METABOLIC CHANGES ASSOCIATED WITH COLD-ACCLIMATION IN CONTRASTING CULTIVARS OF BARLEY

Cereal plants become more resistant to freezing when first exposed to a period of cold-acclimation. Many physiological and molecular changes have been shown to occur at low temperatures,but the role and the con tribution of each to frost resistance is still poorly understood. Two cultivars of barley (Hordeum vulgare L.), the winter barley Onice and the spring barley Gitane, were acclimated under controlled conditions under an 8-h photoperiod at 4 degrees C (light) and 2 degrees C (dark) for 21 days. Changes in free proline, ABA, water-soluble carbohydrate s and free fatty acids were measured to assess their involvement in co ld-acclimation and to explain the different frost-resistant capacities of the two cultivars. Exposure of barley plants to low temperature re sulted in an equal increase in proline in both cultivars. During the f irst days of cold acclimation, ABA levels showed a peak in the frost-r esistant cultivar, lasting about 24 h, followed by a decrease. The wat er soluble carbohydrates reached their highest content after 3 days of hardening, although after 14 to 21 days of acclimation the carbohydra te content was similar to that of unhardened plants. The frost-resista nt Onice had a much higher free fatty acid content than the frost-sens itive Gitane. Furthermore in Onice 86% of free fatty acids was represe nted by unsaturated molecular species, linolenic acid alone being 71%. In contrast, in the frost-sensitive cultivar only 31% of free fatty a cids was unsaturated and a large amount of 9-oxo-nonanoic acid, a prod uct present in the linolenic acid cascade, was also detected. The ABA content after 2 days of hardening and the free fatty acid composition were clearly different between the two cultivars and may explain, at l east in part, the different frost-resistant capacities of Onice and Gi tane.