THE STABILITY AND METABOLISM OF BENZYLADENINE GLUCOSIDES IN SOYBEAN CALLUS

Using cytokinin dependent soybean callus the 3-, 7- and 9-glucosides of BA were investigated with respect to biological activity and metabolic stability. [3G]BA was the most, and the [7G]BA the least active in the soybean callus bioassay. This order was also established with respect to the rates of metabolism, and is apparently the reason for 'the differential rates of cell division observed with the three BA-glucosides investigated. The rapid metabolism of [3G]BA resulted in the release of a biologically active compound that had a similar retention time to that of BA. As this hydrolysis and release of BA resulted in substantially better growth it provides further circumstantial evidence that the free base is the active cytokinin. Although all three glucosides have N-C bonds, [3G]BA is hydrolyzed more readily by acid. In addition it can be enzymatically hydrolyzed by beta-glucosidase. We propose that the term <<storage>> compound must be applied more rigorously with respect to cytokinin glucosides. In the case of [7G]BA and [9G]BA this term is clearly inappropriate and the terms <<detoxification, inactivation>> and/or <<bound>> seem more correct. As [3G]BA can be utilized readily and appears to serve as a ready source of BA (slow release compound) following application to plant tissues the use of the term <<storage>> compound appears in order. From the present results it would not seem as if there is reversible sequestration between BA and [3G]BA. During the 24 h of the experiment [7G]BA and [9G]BA but not [3G]BA were formed following BA application to soybean callus.