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Seasonal Variation in the Hormone Content of Willow

I. Changes in Abscisic Acid Content and Cytokinin Activity in the Xylem Sap ¹

^a Department of Botany and Microbiology, University College of Wales, Aberystwyth, Wales

Changes in levels of abscisic acid (ABA) and cytokinin activity in the xylem sap of willow (Salix viminalis, L.) were followed throughout two growth cycles.

Growth in spring was preceded by decreasing levels of ABA and an increase in cytokinin activity. The onset of dormancy was associated with low levels of cytokinins and high contents of ABA. A second peak of ABA was found in July which was not related to the dry weight of the sap. The main cytokinin activity in the sap was due to a zeatin riboside-like compound.

¹ This paper represents part of the Ph.D. dissertation of R.A., whose work was supported by the Conselho Nacional de Pesquisas (Brazil) and by the Ministry of Overseas Development (Great Britain).