Gas Exchange, Stomatal Behavior, and δ13C Values of the flacca Tomato Mutant in Relation to Abscisic Acid

The relationship between stomatal conductance and capacity for assimilation was investigated in flacca, a mutant of tomato (Lycopersicon esculentum Mill.) that has abnormal stomatal behavior and low abscisic acid (ABA) content. The assimilation capacity, determined by measuring assimilation rate as a function of intercellular CO(2) pressure, did not differ in leaves of flacca and its parent variety, Rheinlands Ruhm (RR). On the other hand, stomatal conductance of flacca leaves was greater than that of RR, and could be phenotypically reverted by spraying with 30 micromolar ABA. Stomatal conductance of flacca leaves was also reduced by increasing CO(2) pressure, increasing leaf to air vapor pressure difference, and decreasing quantum flux, irrespective of ABA treatment.The high conductance of flacca leaves resulted in a high intercellular CO(2) pressure. This allowed greater discrimination against (13)CO(2), as evidenced by more negative delta (13)C values for flacca as compared to RR. The delta (13)C values of both flacca and RR plants as influenced by ABA treatment were consistent with predictions based on gas exchange measurements, using a recent model of discrimination.