Phloem transport of amino acids in relation to their cytosolic levels in barley leaves

• Published in: Plant physiology (Bethesda) Vol. 99; no. 3; pp. 996 - 1004
• Main Authors: Winter, H. (Universitat Gottingen, Gottingen, Germany), Lohaus, G, Heldt, H.W
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.07.1992
• Subjects: ACIDE AMINE; Amino acid metabolism; Amino acids; AMINOACIDOS; ANALISIS CUANTITATIVO; ANALYSE QUANTITATIVE; Barley; Biological and medical sciences; CITOPLASMA; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; CYTOPLASME; Cytosol; FEUILLE; FLOEMA; FOTOSINTESIS; Fundamental and applied biological sciences. Psychology; HOJAS; HORDEUM VULGARE; Leaves; LUMIERE; LUZ; Mesophyll cells; Metabolism; Metabolism and Enzymology; METABOLISME; METABOLISMO; METABOLITE; METABOLITOS; OBSCURIDAD; OBSCURITE; Phloem; PHLOEME; PHOTOSYNTHESE; Photosynthesis, respiration. Anabolism, catabolism; Plant physiology and development; Plants; RITMOS BIOLOGICOS; RYTHME BIOLOGIQUE; Sieve tubes; TRANSPORT DES SUBSTANCES NUTRITIVES; TRANSPORTE DE NUTRIENTES; Vacuoles; Translocation; Monocotyledones; Fractionation; Sap; Hordeum vulgare; Sucrose; Plant leaf; Source sink relationship; Vacuole; Cereal crop; Assay; Phloem; Gramineae; Aminoacid; Angiospermae; Spermatophyta; Chemical composition; Conductive tissue; Chloroplast; Cytoplasm
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.99.3.996

A comparison of barley (Hordeum vulgare L.) leaves was made between the cytosolic content of amino acids and sucrose as determined by subcellular fractionation and the corresponding concentration in phloem sap, which was collected continuously for up to 6 days from severed aphid stylets. Because amino acids were found to be almost absent from the vacuoles, and because the amino acid patterns in the stroma and cytosol are similar, whole leaf contents could be taken as a measure of cytosolic amino acid levels for a comparison of data during a diurnal cycle. The results show that the pattern of amino acids in the phloem sap was very similar to the pattern in the cytosol. Therefore, we concluded that the overall process of transfer of amino acids from the cytosol of the source cells into the sieve tubes, although carrier mediated, may be a passive process and that the translocation of amino acids via the sieve tubes requires the mass flow of sucrose driven by the active sucrose transport involved by the phloem loading