Uptake, distribution and metabolism of 6-Benzyladenine and cytokinin content during callus initiation from actinidia deliciosa tissues

Abstract

6-benzyladenine (BA) uptake and metabolism, and cytokinin content were examined in Actinidia deliciosa petioles in relation to callus formation at the basal end of expiants. The samples were divided into apical, middle and basal portions after 1, 6, 12, 24, 48 and 96 h of exposure to 8-[14C]BA added to the callus induction medium. Initially, the petioles took up the BA actively, which remained as free-hormone in the tissues with the exception of a small portion that was transformed into nucleotide forms. From 12–24 h, the BA uptake decreased and the BA metabolism was triggered in the expiants, the 9-glycosylation being the main pathway of BA inactivation. The highest free BA levels in the tissue were reached at 24 and 48 h, coinciding with the induction period of cell division. Also at this time a high zeatin-type cytokinin amount was measured. The data suggest a direct relation between the cytokinin content in the expiants, mainly BA, and the induction and initiation of basal callus in kiwi petioles. The results do not show differences in cytokinin levels, which could explain the different proliferation ability of the petiolar portions: this fact could be associated with the maturation and differentiation state of the basal and apical cells.