Activation-tagged tobacco mutants that are tolerant to antimicrotubular herbicides are cross-resistant to chilling stress

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 3degreesC, 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.