Changes in photosynthesis, IAA export from leaves and cytokinins in the xylem sap after girdling of young mango trees in combination with different growth regulators and their possible significance for flower induction.
Hegele M., Boonplod N., Bangerth F., Naphrom D., Chattrakul A., Sruamsiri P., Manochai P.
Author Affiliation: Dept. of Horticulture, University of Hohenheim, Institut Obst Gemuse und Weibau Emil-Wolf Str 25, Stuttgart, 00070-593, Germany.
: 417-424
Abstract : Young, potted mango cv. Talabnak trees were mechanically girdled, and part of the girdled trees were additionally chemically girdled with two auxin transport inhibitors (morphactin (CME) and naphthyl-phthalamic acid (NPA)). Treatments comprised: control, girdling, girdling + NPA, girdling + CME. Leaf photosynthesis, transpiration and stomatal conductance of 6 trees per treatment were measured at 1, 3, 5, 9 and 14 days after treatment. After 1, 3 and 14 days, leaf diffusates for hormone analysis were sampled. Although none of the treatments induced flowering in the young trees, all treatments reduced photosynthesis, transpiration and stomatal conductance for at least 14 days. All treatments conspicuously affected the IAA export out of the leaves. Both combinations of girdling and auxin transport inhibitor showed only a moderate reduction in diffusible IAA one day after the allocation of the treatments. Two days later, a sharp rise in IAA diffusion could be observed, irrespective of the treatments. With values of ~250% over the controls, it was most pronounced in girdling±NPA. Cytokinins (CKs) in the xylem sap of the treated trees increased significantly. A hypothesis trying to explain how IAA export from leaves and CKs from roots could induce mango trees to flower even under non-inductive temperatures, is presented.