Nitrate reductase-mediated nitric oxide production alleviates Al-induced inhibition of root elongation by regulating the ascorbate-glutathione cycle in soybean roots

Although the studies on nitric oxide (NO) in Al toxicity has been reported, the results are controversial. The aim of this study is to investigate the role of NO in Al-induced root growth inhibition in soybean (Glycine max L.). NO donor and scavenger were used to test the effects of NO on root elongation, lipid peroxidation, reactive oxygen species (ROS) accumulation, and ascorbate-glutathione cycle (AsA-GSH) under Al stress. Application of butylated hydroxyanisole, a lipophilic antioxidant, reduced Al-induced lipid peroxidation and root inhibition. NO donor alleviated Al-induced root inhibition and ROS accumulation as well as lipid peroxidation, while NO scavenger aggravated the observed effects of Al. In addition, NO accumulation in root apexes under Al stress was mediated by nitrate reductase (NR). Furthermore, the levels of GSH and AsA were enhanced by Al and further elevated by NO donor, but suppressed by NO scavenger. Moreover, the activities of key enzymes in AsA-GSH cycle were positively regulated by NO under Al stress. These results indicate that NR-mediated NO improves Al-induced root growth inhibition, possibly through its regulation of AsA-GSH cycle to maintain high levels of AsA and GSH, subsequently reducing ROS accumulation and thus alleviating lipid peroxidation.