Changes in Endogenous Plant Hormones in the Xylem Sap of Grapevines during Development

Abstract

Endogenous plant hormone levels in the xylem sap of the grapevine were determined at different stages of development to demonstrate the relationship between top growth arid endogenous plant hormones.
(1) The growth of the new shoot was a typical double sigmoid curve. The inception of the second growth was at a full bloom stage. The growth of roots increased rapidly after the shoot growth stopped.
(2) Cytokinin activities in the xylem sap were present in n-butanol (Free) and aqueous (Bound) fractions, In each fraction there were at least two major peaks of cytokinin activities.
(3) The free cytokinins increased from April to July, and thereafter decreased rapidly. The bound cytokinins were maintained at high levels from May to June as flowers opened. Gibberellin-like activity in the xylem sap was present in May and increased in June as flowers opened and fruits developed, and thereafter decreased rapidly. Auxin and absccisic acid-like activities in the xylem sap were very low during their development.
These results lead to the suggestion that gibberellin and cytokinin synthesized in roots may play an important physiological role in controlling the growth of the shoot and flower clusters.