Toxicity of arsenate and arsenite on germination, seedling growth and amylolytic activity of wheat

Effects of different concentrations of arsenite and arsenate (0-16 mg/l) on seed germination, relative root length and shoot height, arsenic accumulation in young seedlings, alpha-amylase, beta-amylase and total amylolytic activity in wheat were investigated in order to elucidate the toxicity of arsenic in the early developmental stage. Germination percentages of different wheat varieties had different responses to arsenic species and decreased significantly with increasing arsenic concentrations except Duokang 1. Relative root length (RRL) and relative shoot height (RSH) of wheat seedlings decreased with increasing concentrations of arsenite and arsenate. The relative root lengths were correlated with the relative shoot heights for arsenite (r(2)=0.79) and arsenate (r(2)=0.77). Arsenic uptake by seedlings increased with the increasing concentrations of arsenite or arsenate and followed the Michaelis-Menten kinetics function. The average total amylolytic activity and P-amylase activity had no significant difference comparable to that of controls at the concentration <= 2 mg/l arsenite or arsenate, but decreased apparently when the concentration was higher than 2 mg/l. Whereas the a-amylase activity decreased with increasing concentrations of arsenite or arsenate over the whole concentration range. Arsenite decreased all the endpoints more remarkably than arsenate. In comparison, shoot height and root length were more sensitive to arsenic than other endpoints and might be used as indicators for arsenic toxicity. (C) 2005 Elsevier Ltd. All rights reserved.