Effects of selenite and selenate on growth and physiological characteristics of pakchoi.

Pot experiments were conducted to study the effects of selenite and selenate on growth and physiological characteristics of the pakchoi and its physiological mechamism.The results showed that leaf length and width of pakchoi reduced significantly but DW biomass of pakchoi was not affected by selenite when added less than 10.0 mg·kg-1.Leaf length and width and DW biomass of pakchoi were not affected by selenate in the concentration of 1.0 mg·kg-1 treatment.At high selenium concentrations,leaf length and width and DW biomass of pakchoi reduced sharply with the increase of selenium concentration irrespective of selenite or selenate treatment.Chlorophyll content was not affected by selenium when selenite was added less than 40.0 mg·kg-1 or selenate less than 20.0 mg·kg-1,while chlorophyll formation was restrained with the increase of selenite and selenate concentration thereafter.At low selenium concentrations of selenite and selenate treatment,an increase in glutathione peroxidase(GSH-Px)activity and a decrease in lipid peroxidation products and MDA contents were observed.However,superoxide dismutase(SOD) activity,catalase(CAT) activity and proline contents were not affected at low selenium concentrations.At high concentrations,selenite and selenate enhancing the accumulation of MDA and proline,but GSH-Px activity decreased.Furthermore,CAT activity decreased but SOD activity increased at high selenium concentration.Peroxidase(POD) activity decreased irrespective of selenite or selenate added to the soil.The antioxidantive effects at low selenium concentration and pro-oxidantive effects at high selenium concentration of selenate were stronger than that of selenite.The bioavailablity and toxicity of selenate on pakchoi was bigger than that of selenite under current experimental conditions.