Expression of a dehydrin gene during embryo development and drought stressin ABA-deficient mutants of sunflower (Helianthus annuus L.)

The synthesis of a particular class of proteins, the dehydrins, is a common response to drought in plants. Dehydrins are known to be synthesized by th e cell in response to abscisic acid, which represents a link between enviro nment and nuclear activity, though dehydrin genes may be expressed even con stitutively. We have investigated the relationship between abscisic acid (A BA) and accumulation of a dehydrin mRNA in sunflower, in which a dehydrin c DNA (HaDhn1a) was isolated. Tn particular, we studied changes in the steady -state level of dehydrin transcripts in two mutants for ABA synthesis and a ccumulation: nd-1 tan albino, non-dormant and lethal mutant with a very low ABA content and no ABA accumulation in response to stress) and w-1 (a wilt y mutant, with reduced ABA accumulation) during embryo and plantlet develop ment and drought stress. Differences between genotypes were observed throug h embryogenesis: w-1 shows a lower content of dehydrin transcripts in the e arly stages compared to control plants, indicating that ABA affects dehydri n mRNA accumulation; however, dehydrin transcripts level appears independen t of ABA content in late embryogenesis. Also during drought stress in w-1 a dult leaves, ABA is not quantitatively related to the steady-state level of the HaDhn1a transcripts. Finally, data on nd-1 mutant show a high level of dehydrin transcripts after drought stress in plantlet cotyledons and leafl ets. These results indicate the existence of two regulation pathways of HaD hn1a transcripts accumulation, an ABA-dependent and an ABA-independent one, which may have cumulative effects.