Sugar, Amino Acid and Inorganic Contents in Rice Phloem Sap

Rice phloem sap was obtained through severed stylets of brownplanthoppers and its chemical composition was determined. Sucrose,the only sugar detected, was present at 17–25% (w/v) inthe sap. Amino acids were present at a total of 3–8% (w/v)and were found to be mostly in a free form. The amount of boundamino acids was estimated to be small, if any were present.Among the free amino acids, asparagine (17–33% on a molarbasis), glutamate (6–14%), serine (10–13%), glutamine(7–15%), threonine (5–6%) and valine (6–7%)were dominant, while cystine and methionine (0–0.2%) werepresent in minor amounts and -aminobutyric acid was not detected.The sap had a slightly alkaline pH (ca. 8.0). The inorganicconstituents detected by electron probe x-ray microanalyzerwere Na, S, P and K, with the K content being the highest. Theosmotic pressure was estimated to be 13–15 atm. The aminoacid composition of the plant parts was determined and the differencesin the ease of phloem loading among amino acids were compared. (Received October 5, 1981; Accepted December 17, 1981)