Mechanism of Organic Translocation in Straight-Neck Squash

The mechanism of organic translocation in Cucurbita pepo L. variety melopepo torticollis was investigated. Two-centimeter petiole sections from nodes 2 and 3 of 22-day squash were analyzed colormetrically for the concentration of stachyose and sucrose. Stachyose is an important transport molecule and, in contrast to sucrose, may be localized in the phloem. This investigation attempted to determine the possibility of stachyose being further localized in a particulate cell fraction. The volume of the phloem was determined to be 20 mm3 per petiole. The concentration of stachyose per petiole, assuming that all of the stachyose was in the phloem and that the stachyose was evenly distributed in the phloem, was calculated to be between 0.3 and 0.4 molar. The molar concentration of sucrose in the phloem was calculated to be between 0.25 and 0.35. A fructose density-gradient with minimum and maximum amounts of fructose being 100 and 350 mg/ml, respectively, was used to isolate a fraction rich in stachyose. It was determined that 50 percent of the stachyose was localized in a 3 ml portion of the 14 ml gradient. These data provide additional evidence to support the theory that phloem transport occurs by means of particulates which move in or on transcellular strands