JXB Advance Access originally published online on September 21, 2006
Journal of Experimental Botany 2006 57(14):3687-3696; doi:10.1093/jxb/erl125
RESEARCH PAPER |
Arabidopsis thaliana avoids freezing by supercooling
1Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile
2Departamento de Agroindustrias, Universidad de La Frontera, Temuco
3Instituto de Botánica, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile
* To whom correspondence should be addressed. E-mail: lebravo{at}udec.cl
Arabidopsis thaliana (L.) Heynh. has been described as a freezing-tolerant species based on freezing-resistance assays. Nonetheless, this type of experiment does not discriminate between freezing-tolerance and freezing-avoidance mechanisms. The purpose of this paper was to determine which of these two freezing-resistance mechanisms is responsible for freezing resistance in A. thaliana. This was achieved by comparing the thermal properties (ice-nucleation temperature and the freezing temperature) of leaves and the lethal temperature to 10, 50 and 90% of the plants (LT10, LT50, and LT90, respectively). Two wild-type genotypes were used (Columbia and Ler) and their mutants (esk-1 and frs-1, respectively), which differ in their freezing resistance. This study's results indicated that the mutant esk-1, described as a freezing-tolerant species showed freezing tolerance only after a cold-acclimation period. The mutant frs-1, described as freezing sensitive, presented freezing avoidance. Both wild genotypes presented LT50 similar to or higher than the ice-nucleation temperature. Thus, the main freezing-resistance mechanism for A. thaliana is avoidance of freezing by supercooling. No injury of the photosynthetic apparatus was shown by measuring the maximal photochemical efficiency (Fv/Fm) and pigments (chlorophyll and carotenoid) during cold acclimation in all genotypes. During cold acclimation, Columbia and esk-1 increased total soluble carbohydrates in leaves. esk-1 was the only genotype that presented freezing tolerance after cold acclimation. This feature could be related to an increase in sugar accumulation in the apoplast.
Key words: Apoplastic fluid, Arabidopsis thaliana, chlorophyll fluorescence, cold acclimation, esk-1, freezing avoidance, freezing tolerance, frs-1, sucrose, supercooling, total soluble sugars