EFFECT OF THE PHYSICAL NATURE OF THE CULTURE-MEDIUM ON THE METABOLISM OF BENZYLADENINE AND ENDOGENOUS CYTOKININS IN ACTINIDIA-DELICIOSA TISSUES CULTURED IN-VITRO

Endogenous cytokinin and benzyladenine (BA) metabolites were studied in kiwifruit explants grown on solidified and liquid Murashige and Skoog media supplemented with BA. The same proliferation rate was observed in both media. However, in the liquid medium the release from apical dominance was faster and the growth rate was higher than on solid medium. At the same time the number of vitrified shoots increased considerably in the liquid cultures. Exogenous BA was transformed into 9-beta-D-glucopyranosyl-BA ([9G]BA), 7-beta-D-glucopyranosyl-BA ([7G]BA), 7-beta-D-ribofuranosyl-BA ([9R]BA) and the 5'-monophosphate of [BR]BA ([9R-5'P]BA). The proportion of active forms (BA, [9R-5'P]BA and [9R]BA) in respect to total BA metabolites, was generally higher in shoots from liquid than from solid media. An exception was found at day 20 when this balance was inverted. Endogenous cytokinins in kiwifruit shoots were measured by enzyme-linked immune sorbent assay (ELISA). The content of natural cytokinins was influenced by the levels of active forms of BA.