Cytokinin oxidase/dehydrogenase activity as a tool in gibberellic acid/cytokinin cross talk

Changes in endogenous cytokinin (CK) content and cytokinin oxidase/dehydrogenase activity (CKX) in response to gibberellic acid (GA3) in two pea cultivars with different life span were assessed. The control leaves of cv. Scinado, which developed faster, had higher initial cytokinin content and lower CKX activity, while opposite trend was observed in cv. Manuela with longer life span. Increased CKX and decreased CK content were detected in leaves of cv. Scinado after treatments with 0.5, 1 and 5 µM GA3. Changes in CK content and CKX activity in GA3-treated cv. Manuela leaves were reciprocal to those in cv. Scinado. CK content and CKX activity in roots were not significantly influenced by the application of GA3. The slight repression of CKX activity in some of the root samples was accompanied by increased isopentenyladenine and isopentenyladenine riboside content. Obtained results suggest that CKX was responsible for the changes in endogenous cytokinin pool in GA3-treated plants and most probably this enzyme represents an important link in GA/cytokinin cross talk.