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

Abstract

Plants of the wilty tomato (Lycopersicum esculentum) mutant,flacca, and of the normal cultivar Rheinlands Rubm growing under either "normal" or high humidity were used in this research. Under normal humidity, RNase activity was much higher in mutant plants in which abscisic acid (ABA) and water content were lower than in the normal plant. The mutant also contained less RNA and protein per cell and less soluble RNA relative to ribosomal RNA as compared with the normal genotype. In ABA-treated mutant plants, RNase activity decreased while RNA, protein, the ratio of soluble to ribosomal RNA and water content increased.Under high humidity, RNase activity in mutant plants was decreased, but was still somewhat higher than that in the normal plant, although water saturation deficit was equal in both plant types. Abscisic acid increased RNase activity in the mutant plants. The content of RNA and protein per cell was similar in both types, but the ratio of soluble to ribosomal RNA remained lower in the mutant. In ABA-treated mutant plants, although the content of DNA and RNA per fresh weight was similar to that of control mutant plants, the ratio of RNA to DNA decreased significandy. In addition, ABA caused an increase of the soluble to ribosomal RNA ratio toward the normal value in mutant plants.Contrary to ABA, kinetin increased RNase activity in the mutant under normal humidity and decreased it under high humidity.A similar incorporation of labeled uridine into RNA in normal, mutant, and ABA-treated mutant plants under normal humidity suggests that the difference between mutant and normal plats in respect to total, soluble, and ribosomal RNA results not from a different rate of RNA synthesis but from a different rate of RNA degradation, ie. RNase actvity.An increase of RNase activity (1,6,7,9,12,35) and a decrease of RNA level (8,12) was found in tomato and other plants subjected to water stress. The soluble fraction of RNA increased while the ribosomal fraction decreased in sugar beet under water stress (25). Low relative humidity appears to be associated with slow accumulation and reduced incorporation of labeled uracil into RNA in etiolated leaves of Jack bean (3).An association between RNase activity, RNA level, and hormone balance in the plant was also reported. Srivastava (29) found an increase of RNase activity in detached barley leaves treated with ABA and a decrease of this activity following treatment with kinetin. Similar hormonal effects on RNase activity were reported in other plants (5,13,28,39 The first attempt to elucidate the interrelations among RNase activity, water content, and hormone balance was made by Arad et al. (1). They found that in barley leaves, in which the water balance was not disturbed, ABA increased and kinetin decreased RNase activity. However, these hormonal effects were inverted in leaves subjected to water shortage i.e. ABA decreased and kinetin increased the activity. They interpreted these results to mean that above a certain optimal leaf water content, the specific ho...

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

“…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).…”