Amino acid and sucrose content determined in the cytosolic, chloroplastic, and vacuolar compartments and in the phloem sap of spinach leaves

• Published in: Plant physiology (Bethesda) Vol. 97; no. 1; pp. 227 - 233
• Main Authors: Riens, B. (Universitat Gottingen, Gottingen, Federal Republic of Germany), Lohaus, G, Heineke, D, Heldt, H.W
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.09.1991
• Subjects: ACIDE AMINE; Amino acid metabolism; Amino acids; AMINOACIDOS; Biological and medical sciences; CARBOHIDRATOS; CHLOROPLASTE; CITOPLASMA; CLOROPLASTO; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; Corn; CYTOPLASME; Cytosol; FEUILLE; FISIOLOGIA VEGETAL; FLOEMA; FOTOSINTESIS; Fundamental and applied biological sciences. Psychology; GLUCIDE; HOJAS; Leaves; Metabolism; Metabolism. Physicochemical requirements; METABOLITE; METABOLITOS; Phloem; PHLOEME; PHOTOSYNTHESE; PHYSIOLOGIE VEGETALE; Plant physiology and development; Plants; SACCHAROSE; SAVIA; SEVE; Sieve tubes; Spinach; SPINACIA OLERACEA; SUCROSA; VACUOLA; VACUOLE; Vacuoles; Translocation; Sap; Sucrose; Plant leaf; Spinacia oleracea; Vacuole; Chenopodiaceae; Phloem; Vegetable crop; Dicotyledones; Aminoacid; Angiospermae; Spermatophyta; Chloroplast; Cytoplasm
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.97.1.227

Amino acid and sucrose contents were analyzed in the chloroplastic, cytosolic, and vacuolar compartments and in the phloem sap of illuminated spinach leaves (Spinacia oleracea L.). The determination of subcellular metabolite distribution was carried out by nonaqueous fractionation of frozen and lyophilized leaf material using a novel three-compartment calculation method. The phloem sap was collected by aphid stylets which had been severed by a laser beam. Subcellular analysis revealed that the amino acids found in leaves are located mainly in the chloroplast stroma and in the cytosol, the sum of their concentrations amounting to 151 and 121 millimolar, respectively, whereas the amino acid concentrations in the vacuole are one order of magnitude lower. The amino acid concentrations in the phloem sap are found to be not very different from the cytosolic concentrations, whereas the sieve tube concentration of sucrose is found to be one order of magnitude higher than in the cytosol. It is concluded that the phloem loading results in a preferential extraction of sucrose from the source cells