Cadmium tolerance in tobacco cell culture and its relevance to temperature stress.

Growth of unselected tobacco (Nicotiana tabacum W38) cell suspension cultures was reduced by 50-200 μM cadmium (Cd) in the culture medium and cells were killed by 400 μM Cd. Tolerance to Cd was increased either by using rapidly growing cells or by culturing cells at higher densities. Cell lines tolerant to 2 mM Cd were established by progressively elevating levels of Cd in the culture medium. The Cd tolerance was not due to differences in uptake between unselected and Cd-tolerant cell lines, and the tolerance to Cd was not lost during long term culture in the absence of Cd. Cd-tolerant cells also showed higher tolerance to heat shock (37.5°C, 2-8 hours) and cold treatments (4°C, 1-7 days) than the unselected cells.