Cd²⁺ induced changes of ascorbate-glutathione cycle in Cd sensitive rice mutant cadB-1 leaves

【Objectives】 Cd2+ is easily absorbed from the soil by plants and accumulation in plants whichhealth threat to humans through human food chain. To investigate the mechanism of cadmium (Cd2+) induced oxidative stress and inhibit growth in a Cd sensitive rice mutant (cadB-1), a hydroponic experiment was conducted. 【Methods】 A japonica rice (Oryza sativa) variety Zhonghua 11 and the mutant rice seedlings obtained from the same rice variety as that formerly constructed with T-DNA/Ds insertion mediated by Agrobacterium.The transgenetic rice generations have stable hereditability and were used in this experiment.The seeds were surface sterilized in 0.5% sodium hypochlorite for 20 min, rinsed, and germinated in the dark on moistened filter paper at 30℃ for 2 d, and then moved to a plastic screen floating on distilled water at 28℃ for 4 d. Then uniformly germinated seedlings were transferred to black polyethylene barrels which contained 6 L of rice culture solution. Seedlings were grown in a growth chamber with a photo flux density of 500 μmol/(m2·s), relative humidity of approximately 65% and day/night temperatures of 32℃/27℃ (14 h/10 h). During the growth period, the solution was renewed every 5 d. At the seven leaf stage, rice seedlings include wild-type (WT) andcadB-1 exposed to 0.5 mmol/L CdCl2 for 0 (as control), 2, 4, 6, 8,or 12 d.【Results】 1) Cd and hydrogen peroxide (H2O2) accumulation were higher in cadB-1 than in wild one; 2) The ratios of reduced glutathione (GSH) and oxidized glutathione (GSSG), ascorbate (ASC) and dehydroascorbate (DHA), or reduced nicotinamide adenine dinucleotide phosphate (NADPH) and oxidized nicotinamide adenine dinucleotide phosphate (NADP+) were lower in cadB-1 than in WT; 3) Ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities were lower in cadB-1 than in WT in leaves during CdCl2 exposure periods.【Conclusion】 cadB-1 has lower level of antioxidants as well as lower activity of antioxidant enzymes. In addition, cadB-1 accumulates more Cd means that it can produce more reactive oxygen species (ROS). Videlicet, cadB-1 is deficient of the defense power against increased level of ROS which leads to a lower growth potential and sensitive to Cd.