ABSCISIC-ACID AND PUTRESCINE ACCUMULATION IN CHILLING-TOLERANT RICE CULTIVARS

Rice (Oryza sativa L.) frequently confronts chilling injury at seedling stage when it is grown in early spring in temperate and subtropical areas. Understanding the physiological and genetic bases of chilling resistance should benefit our improvement of tolerance of rice seedlings to the stress. Previous study revealed that an accumulation of abscisic acid (ABA) or polyamines in rice seedlings responding to low temperature may be correlated with the chilling resistance of seedlings. The objective of this study, using rice seedlings with various genetic backgrounds, was to explore the relationships among the capacity of accumulation in ABA, putrescine, and chilling tolerance. Changes in ABA and putrescine levels in shoots and roots of seedlings after chilling treatment (5 degrees C) were measured and compared among 11 rice cultivars ranging from chilling-tolerant to sensitive. On exposure of seedlings to chilling, ABA and putrescine accumulated rapidly in both shoots and roots of chilling-tolerant cultivars. Changes in ABA levels were closely correlated with chilling tolerance of the tested cultivars (r = 0.96 in shoots and 0.92 in roots). Changes of putrescine levels in shoots were also positively correlated with the cultivar resistance to chilling (r = 0.95). Furthermore, among the tested cultivars, there was also a high correlation between the relative changes of ABA and putrescine in shoots. Our results suggest chilling-induced changes in ABA and putrescine levels may be used as physiological markers for chilling tolerance of rice seedlings.