We analyzed changes in populations of translatable mRNAs occurring in crowns of the cold-tolerant alfalfa ( Medicago sativa L.) cv. Apica (CT) and the cold-sensitive cv. CUF-101 (CS) after their acclimation at low nonfreezing temperatures and at subzero temperatures. Both cultivars showed very similar translation profiles under all treatments. Low temperatures induced significant changes in the populations of translatable mRNAs. We observed a relationship between the accumulation of cold-regulated (COR) translation products and freezing tolerance within cultivars. Moreover, at least three COR translation products were specific to the CT and might be related to hardiness potential in alfalfa. Whereas extension of the cold acclimation period at 2�C reduced cold tolerance, incubation at subzero temperatures increased or maintained freezing tolerance. This increased hardiness was associated with enhanced translation of COR polypeptides and also with the appearance of new translatable mRNAs. This is, to our knowledge, the first report of altered gene expression in plants incubated at subzero temperatures. Marked changes in populations of translatable mRNAs at temperatures below freezing might be related to previous reports that alfalfa achieves maximum hardiness under snow cover when the soil has frozen. Translation in the presence of [3H]glycine showed that a large proportion of the COR genes encode for glycine-rich proteins (GRPs) and that some of the GRPs are specific to the CT.
Copyright (C) 1993, The Japanese Society of Plant Physiologists
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