Changes in gene expression in six alfalfa cultivars acclimated under winter hardening conditions

Alfalfa (Medicago sativa L.) improvement programs would benefit from the identification of gene products closely related to winterhardiness. The expression of cold-regulated (COR) genes was compared among six cultivars of contrasting winterhardiness by means of electrophoretic analysis of in vitro translation products. Plants were acclimated to simulated field conditions in an unheated greenhouse at a site near Quebec City during the 1992-1993 winter and were tested for their freezing tolerance and changes in gene expression. Down-regulated translation products cumulatively showed a stronger decline in the cold hardy cvs Rambler and Apica than in the non hardy cv Moapa 69. Conversely, up-regulated translation products progressively increased in the fall of 1992 and were cumulatively more abundant in hardy Rambler and Apica than in non hardy Moapa 69. A large degree of similarity occurred in the cold-induced changes observed for the six cultivars with noticeable differences between the classes of hardiness. A relationship was observed between the accumulation of specific translation products in a group of low molecular weight basic peptides (LMWBP) and the hardiness potential of the cultivars. In the LMWBP group, three peptides were present in the very hardy cultivars; a single peptide was observed in the moderately hardy cultivars; and none were detected in the non hardy cultivars. The single LMWBP present in hardy Apica was not induced by water stress and was absent in leaves. Differential accumulation of COR gene products in alfalfa cultivars of contrasting winterhardiness were documented. This study indicates that determination of hardiness potential in alfalfa might be related to the differential expression of a limited number of COR genes. Future characterization of gene products that preferentially accumulate in winterhardy cultivars will help elucidate the molecular bases of alfalfa adaptation to cold climates.