Background and aims: Most physiological and biochemical studies on salt stress are NaCl-based. However, other ions (e.g., K+, Ca2+, Mg2+, and SO42−) also contribute to salt stress in special circumstances. In this study, salt stress induced by various salts was investigated for a better understanding of salinity.
Methods: Arabidopsis thaliana plants were stepwise acclimated to five iso-osmotic salts as follows: NaCl, KCl, Na2SO4, K2SO4, and CaCl2.
Results and Conclusions: Exposure to KCl and K2SO4 led to more severe toxicity symptoms, smaller biomass, and lower level of chlorophyll than exposure to NaCl and Na2SO4, indicating that Arabidopsis plants are more sensitive to potassium salts. The strongly reduced growth was negatively correlated with the accumulation of soluble sugars observed in KCl- and K2SO4-treated plants, suggesting a blockage in the utilization of sugars for growth. We found that exposure to KCl and K2SO4 suppressed or even blocked sucrose degradation, thus leading to strong accumulation of sucrose in shoots, which then probably inhibited photosynthesis via feedback inhibition. Moreover, K+ was more accumulated in shoots than Na+ after corresponding potassium or sodium salt treatments, thus resulting in decreased Ca2+ and Mg2+ concentrations in response to KCl and K2SO4. However, K2SO4 caused more severe toxicity symptoms than iso-osmotic KCl, even when the K+ level was lower in K2SO4-treated plants. We found that Na2SO4 and K2SO4 induced strong accumulation of tricarboxylic acid intermediates, especially fumarate and succinate which might induce oxidative stress. Thus, the severe toxicity symptoms found in K2SO4-treated plants were also attributed to SO42− in addition to the massive accumulation of K+.
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