Hormonal regulation of genetic tumor induction: Cytokinin and abscisic acid

Young seedlings of the tumor-prone amphiploid Nicotiana suaveolens × N. langsdorjfii were grown aseptically on nutrient medium in a controlled environment chamber. At regular intervals the incidence of tumor formation was scored and plants were harvested. Total cytokinin activity was determined by means of the cucumber cotyledon bioassay, while ABA activity was measured by radioimmunoassay. A close correlation between onset of tumor formation and elevation in endogenous cytokinin activity was demonstrated, but no correlation was observed between onset of tumorigenesis and change in the level of ABA. In addition, exposure of plants to exogenous ABA did not alter therate of tumor formation. These results are discussed in relation to the trigger mechanism for tumor induction in the Nicotiana system.