Nitric oxide alleviates cadmium toxicity in tall fescue photosystem II on the electron donor side

Tall fescue (Festuca arundinacea) possesses remarkable prospects in heavy metal phytoremediation. Nitric oxide (NO) plays multifunctional roles in plant growth, development and the regulation of cellular mechanisms. In this study, we evaluated the potential use of tall fescue for cadmium (Cd) phytoremediation and the contribution of NO to the process. Different concentrations of Cd2+ were applied to study the toxic effects of Cd2+ and its absorption in tall fescue. Sodium nitroprusside (SNP) was used as exogenous NO donor and NG-nitro-l-arginine-methyl ester (L-NAME) was used as a NO synthesis inhibitor to evaluate the role of NO in tall fescue phytoremediation. The tall fescue growth parameters and photosystem II (PSII) activities were determined. The performance of the tall fescue was inhibited by an increase in the Cd2+ concentration. The SNP treatment improved the behaviour of tall fescue against Cd2+ stress, while the L-NAME treatment led to the opposite results in certain cases. Additionally, SNP treatment reduced the Cd2+ contents of the tall fescue shoots. The study of OJIP curves showed that Cd2+ treatment possessed negative effects on PSII grouping and NO treatment could alleviate Cd2+ toxicity on PSII. Moreover, JIP test depicted toxic effect of Cd2+ upon tall fescue and the protective role of NO against heavy metal stress. Overall, the tall fescue exhibited high tolerance to Cd2+ stress and NO protected the fescue from Cd2+. Cd2+ toxicity in the tall fescue PSII is primarily localized on the electron donor side. NO alleviated Cd2+ toxicity on the PSII electron donor side, which may be due to its role in the regulation of the level and toxicity of reactive oxygen species.