Combined toxicity of cadmium and arsenate to wheat seedlings and plant uptake and antioxidative enzyme responses to cadmium and arsenate co-contamination.

To demonstrate the combined toxicity of cadmium (Cd) and arsenate (As) to early developmental stages of six wheat varieties, young seedlings were exposed to solutions containing both contaminants and seed germination frequency and seedling biomass, root length and shoot height, Cd and As uptake, amylase activity, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), soluble protein and malondialdehyde (MDA) concentrations in the seedlings were investigated. Seed germination and seedling biomass and root and shoot elongation decreased significantly (P<0.01) with increasing concentrations of Cd and As and root length appeared to be the most sensitive parameter. Uptake of Cd and As by seedlings increased with increasing Cd and As concentrations in the test solutions and obeyed Michaelis-Menten kinetics. Average total amylolytic, alpha-amylase and beta-amylase activities seemed to decrease with Cd concentrations >4mgL(-1) and As > or = 4mgL(-1). Seedling contents of soluble protein, MDA and POD increased and the activities of SOD and CAT decreased with increasing concentrations of Cd and As following an initial increase. The MDA content was linearly and positively correlated with seed germination frequency, biomass increment, root length and shoot height elongation (P<0.01), suggesting that MDA may be useful as a biological indicator of Cd and As toxicity in wheat. Combined exposure to Cd and As produced greater toxicity to wheat than single exposure to each metal separately, and Cd and As in combination had an additive effect on seed germination frequency and antagonistic effects on seedling biomass and shoot and root elongation.