The Protective Effect of Exogenous Ascorbic Acid on Photosystem Inhibition of Tomato Seedlings Induced by Salt Stress

Abstract

This study investigated the protective effects of exogenous ascorbic acid (AsA, 0.5 mmol·L−1) treatment on salt-induced photosystem inhibition in tomato seedlings under salt stress (NaCl, 100 mmol·L−1) conditions with and without the AsA inhibitor lycorine. Salt stress reduced the activities of photosystem II (PSII) and PSI. AsA treatment mitigated inhibition of the maximal photochemical efficiency of PSII (Fv/Fm), maximal P700 changes (Pm), the effective quantum yields of PSII and I [Y(II) and Y(I)], and non-photochemical quenching coefficient (NPQ) values under salt stress conditions both with and without lycorine. Moreover, AsA restored the balance of excitation energy between two photosystems (β/α-1) after disruption by salt stress, with or without lycorine. Treatment of the leaves of salt-stressed plants with AsA with or without lycorine increased the proportion of electron flux for photosynthetic carbon reduction [Je(PCR)] while decreasing the O2-dependent alternative electron flux [Ja(O2-dependent)]. AsA with or without lycorine further resulted in increases in the quantum yield of cyclic electron flow (CEF) around PSI [Y(CEF)] while increasing the expression of antioxidant and AsA–GSH cycle-related genes and elevating the ratio of reduced glutathione/oxidized glutathione (GSH/GSSG). Similarly, AsA treatment significantly decreased the levels of reactive oxygen species [superoxide anion (O2−) and hydrogen peroxide (H2O2)] in these plants. Together, these data indicate that AsA can alleviate salt-stress-induced inhibition of PSII and PSI in tomato seedlings by restoring the excitation energy balance between the photosystems, regulating the dissipation of excess light energy by CEF and NPQ, increasing photosynthetic electron flux, and enhancing the scavenging of reactive oxygen species, thereby enabling plants to better tolerate salt stress.

Effects of exogenous ascorbic acid on photosynthesis and xanthophyll cycle in alfalfa (Medicago sativa L.) under drought and heat stress

“…The treatment of alfalfa leaves with exogenous AsA could mitigate the decrease in the photochemical activity of PSII, indicating that exogenous AsA can reduce the photoinhibition of alfalfa leaves under drought and heat stress. The application of AsA to reduce stress damage and its effects on the photosynthetic apparatus has been reported previously (Alayafi 2020, Chen et al 2023. Abiotic stress usually produces photoinhibition (Nawrocki et al 2021), and the protective effect of NPQ on the photosynthetic apparatus is closely related to excess energy dissipation in non-radiative processes (Yang et al 2011).…”