Abstract
Apple rootstocks M.7 were kept in a greenhouse (20°C) at root temperatures of about 6 and 20°C. Xylem sap was sampled periodically for 5 weeks starting at budbreak, and was analysed for the cytokinins trans-zeatin (Z), trans-zeatin riboside ([9R]Z), isopentenyl-adenine (iP), and isopentenyl-adenosine (9[9R]iP) using indirect competitive 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 the sap. Shoot growth was markedly reduced at the lower root temperature.
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