ISOLATION OF MUTATIONS AFFECTING THE DEVELOPMENT OF FREEZING TOLERANCE IN ARABIDOPSIS-THALIANA (L) HEYNH

We screened for mutations deleterious to the freezing tolerance of Ara bidopsis thaliana (L.) Heynh. ecotype Columbia. Tolerance was assayed by the vigor and regrowth of intact plants after cold acclimation and freezing. From a chemically mutagenized population, we obtained 13 lin es of mutants with highly penetrant phenotypes. In 5 of these, freezin g sensitivity was attributable to chilling injury sustained during col d acclimation, but in the remaining 8 lines, the absence of injury pri or to freezing suggested that they were affected specifically in the d evelopment of freezing tolerance. In backcrosses, freezing sensitivity from each line segregated as a single nuclear mutation. Complementati on tests indicated that the 8 lines contained mutations in 7 different genes. The mutants' freezing sensitivity was also detectable in the l eakage of electrolytes from frozen leaves. However, 1 mutant line that displayed a strong phenotype at the whole-plant level showed a relati vely weak phenotype by the electrolyte leakage assay.