Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato

Abstract

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

Expression of the Arabidopsis Mutant abi1 Gene Alters Abscisic Acid Sensitivity, Stomatal Development, and Growth Morphology in Gray Poplars

“…This observation is in line with studies on ABA-deficient tomato and Arabidopsis mutants where low ABA levels coincided with elevated ethylene biosynthesis rates (Tal et al, 1979;Rakitina et al, 1994;Sharp et al, 2000;LeNoble et al, 2004). Interestingly, shoot growth is inhibited in these ABA-deficient herbaceous mutants, contrary to abi1 poplars where elevated ethylene biosynthesis correlated with enhanced shoot growth.…”

Interaction with ethylene: changing views on the role of abscisic acid in root and shoot growth responses to water stress

“…Consistent with the finding that ABA restricts ethylene production in waterstressed maize seedlings, it was reported that under wellwatered conditions, ethylene production was greater in shoots of the flacca (flc) mutant of tomato (Tal et al 1979) and in whole plants of the aba1 mutant of Arabidopsis (Rakitina et al 1994) than in the corresponding wild types. In flc, it was also shown that ethylene production could be reduced to normal levels with exogenous ABA.…”

“…Taylor (1987) reported that the inhibition of shoot growth in double mutants of flc, not and sit was partially alleviated when the plants were grown at high humidity, but information on plant water relations was not included so, again, full interpretation was not possible. In other studies in which flc was grown at high humidity, effects on growth were not reported (Puri & Tal 1977;Tal et al 1979).…”

Cuticle Biosynthesis in Tomato Leaves Is Developmentally Regulated by Abscisic Acid

“…Importantly, this allowed an assessment of conserved phenotypes in different genetic backgrounds. Most of the published analyses of ABA levels in the ABA-deficient not, sit, and flc tomato mutants have focused on their leaves (Tal, 1966;Tal et al, 1979;Nagel et al, 1994). We observed that this reduction in ABA levels was consistent throughout leaf development and in ripening fruits ( Fig.…”