Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: II. Auxin- and Abscisic Acid-like Activity.

The wilty tomato mutant, flacca, and the control variety, Rheinlands Ruhm, were compared with regard to the endogenous activity and concentration of auxin- and abscisic acid-like substances during ontogeny. The mutant wilts fast under water deficit because of inability to close its stomata. Symptoms characteristic of excessive auxin are evident in the developing mutant. Among these symptoms are branch and leaf epinasty, excessive rooting along the stem, and increased apical dominance. By using a leucine-incorporation assay, spray of whole plants with 2,4-dichlorophenoxyacetic acid, and wheat coleoptile bioassay, indications were found of an excess of activity and concentration of auxin-like substances in shoots of young and mature mutant plants. The wheat coleoptile bioassay also revealed a much lower amount of substances with abscisic acid-like activity in the mutant compared with the normal plant. In contrast to the appearance during ontogeny of morphological symptoms characteristic of auxin excess in the mutant, the absolute amount of auxin-like substances and their activity in incorporation of leucine decreased with age. A parallel decrease of the concentration and activity of auxin-like compounds was also found in the normal plant. The concentration of abscisic acid-like substances increased with age in both genotypes. The disagreement between the increasing morphological symptoms and the decrease of auxin-like activity and concentration is discussed, together with the possibility of a causal relationship between auxin-and abscisic acid-like activity and stomatal behavior.