Response of cytokinin pool and cytokinin oxidase/dehydrogenase activity to abscisic acid exhibits organ specificity in peas

Changes in cytokinin pool and cytokinin oxidase/dehydrogenase activity (CKX EC: 1.5.99.12) in response to increasing abscisic acid (ABA) concentrations (0.5–10 μM) were assessed in the last fully expanded leaves and secondary roots of two pea ( Pisum sativum ) varieties with different vegetation periods. Certain organ diversity in CKX response to exogenous ABA was observed. Treatment provoked altered cytokinin pool in the aboveground parts of both studied cultivars. Specific CKX activity was influenced significantly basically in roots of the treated plants. Results suggest that ABA-mediated cytokinin pool changes are leaf-specific and involve certain root signals in which CKX activity presents an important link. This enzymatic activity most probably regulates vascular transport of active cytokinins from roots to shoots.