Abstract
In this study, the protective role of exogenous ascorbic acid (AsA) on salt-induced inhibition of photosynthesis in the seedlings of processing tomatoes under salt stress has been investigated. Plants under salt stress (NaCl, 100 mmol/L) were foliar-sprayed with AsA (0.5 mmol/L), lycorine (LYC, 0.25 mmol/L, an inhibitor of key AsA synthesis enzyme l-galactono-γ-lactone dehydrogenase activity), or AsA plus LYC. The effects of AsA on fast OJIP fluorescence rise curve and JIP parameters were then examined. Our results demonstrated that applying exogenous AsA significantly changed the composition of O-J-I-P fluorescence transients in plants subjected to salt stress both with and without LYC. An increase in basal fluorescence (Fo) and a decrease in maximum fluorescence (Fm) were observed. Lower K- and L-bands and higher I-band were detected on the OJIP transient curves compared, respectively, with salt-stressed plants with and without LYC. AsA application also significantly increased the values of normalized total complementary area (Sm), relative variable fluorescence intensity at the I-step (VI), absorbed light energy (ABS/CSm), excitation energy (TRo/CSm), and reduction energy entering the electron transfer chain beyond QA (ETo/CSm) per reaction centre (RC) and electron transport flux per active RC (ETo/RC), while decreasing some others like the approximated initial slope of the fluorescence transient (Mo), relative variable fluorescence intensity at the K-step (VK), average absorption (ABS/RC), trapping (TRo/RC), heat dissipation (DIo/RC) per active RC, and heat dissipation per active RC (DIo/CSm) in the presence or absence of LYC. These results suggested that exogenous AsA counteracted salt-induced photoinhibition mainly by modulating the endogenous AsA level and redox state in the chloroplast to promote chlorophyll synthesis and alleviate the damage of oxidative stress to photosynthetic apparatus. AsA can also raise the efficiency of light utilization as well as excitation energy dissipation within the photosystem II (PSII) antennae, thus increasing the stability of PSII and promoting the movement of electrons among PS1 and PSII in tomato seedling leaves subjected to salt stress.
Highlights
Xinjiang Province is one of the main producing regions of processing tomatoes in China
Because of excessive use of fertilizers, unreasonable methods of irrigation and drainage, and the special climatic conditions, the area is threatened by soil salinization, and soil secondary salinization has exceeded more than half of the total cultivated land dedicated to processing tomatoes
Our findings demonstrate that the exogenous application of ascorbic acid (AsA) can induce tomato seedling growth under salt-stress conditions, and it was associated with increases in endogenous AsA levels
Summary
Xinjiang Province is one of the main producing regions of processing tomatoes in China. Because of excessive use of fertilizers, unreasonable methods of irrigation and drainage, and the special climatic conditions (such as dryness due to less rain and strong evaporation in Xinjiang), the area is threatened by soil salinization, and soil secondary salinization has exceeded more than half of the total cultivated land dedicated to processing tomatoes. In recent years, this salinization problem became more and more serious, as it results in declines in photosynthetic rates, environmental resistance, and yield and quality of processing tomatoes. It is very important for plants to increase their salt tolerance and maintain their economic yield to counteract the adverse effects of salt stress on photosynthesis
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