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 gro wth of w-1, a wilty, ABA-deficient sunflower (Helianthus annuus L.) mu tant, is described in comparison with the control line (W-1). Exogenou s ABA inhibited seed germination in both genotypes; however, for some ABA concentrations, whole achenes of w-1 mutant were slightly more inh ibited than the wild type; naked seeds of w-1 were significantly less inhibited than the wild type. To investigate the sensitivity to osmoti c stress in relation to ABA levels, naked seeds were subjected to diff erent PEG solutions. Mutant seeds showed a higher osmotic resistance, germinating at more negative osmotic potentials; moreover, at lo iv os motic 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 o f the w-1 genotype, but we cannot exclude the possibility that the wil ty mutant may have a complex alteration of either ABA synthesis and th e reception and/or transduction of the hormonal signal.