Enhanced root hydraulic conductance by aquaporin regulation accounts for silicon alleviated salt-induced osmotic stress in Sorghum bicolor L

Abstract

It has been widely reported that silicon (Si) improves the resistance of plants to salt stress. Most of the previous studies have examined how silicon prevents Na+ uptake, but the performance and underlying mechanism through which silicon alleviates salt-induced osmotic stress has been largely ignored. In the present study, the mechanism through which Si alleviates salt-induced osmotic stress was investigated using sorghum in a hydroponic system. Si had no effect on seedling growth under normal conditions. Under salt stress, the photosynthesis and transpiration rate were decreased, but these decreases were alleviated by Si application. In addition, the leaf water content and leaf elongation rate were maintained at higher levels with Si than without Si. The root hydraulic conductance (Lp) of the seedlings were inhibited by salt, but Si application alleviated this inhibition. Under salt stress, the transpiration rates of the seedlings both with and without Si were decreased to the same level by HgCl2 treatment and partially rescued by β-mercaptoethanol treatment, suggesting that aquaporin was responsible for the alleviation of the decrease in Lp. Moreover, transcript levels of several aquaporin genes were upregulated by Si. Under salt stress, Si inhibited the increase in the root H2O2 levels and enhanced the activities of antioxidant enzymes. Moreover, similar to Si, pre-treatment with catalase alleviated the decrease in the transpiration rate, indicating that Si enhanced aquaporin activity by reducing H2O2 accumulation. These results indicate that under short-term salt stress, Si application can alleviate the decrease in Lp by mediating aquaporin activity, leading to increased water uptake and resistance to salt-induced osmotic stress.