Antioxidative defense system in pigeonpea roots under waterlogging stress

Pigeonpea [Cajanus cajan (L.) Millsp.] is a waterlogging-sensitive legume crop. We studied the effect of waterlogging stress on hydrogen peroxide (H2O2) content, lipid peroxidation and antioxidant enzyme activities in two pigeonpea genotypes viz., ICPL-84023 (waterlogging resistant) and MAL-18 (waterlogging susceptible). In a pot experiment, waterlogging stress was imposed for 6 days at early vegetative stage (20 days after sowing). Waterlogging treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) increased in pigeonpea roots as a consequence of waterlogged conditions, and all the enzyme activities were significantly higher in waterlogged ICPL-84023 than in MAL-18. POX activity was the maximum immediately after imposing stress, therefore, it was suggested to be involved in early scavenging of H2O2, while rest of the enzymes (CAT, APX, SOD and PPO) were more important in late responses to waterlogging. Present study revealed that H2O2 content is directly related to lipid peroxidation leading to oxidative damage during waterlogging in pigeonpea. Higher antioxidant potential in ICPL-84023 as evidenced by enhanced POX, CAT, APX, SOD and PPO activities increased capacity for reactive oxygen species (ROS) scavenging and indicated relationship between waterlogging resistance and antioxidant defense system in pigeonpea.