The Chemical Composition of Cucurbit Vascular Exudates

The organic and inorganic solute content of phloem and root pressure exudate from cucurbits was determined. The range of values obtained for the solutes in phloem sap indicated that cucurbit phloem sap was dissimilar in a number of respects from the phloem saps of other species. It has a high protein content and low total sugar content, and also contains a high proportion of the sugar as monosaccharides. The phloem exudate also has features typical of other phloem saps, e.g. high pH and K+ concentration. These data provide an indication of which solutes are translocated, providing a quantitative basis for further studies on photoassimilate loading and translocation in cucurbits.