Nitric oxide production and scavenging in waterlogged roots of rape seedlings

When plant roots are waterlogged, plants can experience hypoxic stress. Large quantities of nitric oxide (NO) can be generated under hypoxic conditions as a result of nitrate reduction. Our objective was to investigate the molecular mechanisms behind NO production and scavenging (turnover) in waterlogged roots of rape ('Tammi' variety) seedlings by surveying waterlogging-responsive genes. Waterlogging for up to 72 h enhanced NO production rapidly in the roots. Of 53,107 genes assayed, 9,692 showed a twofold change in expression within 36 h of waterlogging. Two nitrate reductase (NaR) genes (TC201891, TC161540) and four nitrite reductase (NiR) genes (TC168889, TC164215, TC163914, TC185634) were potentially involved in NO production in response to waterlogging stress. Strong hypoxic induction of non-symbiotic hemoglobin (Hb) gene (TC165566), which increased 656- and 645-fold at 36 and 72 h of waterlogging, respectively, could oxidize the NO overproduced in the roots. Our results suggested that reduction of nitrate to NO by NaR and NiR and subsequent NO turnover by Hb provide a mechanism for maintaining bioenergetics in waterlogged roots. The up-regulation of many additional waterlogging-responsive genes with potential roles in the anaerobic respiration, sucrose and starch degradation, glycolysis, and pyruvate metabolism, may acclimate the plant to waterlogging-induced hypoxic condition.