Phytotoxic effects of hexavalent chromium on rapeseed plants

Rapeseed (Brassica napus L. subsp. napus) plants were exposed to six different concentrations (12, 24, 60, 120, 240, 480 μmol dm–3) of K2Cr2O7 for 7 days. Dry mass of shoots and roots decreased rapidly with increasing external Cr(VI) concentration. Application of Cr(VI) concentrations ³ 120 μmol dm–3 caused that leaves were strongly chlorotic and some of them even desiccated. Roots of these plants where subtile and brownish. Notable decrease in chlorophyll content was observed already at the lowest (12 μmol dm–3) used concentration. Content of soluble proteins in leaves decreased rapidly within the studied concentration range, whereby the lowest protein content was observed after application of 240 μmol dm–3 Cr(VI). Lipid peroxidation expressed as a content of malondialdehyde in leaves was notable already after application of 12 μmol dm–3 Cr(VI). At lower applied Cr(VI) concentrations (12÷120 μmol dm–3) the bioaccumulation factors related to Cr accumulation in roots were higher then those determined for shoots. Treatment with higher Cr(VI) concentrations (240 and 480 μmol dm–3) had an opposite effect and BAFs for the shoots exceeded those determined for the roots. The portion of Cr allocated in shoots related to the total Cr amount accumulated by plant ranged from 23.3% (12 μmol dm–3) to 94.7% (480 μmol dm–3). In the case of higher applied external Cr(VI) concentrations (120÷480 μmol dm–3) the defence mechanisms of plants were evidently impaired and uncontrolled Cr translocation within the plant occurred.