Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato: IV. Effect of Abscisic Acid and Water Content on RNase Activity and RNA.

Plants of the wilty tomato (Lycopersicum esculentum) mutant, flacca, and of the normal cultivar Rheinlands Ruhm 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 significantly. 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 plants 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, i.e. RNase activity.