Proteins and Carbohydrates in Xylem Sap from Squash Root

摘要

The xylem sap from squash roots was collected from the cut surface of stems, and the proteins and carbohydrates in the sap were analyzed. The sap contained 18.6μg ml−1protein and the major polypeptides were as follows: 1) two polypeptides, of 75 and 40 kDa, with high-mannose glycans, the levels of which increased for about 24 h after cutting and then decreased; 2) a 32-kDa polypeptide, which appeared soon after cutting, disappeared and then reappeared again 48–64 h after cutting; and 3) a 19-kDa and a 14-kDa polypeptide, which were present constitutively. The carbohydrates contained in the xylem sap were fractionated into 80ethanol-soluble and -insoluble material, and which were analyzed by high-performance liquid chromatography, gas chromatography and enzymatic mathods. The former fraction contained considerable amounts of myo-inositol and fructose as free sugars and oligosaccharides composed mainly of galactose, arabinose and glucose. The latter contained polysaccharides composed mainly of uronic acids, galactose and arabinose. The possible significance of these substances, which may mediate the interactions between the root and the aerial organs, is discu