Characteristics of sugar uptake in hypocotyls of cotton.

Uptake of sucrose and hexoses by cotton (Gossypium hirsutum L.) hypocotyl segments from free space was shown to be an active, carrier-mediated process. Separate carriers existed for hexoses and sucrose. Accumulated sugars appeared in both soluble and insoluble fractions of the tissue. At optimum temperature and pH, sucrose uptake rate versus concentration was fit by a rectangular hyperbola with V(max) of 14 micromoles per gram fresh weight per hour and K(m) of 8 mm. Sucrose was the principal sugar found in the free space in vivo, and invertase activity was essentially absent from that space except after aging.