The tomato mutant flacca wilts rapidly under water deficit because its stomata resist closure. Application of abscisic acid to intact mutant plants changes their morphology toward the phenotype of the control normal variety, Rheinlands Ruhm. The treated mutant plants do not show wilting symptoms, and the resistance to closure of their stomata decreases with hormone treatment.

Two of the major resistances to water flow which govern water status in the plant are the resistance to water absorption in the root and the resistance to water loss in the leaf (6,15). The effect of hormones on stomatal movement, which controls the flow of water vapor from the leaf, is well documented. While cytokinins (7,8,10) and possibly GA (7) induce opening of stomata, auxins (1, 9, 21) and ABA (11) cause them to close. Little is known, however, about hormonal effects on water absorption by the root. Indoleacetic acid treatment was found to increase root exudation in Pisum and Helianthus (14) and in tobacco (5), and 10-5 M GA increased it in tobacco (20). The rate of exudation was decreased, however, by 10-' M GA (20) in tobacco and by benzyladenine (18) in tomato.A study on the wilty mutant of tomato, flacca (flc), indicated that the irregularities of the water status in this plant may be explained by the hormonal changes demonstrated in the plant (2,17,18). The tomato mutant wilts faster than the normal variety Rheinlands Ruhm (RR), used as control, because its stomata resist closure (16). This persistence of open stomata, which results in a higher rate of transpiration than in the normal plant, was explained by the higher kinetin-like activity (18) and the lower concentration of ABA-like substances (17) in fic compared with RR. In agreement with this suggestion was the simultaneous decrease with age of stomatal resistance to closure and kinetin-like activity and the increase with age of ABA-and auxin-like activity (17,18).In contrast with the higher rate of transpiration, the amount of exudate per unit root dry weight from 5-week-old mutant plants was only 0.35 that of the normal plant (18). The osmotic pressure of the mutant sap, however, was about twice as high as that of the normal plant. The rate of exudation was lower also in mutant plants enclosed in plastic bags for 12 hr prior to decapitation to prevent transpiration. This fact suggests that the lower amount and the higher osmotic pressure of root exudate in the mutant do not result from the higher transpiration of that plant. In the older plants, however, the exudation of the two genotypes, mutant and normal, was nearly the same (18). The closer agreement with age between the amount of exudation in the mutant and that of the normal plant suggests that root resistance, like stomatal behavior, depends on the specific hormonal status in the mutant.This suggestion was tested by examining the effect of cytokinins, ABA, and natural and synthetic auxins on bleeding of wounds left after removal of the upper leaves, and on the amount and osmotic presure of root exudate in mutant and normal plants.Mutant and normal plants were grown in half-concentration Hoagland solution in 1-liter plastic bottles up to the 9 to 10 leaf stage. They were then treated with the hormone solutions. Plants which were sprayed seven times a day for 2 days with ABA or 2,4-D (10 mg/liter) exhibited strong bleeding compared with the control. There was no bleeding at all in either...

The wilty tomato mutant, flacca, and the normal variety, Rheinlands Ruhm, were compared for kinetin-like activity in ontogeny. The mutant wilts easily because its stomata resist closure. This stomatal resistance decreases with age. The occurrence of a root factor which induces stomatal opening was inferred from grafting experiments. It was hypothesized that the excessive stomatal openings in thc mutant may result from excess of kinetin -like activity in the leaf of that plant. In addition, it was suggested that the closure of stomata in the aging mutant is due to a decrease of kinetin-like activity with age. Kinetin-like activity in the leaf was determined by incorporation of labeled leucine. The concentration of cytokinins in root exudate and leaf extract was determined by the sovbean callus assay. Evidence was presented of higher kinetin-like activity in the leaves of the mutant and higher cytokinin concentration in its root exudate. Cytokinin concentration in the shoot was found to be only slightly higher in the mutant than in the normal plants. Kinetin-like The following working hypothesis is suggested to explain the excessive stomatal opening and the root effect in the mutant. The excessive opening of stomata is induced by a higher kinetinlike activity occurring in the mutant leaf, compared with the normal. This higher activity in the mutant leaf may result either from a higher concentration of cytokinins produced by the mutant root, or from a lower concentration of antagonists to cytokinins in the mutant leaf. The production of these inhibitory substances may depend on the root. The production of hormones with kinetin-like activity by the root has been demonstrated in several plant species (8,15,24). This paper presents a comparative study of kinetin-like activity in the leaf, concentration of kinetin-like substances in root exudate and shoot extract, and of stomatal behavior in young and mature mutant and normal plants. MATERIALS

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 leucineincorporation 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 auxinlike 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 auxinand abscisic acid-like activity and stomatal behavior.Stomatal mechanism is affected by the four groups of plant hormones, namely, kinins, auxins, possibly gibberellin, and abscisic acid. While kinetin and, apparently, gibberellic acid stimulate stomatal opening (7,8,10), auxins and abscisic acid induce closure (1,3,9, 19, 20 These authors also showed that abscisic acid inhibited most of the kinetin-stimulated transpiration.In the present series of studies, dealing with the hormonal imbalance in the wilty tomato mutant, flacca, an attempt has been made to correlate stomatal behavior with endogenous hormonal level. The wilting of theflacca mutant is caused by the abnormal behavior of its stomata. The mutant stomata resist closure in darkness as well as during water deficit (16). Tal et al. (18) suggested that excess kinetin-like activity was responsible for the excessive opening of the mutant stomata. The increased closing ability of the mutant stomata noted in older plants and leaves was explained by the decrease in kinetin-like activity. Tal (16) also indicated that some symptoms of auxin excess were evident in the mutant at maturity. These symptoms consisted of stem swelling and epinasty of branches and leaves, especially on the upper part of the plant. Other symptoms noted later were strong rooting along the stem, and delayed development of side shoots.Application of both the synthetic auxin, 2,4-D (17), and abscisic acid (5) caused stomatal closure in both normal and mutant plants...

The wilty tomato mutant Jfacca, the normal cultivar Lycopersicon escukntum Mill. Rheinlands Ruhm, and abscisic acid-induced phenotypic revertants were compared with respect to ethylene evolution, activity of tryptophan aminotransferase, and I1-"4Clindoleacetic acid decarboxylation. The modification of hormone balance in the wilty tomato mutantflcl is apparently responsible for the abnormalities of its stomatal behavior and morphology. This modification includes a reduced ABA level and an increase in the concentration of auxinlike substances and kinetin-like activity (13, 16). The reduced ABA level was suggested as the first of these three hormonal changes (7, 17) and seems to be the primary metabolic defect of this mutation.Following ABA treatment, the mutant completely reverts phenotypically to the normal type with regard to stomatal behavior (7), transpiration rate (7), root resistance to water flow (14), kinetin-like activity (16), as well as peroxidase (15) and RNase (9) activities. Similarly, the mutant morphological symptoms characteristic of excess of auxin activity (7), e.g. leaf epinasty, swelling of the upper stem, rooting along the stem, and pronounced apical dominance (12, 13), do not appear in ABA-treatedflc plants.Abeles (1) inhibition are mediated by ethylene production in many plant species. Auxin induces ethylene production, and ethylene in turn induces the morphological symptoms. Ethylene production is also known to be induced by water stress (3,4,8,22).In view of the knowledge reviewed above, we attempted to clarify in this work the following questions. (a) Does ABA affect auxin level through inhibition of IAA synthesis and/or enhancement of its breakdown? For this purpose, normal, mutant and ABA-treated mutant plants were compared with respect to the activity of Trp-aminotransferase, which is the first enzyme in the prevalent IAA biosynthetic pathway (10,19,21), and [I-14CJIAA decarboxylation, which is the first step in IAA breakdown. (b) Are the mutant morphological symptoms, characteristic of auxin excess, mediated by ethylene? Ethylene evolution was, therefore, compared in normal, mutant, and ABA-treated mutant plants, as it was assumed that if ethylene is a mediator hormone in auxin action, its production should be higher in the mutant than in the normal genotype. Accordingly, ethylene production was expected to decrease in ABA-treated mutant plants, in which the symptoms mentioned above do not appear. (c) Does ABA affect ethylene production through its effect on water balance? This aspect was studied by comparing ethylene evolution in normal and mutant plants grown under different humidities. Under normal greenhouse humidity (60-70%/o), mutant and normal plants differ in both ABA and water content (9,13,17