Effects of exogenous nitric oxide on some photosynthetic parameters in tomato (Lycopersicon esculentum L.) under salinity stress

Photosynthesis is one of the most important physiological processes that is negatively affected by salinity stress in plants. Nitric oxide is known as an influential signal molecule in plant responses to environmental stresses. The tomato plant (Lycopersicon esculentum L.) contains a wide range of vitamins and nutrients that are economically and nutritionally important. In the present study, the effects of different levels of salinity stress including 0, 50, 100 and 150 mM NaCl and sodium nitroprusside (SNP) at 0, 100 and 200 μM levels on different photosynthetic parameters were investigated by JIP test. The results of this study showed that salinity stress reduced the efficiency of the oxygen-evolving complex in photosystem II. Salinity reduces the efficiency of light reactions of the photosystem II (φPo/(1-φPo)) and the efficiency index of active reaction centers (γRC/(1-γRC)). Furthermore, the efficiency of biochemical reactions of electron transport (ψo/(1- ψo)) and the efficiency index of reduction of the end electron acceptor in photosystem I (δRo/(1-δRo)) decreased with salinity stress. The results also revealed that salinity stress reduced the overall performance of the photosynthetic apparatus from the beginning of photosystem II to the end of photosystem I (PITotal). Salinity stress reduced photosynthetic pigments, including chlorophyll a, chlorophyll b and total chlorophyll, and a significant increase in total carotenoids, total polyphenolic content and total flavonoid were observed under salinity stress. The use of SNP as a nitric oxide donor mitigated the effects of salinity stress in all the mentioned parameters. The results of this study showed that in the photosynthetic apparatus of the tomato plants, the electron transport chain is the most sensitive point to salinity stress and 100 μM SNP is the most effective concentration to alleviate the effects of salinity stress.