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 limitation and drought-induced gene expression, we have studied a model system consisting of a drought-tolerant line (pi) and a drought-sensitive line (S1) of sunflowers (Helianthus annuus L.) subjected to progressive drought. pi tolerance is characterized by the maintenance of shoot 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 leaf water status in R1 and S1 plants during progressive drought. In leaves of pi plants the accumulation of HaDhn1 and HaDhn2 transcripts, but not HaElip1 transcripts, was correlated with the drought-adaptive response. Drought-induced abscisic acid (ABA) concentration was not associated with the varietal difference in drought tolerance. Stomata of both lines displayed similar sensitivity to ABA. ABA-induced accumulation of HaDhn2 transcripts was higher in the tolerant than in the sensitive genotype. HaDhn1 transcripts were similarly accumulated in the tolerant and in the sensitive plants in response to ABA, suggesting that additional factors involved in drought regulation of HaDhn1 expression might exist in tolerant plants.