H₂O₂ were included in the reponse to salt stress of rice seedlings.Net photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO₂ concentration were decreased with the treatment of 100mmol/L NaCl. The photosynthesis of the leaves of salt-stressed rice were significantly enhanced with the inclusion of 0.01mmol/L SNP or 0.05mmol/L H₂O₂. The levels of net photosynthetic rate, transpiration rate and intercellular CO₂ concentration in the rice seedlings treated with exogenous NO or H₂O₂ were increased more significantly than in those without NO or H₂O₂, however, stomatal conductance did not change significantly.