The isolation and some properties of a lectin (Haemagglutinin) from Cucurbita phloem exudate

The occurrence of high haemagglutinating (lectin) activity in phloem exudate from three cucurbit species is reported. The protein responsible for this lectin activity in Cucurbita maxima Duch. has been isolated by cation exchange chromatography on Sepharose and identified by gel electrophoresis. The lectin showed agglutinating activity at concentrations as low as 0.1 g/ml. No sugar, including those transported in the phloem of these species, interacted with agglutination. The lectin could not be extracted from cucurbit seed, but appeared in 5-day old seedlings. The possible role of a lectin in the sieve element is discussed.