Table 3.

Effect of hexoses and mannoheptulose on sucrose transport activity

Exp.	Treatment solution	Transport activity, pmol/mg protein·min
A	Water	1,161  ±  12
	Sucrose (100 mM)	416  ±  3
	Glucose (100 mM)	818  ±  15
	Fructose (100 mM)	820  ±  15
	Glucose + fructose	828  ±  16
B	Water	1,071  ±  70
	Mannoheptulose (10 mM)	972  ±  43
	Sucrose (100 mM)	355  ±  24
	Sucrose + mannoheptulose	437  ±  25

In experiment A, sugar beet leaves were fed water, 100 mM sucrose, 100 mM glucose, 100 mM fructose, or 100 mM glucose plus 100 mM fructose for 10 h. Plasma membrane vesicles were isolated from the treated leaves and sucrose transport activity was assayed in vitro. In experiment B, leaves were fed water or 100 mM sucrose in the presence or absence of 10 mM mannoheptulose for 11 h. Plasma membrane vesicles were isolated from the treated leaves and sucrose transport activity was assayed in vitro.