Assimilate Transport in Cucurbits

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Abstract
The long-distance transport of sugars has been investigated in cucurbits. 14C-labelled sugars were applied to an abraded leaf surface and the content of 14C in various fractions of extracts from leaf blade, petiolar tissue, and phloem exudate subsequently determined. Nearly one half of the 14C activity determined in the phloem sap was in amino and organic acids, the other half in sugars, whereas in leaf and petiolar tissue most of the 14C activity was found in the neutral sugar fraction. As the solute concentration of cucurbit phloem sap is relatively low the calculated rate of mass transfer would require high transport velocities and large areas of phloem. However, the driving force for such translocation is not known.