Silicon ameliorates manganese toxicity by regulating manganese transport and antioxidant reactions in rice (Oryza sativa L.)

This study aimed to investigate the roles of silicon (Si) in ameliorating manganese (Mn) toxicity in two rice (Oryza sativa L.) cultivars: i.e. cv. Xinxiangyou 640 (XXY), a Mn-sensitive cultivar and cv. Zhuliangyou 99 (ZLY), a Mn-tolerant cultivar. Plants were cultured in nutrient solution containing normal Mn (6.7 mu M) or high Mn (2.0 mM), both with or without Si supply at 1.5 mM Si. Plant growth was severely inhibited by high Mn in cv. XXY, but was enhanced by Si supply. In cv. XXY, Si-enhanced tolerance resulted from a restriction of Mn transport, whereas in cv. ZLY Mn uptake was depressed. In cv. XXY, high Mn significantly increased superoxide dismutase (SOD), catalase and ascorbate peroxidase activities but decreased non-protein thiols and glutathione concentrations, leading to accumulation of H2O2 and malondialdehyde. The addition of Si significantly counteracted high Mn-elevated malondialdehyde and H2O2 concentrations and enhanced plant growth. In cv. ZLY, high Mn considerably raised SOD activities and glutathione concentrations, thus leading to relatively low oxidative damage. Si-enhanced Mn tolerance was attributed mainly to restricted Mn transport in cv. XXY but to depressed Mn uptake in cv. ZLY. Silicon mainly influenced non-enzymatic antioxidants in these two rice cultivars under high Mn stress.