title: Arabidopsis thaliana avoids freezing by supercooling.
abstract: 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.
authors.affiliation: Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
authors.forename: Marjorie
authors.initials: M
authors.lastname: Reyes-Díaz
authors.forename: Nancy
authors.initials: N
authors.lastname: Ulloa
authors.forename: Alejandra
authors.initials: A
authors.lastname: Zúñiga-Feest
authors.forename: Ana
authors.initials: A
authors.lastname: Gutiérrez
authors.forename: Manuel
authors.initials: M
authors.lastname: Gidekel
authors.forename: Miren
authors.initials: M
authors.lastname: Alberdi
authors.forename: Luis J
authors.initials: LJ
authors.lastname: Corcuera
authors.forename: León A
authors.initials: LA
authors.lastname: Bravo
mesh_terms: D000064:Acclimatization; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D050260:Carbohydrate Metabolism; D003080:Cold Temperature; D005615:Freezing; D005838:Genotype; D007053:Ice; D009154:Mutation; D010788:Photosynthesis / Q000502:physiology; D010860:Pigments, Biological / Q000032:analysis; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D007053:Ice; D010860:Pigments, Biological