Growth and metabolism of soybean as affected by paclobutrazol
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Paclobutrazol, an experimental growth retardant, was soil-applied at the rate of 125 or 250 g active ingredient per 10 cm pot to 19 day-old soybean plants. This compound considerably reduced plant height, leaf area, and stem dry weight. In addition, paclobutrazol-treated plants had numerous thickened lateral roots at the soil surface and had increased chlorophyll and soluble protein contents compared to controls. During the first 14 days after treatment, paclobutrazol increased the activities of NAD- and NADP-glyceraldehyde-3-phosphate dehydrogenase and aminotransferases but decreased the activity of nitrate reductase. Net photosynthesis (Pn) of the first and second trifoliates of treated plants remained fairly constant throughout the study while control Pn declined during the latter portion of the experimental period presumably due to leaf senescence. This decline of Pn in controls was accompanied by a decrease in the activities of NAD- and NADP-glyceraldehyde-3-phosphate dehydrogenase, nitrate reductase, aminotransferases, and NAD malate dehydrogenase. Activities of these enzymes also tended to decline in paclobutrazol-treated plants, but were still considerably higher than in controls at the end of the experiment. The activities of RNase, protease, and glutamic dehydrogenase were higher in controls than in treated plants. Our results suggest that paclobutrazol not only modifies the activity of a number of soybean enzymes but also delays the onset of senescence, thereby prolonging the period of normal metabolic activity in a given leaf. 1985 The Japanese Society of Plant Physiologists.
