ISHS Acta Horticulturae 80: Symposium on Growth Regulators in Fruit Production
A POSSIBLE ROLE OF HORMONES IN GROWTH AND DEVELOPMENT OF APPLE TREES AND A SUGGESTION ON HOW TO MODIFY THEIR ACTION |
| Authors: | M.J. Grochowska, A. Karaszewska |
| Abstract:
To establish a direct relationship between some endogenous hormones and growth a comparison of their levels and sequence in pruned and unpruned young apple trees was carried out during the first few months of vegetation for two years. Free auxin, gibberellins /GAs/ and cytokinins were investigated in trunks /xylem sap and phloem tissues/ and annual shoots /current year/ according to the method described by Shindy and Smith /1975/. Specific bioassays were applied for the estimation of hormone activities. A total level of the three hormones was, on an average, higher in pruned trees than in unpruned controls. Cytokinins were the most abundant in conducting tissues of the trunk at the very beginning of growth; their level was doubled by pruning. In pruned trees the auxin level also rose twice in the midle of June as compared to that of controls. Gibberellins reached their maximum 3 weeks later. The rapidly rising level of GAs in the trunks preceded about 2 weeks a period of the extension growth of shoots. However, in the annual shoots GAs level was inversely related to their growth. Shoot cytokinins were, on the other hand, doubled in the unpruned trees in July /flower bud differentiation period/ when compared to the pruned trees which remained mostly vegetative. To modify action of endogenous hormones via the respiratory system phloridzin, phloretic acid /PA/ and p-coumaric acid were applied to the trees as sprays. All compounds inhibited a respiration rate of leaves of apple trees of different ages. Phloridzin and PA markedly increased flowering of branches when they were applied into fruitlets after removing seeds. The possible role of these hormones in apple trees is discussed. | |
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