Sensitivity of oat leaf chlorophyll retention bioassay to natural and synthetic cytokinins

The cytokinin bioassay based on retention of chlorophyll in excised oat leaf pieces is more sensitive to the synthetic cytokinins (6-benzylaminopurine and kinetin) than to the natural cytokinins (trans-zeatin and N 6 -[Δ 2 isopentenyl]adenine). This difference in sensitivity decreases with increasing length of leaf pieces (from 2 to 10 cm) and with increasing volume of application (from 5 μ1 to 25 μl). Application of the cytokinin solution to the basal and apical part of the 8 cm pieces decreases the sensitivity of the bioassay but has no significant effect on the relative activities of trans-zeatin and 6-benzylaminopurine. Using 7 cm pieces and 20 μl of solution the trans-zeatin and N 6 -(Δ 2 -isopentenyl)-adenine can be detected at concentrations of 10 -5 M and 5 x 10 -5 M, respectively.