Activation-Tagged Tobacco Mutants that are Tolerant to Antimicrotubular Herbicides are Cross-Resistant to Chilling Stress

T-DNA activation tagging was used to generate tobacco mutants with increased tolerance to antimicrotubular herbicides and chilling stress. After transformation, protoplast-derived calli were screened for tolerance to treatments that affect microtubule assembly. In one screen mutants with tolerance to aryl carbamates (a blocker of microtubule assembly) were selected, the second screen was targeted to chilling-tolerant mutants that could survive for several months at 3°C, a third screen combined both factors. The resistance of these mutants to aryl carbamates or chilling was accompanied by resistance of microtubules to these factors. The carbamate tolerant mutants were cross-resistant to chilling stress. This was mirrored by an adaptive reorganization of microtubules and a reduction of microtubule dynamics in response to chilling. The analysis of these mutants suggests (1) that microtubule dynamics limit the tolerance to chilling and EPC, and (2) that the cold sensitivity of microtubules limits chilling tolerance in tobacco.