ISHS Acta Horticulturae 146: International Workshop on Controlling Vigor in Fruit Trees
PHYSIOLOGICAL CHANGES INDUCED BY PACLOBUTRAZOL (PP333) IN APPLE |
| Authors: | G.L. Steffens, S.Y. Wang |
| Abstract:
Apple seedlings, 'York Imperial' (M. domestica Borkh.) were greenhouse-grown in nutrient solution and treated by wetting stems and leaves (roots were untreated) with 0.1 mM (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2(1,2,4-triazol-l-yl)pentan-3-ol (paclobutrazol; PP333). After 21 days, PP333 had reduced weight and leaf area of new shoots, but increased weight, diameter and length of fibrous roots as well as leaf chlorophyll content on a area basis. Total plant weight was not markedly changed. Carbohydrate concentrations increased in the uppermost leaves, all stem portions and especially in fibrous roots of PP333-treated seedlings. Sorbitol was the predominant non-structural carbohydrate in leaves and stems whereas starch predominated in fibrous roots. Fibrous roots from shoots which had been treated with PP333 showed the same total respiration as control plants but the alternate or CN-resistant pathway contributed 67% to the total respiration in the case of the PP333-treated plants. For control plants only the cytochrome pathway contributed to respiration. Some other metabolic changes caused by PP333 treatment included the evolution of less CO2 in the dark by excised shoots, the loss of less water by treated plants, reduction in ethylene evolution by leaves from treated plants when placed under water stress and the loss of less moisture per unit time from treated leaves. Weight of new leaves and stems from PP333-treated plants grown with roots at 30°C for 37 days was reduced to a greater percentage than for plants with roots at 14.5°C. The respiration of fibrous roots of plants grown at 14.5°C was lower than for plants grown at 30°C but PP333 treatment caused the alternate pathway to be engaged at both temperatures. PP333 treatment increased carbohydrates in plants grown at both 14.5 and 30°C and altered the organic acid composition of treated leaves. | |
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