Exogenous Sodium Nitroprusside Alleviates Salt-Induced Changes in Photosynthesis of Greenhouse Tomato Plants by Leaf Age-Dependent Manner

Abstract Photosynthesis is one of the main processes affected by salinity. Salt stress limits the availability of CO 2 by restricting its diffusion through stomata; leads to chlorophyll degradation, damage to light-harvesting complexes, suppression of PSII activity and reduced biomass production. Nitric oxide (NO) is an important signalling molecule with many physiological functions. NO can alleviate salt-induced changes in photosynthesis. However, the role of NO in the photosynthetic apparatus (especially PSI) of salt-stressed plants is poorly understood, especially at different leaf ages. Our results showed that the effect of exogenous NO donor sodium nitroprusside (SNP) application on photosynthetic performance measured by Dual-PAM and LI-COR portable photosynthesis system in tomato leaves was dependent on leaf developmental stage. After one week, 0.1 mM SNP treatments via the rooting medium significantly attenuated the decrease in photosynthetic parameters, especially in young leaves, such as leaf chlorophyll content, net photosynthetic rate, stomatal conductance, effective quantum yield of PSII and PSI, and counteracted the increase in the quantum yield of regulated non-photochemical quenching [Y(NPQ)] and cyclic electron flow [Y(CEF)]. At the same time, salt stress-induced deleterious effects were the most pronounced in old leaves based on changes in biomass, maximum PSII quantum yield (Fv/Fm), photosynthetic pigment loss and lipid peroxidation, which were only partially alleviated by SNP. The results showed that exogenous application of SNP improved photosynthetic performance in salt-stressed tomato plants in a leaf level-dependent manner and was the most effective in young, developing leaves, which was associated with an increase in PSII and PSI efficiency.