Regulation of sugar uptake in hypocotyls of cotton.

Uptake of sucrose and hexoses by hypocotyl segments of cotton (Gossypium hirsutum L.) was shown to be dependent upon sugar level in the tissue. The effect was not related to total sugar level inasmuch as a portion of previously accumulated sugar was without influence on uptake. That portion was presumed to be compartmentalized, most likely in vacuoles. Growth regulators modified the uptake pattern apparently through alterations in secondary metabolism. Uptake and incorporation were inhibited by rotenone and stimulated by light. The light effect was blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. A general model was presented for assimilate flux within sink tissues with free space as the conduit from phloem to carrier site.