CHANGES IN GENE-EXPRESSION IN 6 ALFALFA CULTIVARS ACCLIMATED UNDER WINTER HARDENING CONDITIONS

Alfalfa (Medicago sativa L.) improvement programs would benefit from t he identification of gene products closely related to winterhardiness. The expression of cold-regulated (COR) genes was compared among six c ultivars of contrasting winterhardiness by means of electrophoretic an alysis of in vitro translation products. Plants were acclimated to sim ulated field conditions in an unheated greenhouse at a site near Quebe c City during the 1992-1993 winter and were tested for their freezing tolerance and changes in gene expression. Down-regulated translation p roducts cumulatively showed a stronger decline in the cold hardy cvs R ambler and Apica than in the non hardy cv Moapa 69. Conversely, up-reg ulated translation products progressively increased in the fall of 199 2 and were cumulatively more abundant in hardy Rambler and Apica than in non hardy Moapa 69. A large degree of similarity occurred in the co ld-induced changes observed for the six cultivars with noticeable diff erences between the classes of hardiness. A relationship was observed between the accumulation of specific translation products in a group o f low molecular weight basic peptides (LMWBP) and the hardiness potent ial of the cultivars. In the LMWBP group, three peptides were present in the very hardy cultivars; a single peptide was observed in the mode rately hardy cultivars; and none were detected in the non hardy cultiv ars. 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 doc umented. This study indicates that determination of hardiness potentia l in alfalfa might be related to the differential expression of a limi ted number of COR genes. Future characterization of gene products that preferentially accumulate in winterhardy cultivars will help elucidat e the molecular bases of alfalfa adaptation to cold climates.