Effects of Manipulations of Source and Sink on the Carbon Exchange Rate and Some Enzymes of Sucrose Metabolism in Leaves of Soybean [Glycine max (L.) Menr.]

Soybean plants [Glycine max (L.) Merr. cv. AGS129], two and three weeks after depodding and defoliation, respectively, were used to examine the possibility of end-product regulation on the carbon exchange rate and activities of enzymes involved in sucrose metabolism in leaves. Removal of one and two lateral leaflets per trifoliate leaf reduced the total leaf area by 20 % and 47%, respectively. Removal of one pod per node reduced the total pod number by 23 % per plant. Dry weights of roots, stems and petioles decreased with reductions in leaf area. By contrast, removal of pods resulted in an increase in these parameters. The carbon exchange rate and transpiration rate of leaves increased with defoliation and decreased with depodding. The intercel-lular concentration of CO2 in leaves was reduced by defoliation and increased by depodding. Fur-thermore, defoliation increased the level of leaf chlorophyll in leaves while depodding decreased it. Removal of pods decreased the activities of sucrose-phosphate synthase and a-amylase but in-creased that of sucrose synthase. A significant positive correlation was found between the activity of leaf sucrose-phosphate synthase and both the carbon exchange rate and the sucrose content of leaves. Thus, manipulation of the sink and source in soybean plants influenced the relationship be-tween sucrose metabolism and the carbon exchange rate in intact leaves