CHARACTERIZATION OF A WILTY SUNFLOWER (HELIANTHUS-ANNUUS L) MUTANT .3. PHENOTYPIC INTERACTION IN RECIPROCAL GRAFTS FROM WILTY MUTANT AND WILD-TYPE PLANTS

The present study was conducted to evaluate phenotypic interaction in reciprocal grafts between wilty (w-1) sunflower mutant and normal (W-1 ) plants. The w-1 genotype is a 'leaky' ABA-deficient mutant, characte rized by high stomatal conductance, in both light and dark conditions, and high transpiration rate, In well-watered conditions, mutant scion s grafted on to normal rootstock (w-1/W-1) showed higher leaf relative water content, leaf water potential and ABA levels than those of cont rol grafts (w-1/w-1), in addition, detached leaves of w-1/W-1 exhibite d lower water loss than w-1/w-1 grafts, while mutant rootstock did not affect the transpiration rate of detached W-1 leaves. When drought st ress was imposed to potted plants by withholding water, the mutant sci ons grafted on to normal roots showed a partial phenotypic reversion. A rapid stomatal closure and a rise in ABA levels in response to a sma ll decrease in leaf water potential was observed. By contrast, in w-1/ w-1 grafts significant reductions in stomatal conductance and ABA accu mulation were detected only in conjunction with a severe water deficit , W-1 scions on mutant stocks (W-1/w-1) maintained the normal phenotyp e of control wild-type grafts (W1/W-1),