A protective role for nitric oxide and salicylic acid for arsenite phytotoxicity in rice (Oryza sativa L.).

Nitric oxide (NO) and salicylic acid (SA) are important signaling molecules in plant system. In the present study both NO and SA showed a protective role against arsenite (AsIII) stress in rice plants when supplied exogenously. The application of NO and SA alleviated the negative impact of AsIII on plant growth. Nitric oxide supplementation to AsIII treated plants greatly decreased arsenic (As) accumulation in the roots as well as shoots/roots translocation factor. Arsenite exposure in plants decreased the endogenous levels of NO and SA. Exogenous supplementation of SA not only enhanced endogenous level of SA but also the level of NO through enhanced nitrate reductase (NR) activity, whether AsIII was present or not. Exogenously supplied NO decreased the NR activity and level of endogenous NO. Arsenic accumulation was positively correlated with the expression level of OsLsi1, a transporter responsible for AsIII uptake. The endogenous level of NO and SA were positively correlated to each other either when AsIII was present or not. This close relationship indicates that NO and SA work in harmony to modulate the signaling response in AsIII stressed plants.