Acquired tolerance to cadmium following long-term acclimation to CdCl2 in rice suspension cultures

Little is known concerning the long-term effects of cadmium (Cd) on plants. Here, rice (Oryza sativa L.) suspension cultures acquired tolerance to Cd toxicity after treated with 250 μM CdCl2 for 1 month, ensued with 300 μM CdCl2 for 18 months (acclimation). The tolerance was found associated with enhanced antioxidative capacity. The activities of superoxide dismutase, catalase and guaiacol peroxidase in acclimated cells were 1.58-, 3.16- and 11.24-fold respectively higher than that in non-acclimated cells when these cells were exposed to 300 μM CdCl2 for 4 days. Cd disturbed the homeostasis of ascorbate–dehydroascorbate (ASC–DHA) buffer system in the non-acclimated cells indicated by a sharp decrease in the ASC contents, whilst the ASC–DHA system was not affected in the acclimated cells. The acclimation also blocked the burst of hydrogen peroxide (H2O2) observed in the non-acclimated cells under Cd stress and conferred rice cells tolerance to H2O2 in vitro. To our knowledge, this is the first report of long-term effects of Cd on cell suspensions. This culture system may be further used to study the stress resistance breeding of crops.