Cold‐Induced Biochemical and Molecular Changes in Alfalfa Populations Selectively Improved for Freezing Tolerance

Abstract

Synthetic populations obtained after successive cycles of recurrent selection for superior tolerance to freezing were used to probe the molecular bases of superior adaptation to cold in alfalfa {Medicago sativa L.). The initial genetic backgrounds and populations derived from the cultivars Apica and Evolution were assessed for their freezing tolerance and cold-induced molecular changes using plants acclimated to natural hardening conditions in an unheated greenhouse. Significant increase in freezing tolerance in response to recurrent selection was confirmed by the determination of the lethal temperature for 50% of the plants (LTjg). Improvement of freezing tolerance was associated with differences in cold-induced molecular changes. Starch reserves in crowns progressively declined during fall hardening with a more extensive mobilization observed in advanced cycles of selection. Concentrations of cryoprotective sugars and of the amino acids proline, asparagine, and arginlne increased during fall hardening and were significantly higher in recurrently selected populations than in the initial backgrounds. Transcript levels of two cold-regulated (COR) genes, cas15 and GaS, were strongly up-regulated during fall hardening and significantly increased in response to selection mostly in the Apica background. Our results provide evidence that recurrent selection for superior freezing tolerance in alfalfa induces marked changes in traits associated with the cold acclimation process.

Estimation of Rhizome Composition and Overwintering Ability in Perennial Sorghum spp. Using Near-Infrared Spectroscopy (NIRS)

“…Similar to fat, starch concentrations were negatively correlated with overwintering. This is in agreement with several previous studies [24,41,42]. Lower starch concentrations could reflect the breakdown of starch into sugars, which may be necessary for cold acclimation [25] and would be expected to decrease the freezing potential of the cells.…”

“…Higher concentrations of sucrose have been found in alfalfa (Medicago sativa L.) plants that were selected for their overwintering ability [24] and similar trends were reported in centipedegrass, Eremochloa ophiruoides (Munro) Hackel [28]. Hoffman et al [40] determined that the crowns of perennial ryegrass, Lolium perenne L., accumulated WSC when the temperature was as low as 2°C.…”

“…Additional assimilates associated with energy storage increase in response to environmental factors. For example, varying degrees of correlation between starch content and cold tolerance have been reported [24][25][26][27], and high concentrations of sucrose have been correlated with cold tolerance in several species [24,28]. The above findings indicate that predictive correlations between rhizome composition and overwintering ability may occur in Sorghum species.…”

Mapping Fall Dormancy and Winter Injury in Tetraploid Alfalfa

“…The well-known C-repeat binding factor (CBF) response pathway is involved in cold acclimation and freezing tolerance. The expression levels of these genes are related to freezing tolerance (Castonguay et al, 2011;Monroy et al, 1993). This activation initiates the expression cascade of cold-regulated (COR) genes, which further enhances a plant's ability to resist injury when exposed to freezing temperatures (Chinnusamy et al, 2007).…”

Reference Genes for RT-qPCR Analysis of Environmentally and Developmentally Regulated Gene Expression in Alfalfa

“…Plants of the initial cultivars ATF0 and ETF0 and populations ATF5 and ETF4 obtained after respectively five and four cycles of recurrent selection were grown under environmentally-controlled conditions and acclimated to natural hardening conditions in an unheated greenhouse as described in Castonguay et al [24]. Five pots (15 plants per pot) of each population were sampled before transfer the unheated greenhouse on October 15, 2003 and during the subsequent winter on January 21, 2004 after fall hardening.…”