ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
BIOCHEMICAL AND PHYSIOLOGICAL ALTERATIONS IN APPLE TREES CAUSED BY A GIBBERELLIN BIOSYNTHESIS INHIBITOR, PACLOBUTRAZOL |
| Authors: | G.L. Steffens, S.Y. Wang |
| Abstract:
Investigations of the effects of the triazole plant growth inhibitor, paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl) pentan-3-ol)], on apple seedlings and bearing apple trees show it to be more effective for inhibiting shoot elongation and leaf area expansion than for reducing leaf number. Foliar application of gibberellic acid (GA3 or GA4/7) to inhibited plants temporarily counteracted growth inhibition, as well as some of the associated physiological and biochemical changes. Apple seedlings inhibited by paclobutrazol treatment contained higher levels of nonstructural carbohydrates in all portions. Orchard-grown cv. 'Spartan' trees had higher levels of nonstructural carbohydrates in both shoot and spur leaves but not in fruit flesh. Both inhibited and non-inhibited wood from treated trees during winter and spring periods also contained higher concentration of nonstructural carbohydrates. Chlorophyll levels in leaves from treated seedlings were greater but this was not always the case for shoot and fruiting spur leaves on orchard-grown trees. Soluble protein closely paralled chlorophyll content. Paclobutrazol treatment could cause the engagement of the alternative respiratory pathway of nutrient solution-grown seedling roots as well as increase rate of root respiration. Mineral element composition of leaves from nutrient solution-grown seedlings was altered to a greater degree than leaves of orchard-grown trees but fruit flesh and skin remained unchanged. Paclobutrazol reduced water loss and prevented accumulation of water stress-induced l-aminocyclo-propane-l-carboxylic acid (ACC); l-(malonylamino)cyclopropane-1-carboxylic acid (MACC); ethylene production; and polyamine content in apple seedling leaves. | |
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