The distribution of six eytokinins [zeatin, zeatin riboside, 6-(4hydroxy-3-methylbutylamino)purine, 6-(3-methylbut-2-enylamino)purine and its riboside, and kinetin] between aqueous buffers (pH 3.0 and 7.0) and several organic solvents was assessed and partition coefficients calculated. Purification of cytokinins from plant extracts by solvent partition methods is discussed.
Although plant extracts are frequently partitioned between water and organic solvents to purify cytokinins, no information is available concerning partition coefficients for naturally occurring cytokinins. The distribution of kinetin between water and solvents has been studied and it has been suggested that the distribution of naturally occurring cytokinins would be similar (Hemberg and Westlin, 1973). However, this conclusion would appear to be unjustified.
In this communication, the partition coefficients for five naturally occurring cytokinins and for the synthetic cytokinin, kinetin (6-fuffurylaminopurine), are compared. The availability of certain of these cytokinins in radioactive form enabled us to determine their partition coefficients accurately at physiological concentrations.
The following radioisotopically labelled cytokinins were used: 1) [G-aH]zeatin (190 mC/mmol), prepared according to Letham and Young (1971); 2) [8-1aC]kinetin (15 mC/mmol), purchased from the Radiochemical Centre, Amersham, U.K.; 3) [2,8-aH]6-(3-methylbut-2-enylamino)purine (399 mC/mmol), prepared by refluxing [2,8-3tt]6-ehloropurine with 3-methylbut-2-enylamine in 1,2-dimethoxyethane; and 4) [aH]zeatin riboside (190 mC/mmol). This riboside was prepared by hydrolysis with alkaline phosphatase from E. coli of [aH]zeatin riboside-5'monophosphate extracted from the hypocotyls of de-rooted radish seedlings supplied with [G-aH]zeatin through the transpiration stream (see Parker and Letham, 1973). Solutions of the radioisotopieally labelled cytokinins (0.20 tzM) in aqueous buffer (0.03 M potassium citrate, pH 3.0; 0.03 M potassium phosphate, pH 7.0) were shaken with an equal volume of water-saturated organic solvent at 23 ~ Aliquots of the separated phases were evaporated in scintillation vials and the residues were *XX: Letham, DS., Physiol. Plantarum (Cph.), in press.