Expression of antioxidant defense genes in mung bean (Vigna radiata L.) roots under water-logging is associated with hypoxia tolerance

This study was conducted to examine the extent of oxidative stress and the role of antioxidant enzymes on hypoxia tolerance in highly tolerant wild species Vigna luteola, and mung bean (Vigna radiata) cvs. T 44 (tolerant) and Pusa Baisakhi (susceptible). Two days of water-logging caused about 40-50% decline in superoxide radical (O-2 (center dot-)) and hydrogen peroxide (H2O2) contents in all the genotypes, however, further water-logging to 8 days caused significant increase in O-2 (center dot-) and H2O2 contents, and the values were 80-90% of the control values. In control and revived plants O-2 (center dot-) and H2O2 contents were higher in Pusa Baisakhi, while under water-logging stress T 44 and V. luteola showed greater increases in the O-2 (center dot-) and H2O2 contents. Hypoxia induced increase in superoxide dismutase, ascorbate peroxidase, and glutathione reductase activities were higher in T 44 and V. luteola compared with Pusa Baisakhi; and the increases in T 44 and V. luteola continued up to 8th day of water-logging, while in case of Pusa Baisakhi, the maximum increase was observed only on the 2nd day of water-logging. Gene expression studies showed enhanced expression of cytosolic-Cu/Zn-superoxide dismutase (SOD) and cytosolic-ascorbate peroxidase (APX) in the roots of waterlogged V. luteola and T 44, while little expression was observed in control or treated plants of Pusa Baisakhi. PCR band products were cloned and sequenced, and partial cDNAs of Cu/Zn-SOD and APX, respectively, were obtained. Results suggest that increase in the activity of antioxidant enzymes is to scavenge reactive oxygen species produced both during and after relief from water-logging stress.