Exogenous nitric oxide enhances salt tolerance in tomato (Lycopersicon esculentum Mill.) by improving photosynthetic performance and modulating the expression of photosystem II genes

Nitric oxide (NO) is an important redox signaling molecule involved in a diverse range of physiological processes including response to environmental stresses. The present study aims to investigate the effects of NO application on the photosynthetic performance of tomato seedlings under salt stress. Different concentrations of sodium chloride (0, 50, 100, and 200 mu M) and the NO donor, sodium nitroprusside (SNP) (0, 100, and 200 mu M) were applied to the tomato seedlings. Effects on Photosynthetic parameters were analyzed by chlorophyll a fluorescence induction technique and JIP-test. Expression changes of three key PSII genes were examined by real-time PCR. The results revealed that salt stress impaired different photosynthetic parameters including light absorbance and energy trapping, yields and efficiencies of electron transport, and performance indices of photosynthetic apparatus. The Transcript of psbP, psbO, and psbW involved oxygen-evolving complex was significantly downregulated in response to salt stress. SNP application alleviated the salt stress damage to the photosynthetic apparatus of tomato seedlings and improved different stages of the photosynthetic process, from light absorption to energy transfer and electron transport and gene expression pattern. The 100 mu M SNP proved to be the optimal concentration to improve photosynthetic performance under salt stress.