Photosynthetic and antioxidant variability in soybean genotypes under Cadmium stress

Soyhean, the worldwide main source of oil and high protein feeds for the livestock sector has a high cadmium (Cd) accumulation capacity. With this background, the hydroponic culture experiments were conducted to investigate the effects of different concentrations of Cd (0-100 mu M) on growth, water relations, photosynthetic variables, oxidative stress, and antioxidant response in two soybean genotypes P-218 and P-898. Ten days old seedlings were subjected to (0-100 mu M CdCl2) for 15 days. The results indicated that the growth of genotype P-218 was not affected significantly upto 75 mu M CdCl2 treatment growth of P-828 was reduced significantly beyond 25,mu M.CdCl2 treatments. Cd toxicity caused severe impairments in photosynthetic variables like photosynthetic rate, chlorophyll fluorescence and chlorophyll content, in 898 than in P-218. The activities of antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) were higher in P-218 than in P-828 at various levels of Cd treatments. Chlorophyll fluorescence measurements revealed that non-photochemical quenching increased in P-218 and decreased in P-828 whereas the electron transport rate increased under Cd stress in P-828 and decreased in P-218. It is concluded that tolerance capacity of P-218 against Cd can be associated with the capability of this genotype in keeping an active photosynthetic system and strong antioxidant defense system.