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 mu M CdCl2 for 1 month, ensued with 300 mu M 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 mu M 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.