Abstract
Arabidopsis thaliana can enhance freezing tolerance (FT) by exposure to low, nonfreezing temperatures, a phenomenon known as cold acclimation (CA). CA is driven by expression of CBF/DREB1 but the mechanisms of the enhancement of FT are not fully understood. We herein screened for Arabidopsis mutants that remained FT during "cold deacclimation" (DA). An isolated mutant named freezing tolerant 1 (frt1) exhibited a greater degree of FT than the wild type, not only during DA but also under non-acclimated or CA conditions. RNA gel blot analysis demonstrated that the transcript levels of neither CBF/DREB1 nor its downstream COR genes were enhanced in the frt1 mutant over the wild type. The frt1 mutant accumulated slightly lower levels of proline than the wild type, but accumulated constitutively higher levels of sugars than the wild type, suggesting that enhanced FT of the frt1 mutant is due to its increased levels of sugars.
