Nitric oxide enhances aluminum tolerance by affecting cell wall polysaccharides in rice roots

Nitric oxide (NO) is a key signal molecule involved in many physiological processes in plants. To study the mechanisms of exogenous NO contribution to alleviate the aluminum (Al) toxicity, roots of rice (Oryza sativa) seedlings pre-treated with sodium nitroprusside (SNP, a NO donor) were used to investigate the effect of Al in this study. Results indicated that NO alleviated the lipid peroxidation induced by Al and promoted the root elongation, whereas butylated hydroxyanisole (BHA), an efficient lipophilic antioxidant, alleviated the lipid peroxidation only. Rice seedling roots pre-treated with SNP followed by Al treatment had lower contents of pectin and hemicellulose, lower Al accumulation in root tips and cell walls, higher degree of methylation of pectin and lower wall Al-binding capacity than the roots with Al treatment only. Therefore, the decreased Al accumulation in the cell walls of rice roots is likely to be the reason for the NO-induced increase of Al tolerance in rice, and it seems that exogenous NO enhanced Al tolerance in rice roots by decreasing the contents of pectin and hemicellulose, increasing the degree of methylation of pectin, and decreasing Al accumulation in root cell walls.