SPRING CYTOKININ COMPOSITION OF XYLEM SAP OF APPLE AT 2 ROOT TEMPERATURES

Apple rootstocks M.7 were kept in a greenhouse (20-degrees-C) at root temperatures of about 6 and 20-degrees-C. Xylem sap was sampled period ically for 5 weeks starting at budbreak, and was analysed for the cyto kinins trans-zeatin (Z), trans-zeatin riboside ([9R]Z), isopentenyl-ad enine (iP), and isopentenyl-adenosine (9[9R]iP) using indirect competi tive enzyme immunoassays. The initially rather high concentrations of all compounds dropped rapidly after leafing out. Usually, more than 80 % of total cytokinins were accounted for by Z and [9R]Z. In general, [ 9R]Z predominated. There was hardly any effect of root temperature on total cytokinins and on the composition of the cytokinin fraction of t he sap. Shoot growth was markedly reduced at the lower root temperatur e.