Effect of stereospecific hydroxylation of N(6)-(Δ (2)-Isopentenyl)adenosine on cytokinin activity.

The cytokinin activities of cis and trans ribosylzeatin isomers and that of N(6)-(Δ(2)-isopentenyl)adenosine were compared in four bioassays. The trans isomer was found to be more active than the cis isomer in stimulation of cucumber cotyledon expansion (100x), retention of chlorophyll in detached leaf pieces (7x), induction and stimulation of chlorophyll synthesis in cucumber cotyledons (20x) and of betacyanin synthesis in Amaranthus caudatus seedlings grown in the dark (60x). The N(6)-(Δ(2)-isopentenyl)adenosine adenosine was less active than the trans ribosylzeatin in all four bioassays and more active than the cis ribosylzeatin in induction and stimulation of betacyanin and chlorophyll synthesis. These results show that the hydroxylation of the trans methyl group in the N(6) side chain of N(6)-(Δ(2)-isopentenyl)adenosine increases the biological activity and that this activity is either decreased or not significantly changed when the cis methyl group is hydroxylated.