Characterization of cadmium-tolerant carrot cells in response to cadmium stress

Non-tolerant (CW) and Cd-tolerant (CCd1) carrot (Daucus carota L.) cells we re compared for their response to cadmium (Cd). The CCd1 cells were induced by selection from the CW cells on a B5 medium containing 100 muM Cd. The C Cd1 cells were more tolerant to Cd than the CW cells. In an 80 muM Cd treat ment, the growth rate (8 d/0 d) based on the fresh weight of the CCd1 cells and CW cells was 69 and 24%, respectively, compared to the controls. Cd st ress led to the decrease of the total glutathione content and to the increa se of the contents of non-protein thiols (t-SH, phytochelatins) and Cd in b oth types of cells, Under Cd stress, the contents of t-SH and Cd of the CW cells were higher than those of the CCd1 cells. The CW cells in the 80 and 160 muM Cd treatments accumulated Cd with the increase in time. In contrast , the Cd content in the CCd1 cells in all the treatments and in the CW cell s in the 40 muM Cd treatment gradually decreased after 1 d. In an additiona l experiment, both types of cells pretreated with 20-80 muM Cd for id were transferred to a Cd-free medium, The CCd1 cells in all the pretreatments co ntinuously excluded Cd over a 4-d period, unlike the CW cells. Therefore, a larger depletion of Cd was found in the CCd1 cells, which maybe partially attributed to Cd tolerance.