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

Non-tolerant (CW) and Cd-tolerant (CCdl) carrot (Daucus carota L.) cells were compared for their response to cadmium (Cd). The CCdl cells were induced by selection from the CW cells on a B5 medium containing 100 µM Cd. The CCdl cells were more tolerant to Cd than the CW cells. In an 80 µM Cd treatment, the growth rate (8 d/O d) based on the fresh weight of the CCdl cells and CW cells was 69 and 24%, respectively, compared to the controls. Cd stress led to the decrease of the total glutathione content and to the increase of the contents of non-protein thiols (t-SH, phytochelatins) and Cd in both types of cells. Under Cd stress, the contents of t-SH and Cd of the CW cells were higher than those of the CCdl cells. The CW cells in the 80 and 160 µM Cd treatments accumulated Cd with the increase in time. In contrast, the Cd content in the CCdl cells in all the treatments and in the CW cells in the 40 µM Cd treatment gradually decreased after 1 d. In an additional experiment, both types of cells pretreated with 20–80 µM Cd for 1 d were transferred to a Cd-free medium. The CCdl cells in all the pretreatments continuously excluded Cd over a 4-d period, unlike the CW cells. Therefore, a larger depletion of Cd was found in the CCdl cells, which may be partially attributed to Cd tolerance.