Chemical Composition of Phloem Sap from the Uppermost Internode of the Rice Plant

The chemical composition of phloem sap from the uppermost internodeof rice plants (Oryza sativa L., var. Kantou), one week afteranthesis, was compared with that of phloem sap from the leafsheath of a young seedling. The pure phloem sap from rice plantswas collected by an insect laser technique. The phloem sap from the uppermost internode contained a highlevel of sucrose (573.8 mM) which was the only sugar detected.The concentrations of total amino acids, potassium and ATP were124.8 mM, 40.4 mM and 1.76 mM, respectively. The concentrationof sucrose was three times higher and the potassium level wasone third as high in the internode sap as in the phloem sapfrom the leaf sheath. The total concentration of amino acidswas almost the same, but the relative amount of each amino acidwas quite different. The ratios of levels of Glu to Gln andof levels of Asp to Asn in the phloem sap from the uppermostinternode were smaller than those in the phloem sap from theleaf sheath. The adenylate energy charge was 0.92–0.93in both types of phloem sap. The amino acid composition of the phloem sap from the uppermostinternode was compared with that of the phloem sap of the flagleaf and the endosperm sap of the same plant, one week afteranthesis. The differences in composition along the phloem pathwaysuggest the selective translocation of amino acid. (Received July 21, 1989; Accepted December 11, 1989)