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) MERR]

Soybean plants [Glycine max (L.) Merr. cv. AGS129], two and three week s 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. Re moval of one and two lateral leaflets per trifoliate leaf reduced the total leaf area by 20% and 47%, respectively. Removal of one pod per n ode reduced the total pod number by 23% per plant. Dry weights of root s, stems and petioles decreased with reductions in leaf area. By contr ast, removal of pods resulted in an increase in these parameters. The carbon exchange rate and transpiration rate of leaves increased with d efoliation and decreased with depodding. The intercellular concentrati on of CO2 in leaves was reduced by defoliation and increased by depodd ing. Furthermore, defoliation increased the level of leaf chlorophyll in leaves while depodding decreased it. Removal of pods decreased the activities of sucrose-phosphate synthase and alpha-amylase but increas ed that of sucrose synthase. A significant positive correlation was fo und between the activity of leaf sucrose-phosphate synthase and both t he carbon exchange rate and the sucrose content of leaves. Thus, manip ulation of the sink and source in soybean plants influenced the relati onship between sucrose metabolism and the carbon exchange rate in inta ct leaves.