Seed germination and seedling growth in a wilty mutant of sunflower (Helianthus annuus L): Effect of abscisic acid and osmotic potential

The effect of abscisic acid (ABA) on seed germination and seedling growth of w-1, a wilty, ABA-deficient sunflower (Helianthus annuus L.) mutant, is described in comparison with the control line (W-1). Exogenous ABA inhibited seed germination in both genotypes; however, for some ABA concentrations, whole achenes of w-1 mutant were slightly more inhibited than the wild type; naked seeds of w-1 were significantly less inhibited than the wild type. To investigate the sensitivity to osmotic stress in relation to ABA levels, naked seeds were subjected to different PEG solutions. Mutant seeds showed a higher osmotic resistance, germinating at more negative osmotic potentials; moreover, at lo iv osmotic potentials, germination of w-1 seeds occurred much earlier than control seeds. Growth inhibition experiments indicated that shoot and root growth of m-1 seedlings is less sensitive to ABA with respect to control line. These differences may be related to the ABA deficiency of the w-1 genotype, but we cannot exclude the possibility that the wilty mutant may have a complex alteration of either ABA synthesis and the reception and/or transduction of the hormonal signal.