Chromate accumulation in Brassica juncea and Conyza canadensis grown under different sulfate availability

Plants of Brassica juncea (L.) Czern. and Conyza canadensis (L.) Cronq. were exposed at various sulfate/chromate concentration ratios for 2, 4 and 7d. After 7 d of exposure, higher sulfate uptake rates were observed in both plant species exposed to SO42- / CrO42- 1mM/0,2mM and to 1mM/ 1mM than in the control plants (SO42- 1mM). Throughout all the experimental period, no effects on sulfate uptake were observed in Brassica juncea plants grown at SO42-/CrO42- 0,2mM/ 0,2mM and 0,2mM/1 mM, while in Conyza canadensis plants a repression of the sulfate transport system was evidenced in plants exposed to SO42-/CrO42- 0,2mM/ 0,2mM and 0,2mM/ 1mM, with respect to control (SO42- 0,2mM). Accumulation of Cr in roots and shoots of both plant species was higher with external concentration of 1 mM chromate, independently on the sulfate availability. Brassica juncea plants accumulated Cr two-fold in roots and five-fold in shoots with respect to Conyza canadensis plants. In both plant species, a decrease in total biomass was observed after 4 d of chromate exposure.