Attenuation of salt-induced changes in photosynthesis by exogenous nitric oxide in tomato (Lycopersicon esculentum Mill. L.) seedlings

Exogenous sodium nitroprusside (SNP), a NO donor, was applied in this  study to investigate the potential role of NO in photosynthetic performance of tomato ( Lycopersicon esculentum L. cv. Hufan2560) seedlings under salt-stressed conditions. Exogenous NO alleviated the decrease in dry mass of shoot and root caused by salt stress. In parallel, NO application in salt-stressed plants attenuated the decrease in the photosynthetic parameters such as leaf chlorophyll, net photosynthetic rate (P N ), stomatal conductance (gs), transpiration rate (E), the ratio of variable to maximum fluorescence (Fv/Fm), electron transport rate  (ETR), the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (Fv´/Fm´), and the photochemical quenching coefficient (qP), and counteracted the increase in on-photochemical quenching coefficient (qN). Furthermore, the changes as mentioned above reversed by NO treatment are specific to salt stress since application of NO alone to tomato seedlings without salt stress had slight effects on the tested parameters. The results obtained here demonstrated that the photosynthetic performance was improved by NO application in salt-stressed plants and such an improvement was associated with an enhancement of gas-exchange and the actual PSII efficiency, which revealed an important role of NO in enhancing  resistance of plants to salt stress. Keywords : Nitric oxide, photosynthesis, salt stress, Lycopersicon esculentum L., stomatal conductance, transpiration rate