MOLECULAR AND PHYSIOLOGICAL-RESPONSES TO WATER-DEFICIT IN DROUGHT-TOLERANT AND DROUGHT-SENSITIVE LINES OF SUNFLOWER - ACCUMULATION OF DEHYDRIN TRANSCRIPTS CORRELATES WITH TOLERANCE

To investigate correlations between phenotypic adaptation to water lim itation and drought-induced gene expression, we have studied a model s ystem consisting of a drought-tolerant line (pi) and a drought-sensiti ve line (S1) of sunflowers (Helianthus annuus L.) subjected to progres sive drought. pi tolerance is characterized by the maintenance of shoo t cellular turgor. Drought-induced genes (HaElip1, HaDhn1, and HaDhn2) were previously identified in the tolerant line. The accumulation of the corresponding transcripts was compared as a function of soil and l eaf water status in R1 and S1 plants during progressive drought. In le aves of pi plants the accumulation of HaDhn1 and HaDhn2 transcripts, b ut not HaElip1 transcripts, was correlated with the drought-adaptive r esponse. Drought-induced abscisic acid (ABA) concentration was not ass ociated with the varietal difference in drought tolerance. Stomata of both lines displayed similar sensitivity to ABA. ABA-induced accumulat ion of HaDhn2 transcripts was higher in the tolerant than in the sensi tive genotype. HaDhn1 transcripts were similarly accumulated in the to lerant and in the sensitive plants in response to ABA, suggesting that additional factors involved in drought regulation of HaDhn1 expressio n might exist in tolerant plants.