Translocation of Sugars in Cucurbita melopepo IV. Effects of Temperature Change

A study has been made of the temperature control of translocation localized to regions of the stem, petiole and hypocotyl of Cucurbita melopepo. The basipetal and acropetal movement of translocated (14)C-labeled compounds in the phloem tissue, measured over a 45-minute period, was almost completely inhibited at 0 degrees . At 10 degrees a partial inhibition occurred while an extremely variable degree of inhibition occurred at 15 degrees . Above 15 degrees to 35 degrees temperature ceased to be a limiting factor in the movement of (14)C-labeled compounds. At 45 degrees partial inhibition was observed while at 55 degrees there was an almost complete cessation. The localized temperature treatment of the plant parts did not disturb the rate of (14)CO(2) assimilation or the export of (14)C compounds by the leaf blade. Translocated compounds unable to pass a temperature inhibited zone were diverted toward other importing regions of the plant. The similarity of the translocation response to temperature change in the various organs of the plant indicated a uniform mechanism throughout the plant controlling movement of the major proportion of the translocated compounds. The temperature characteristics of the mechanism were found to closely parallel those of protoplasmic streaming in chill-sensitive plants.