Cytosolic localization in tomato mesophyll cells of a novel glutamine synthetase induced in response to bacterial infection or phosphinothricin treatment

• Published in: Planta Vol. 206; no. 3; pp. 426 - 434
• Main Authors: Perez-Garcia, A, Pereira, S, Pissarra, J, Garcia Gutierrez, A, Gazorla, F.M, Salema, R, Vicente, A. De, Canovas, F.M
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-10-1998; Springer
• Subjects: Amino acids; Bacterial plant pathogens; Biological and medical sciences; Chloroplasts; cytosol; enzyme inhibitors; epidermis; Fundamental and applied biological sciences. Psychology; glufosinate; glutamate-ammonia ligase; immunocytochemistry; infection; Infections; isozymes; Leaves; mesophyll; Mesophyll cells; Metabolism; Nitrogen; Nitrogen metabolism; Pathology. Damages, economic importance; Phloem; Phytopathology. Animal pests. Plant and forest protection; Plant cells; Plant physiology and development; plant veins; Plants; Protein isoforms; Pseudomonas syringae pv. tomato; quantitative analysis; Solanum lycopersicum var. lycopersicum; Pseudomonadales; Ammonium; Plant pathogen; Isozyme; Identification; Cytosol; Ligases; Dicotyledones; Angiospermae; Lycopersicon esculentum; Bacteria; Pseudomonadaceae; Solanaceae; Localization; Glutamate-ammonia ligase; Carbon-nitrogen ligases; Enzyme; Induction; Tissue specificity; Host agent relation; Defense; Infection; Vegetable crop; Spermatophyta; Biological accumulation
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s004250050418

In tomato (Lycopersicon esculentum Mill.) leaves, the predominant glutamine synthetase (GS; EC 6.3.1.2) is chloroplastic (GS2; 45 kDa) whereas the cytosolic isoform (GS1; 39 kDa) is represented as a minor enzyme. Following either infection by Pseudomonas syringae pv. tomato (Pst) or treatment with phosphinothricin (PPT), a GS inhibitor, GS1 accumulated in the leaves. In contrast to healthy control leaves. where GS1 was restricted to the veins, in infected and PPT-treated leaves the GS1 polypeptide was also detected in the leaf blade, moreover, it was more abundant than GS2. Different immunological approaches were therefore used to investigate whether or not the GS1 polypeptide expressed in Pst-infected and PPT-treated tomato leaves was distributed among different tissues and subcellular compartments in the same way as the constitutive GS1 expressed in healthy leaves. By tissue-printing analysis, a similar GS immunostaining was observed in epidermis, mesophyll and phloem of leaflet midrib cross-sections of control, infected and PPT-treated leaves. Immunocytochemical localization revealed that GS protein was present in the chloroplast of mesophyll cells and the cytoplasm of phloem cells in healthy leaves; however, in Pst-infected or PPT-treated leaves, a strong labelling was observed in the cytoplasm of mesophyll cells. Two-dimensional analysis of GS polypeptides showed that, in addition to the constitutive GS1, a GS1 polypeptide different in charge was present in tomato leaflets after microbial infection or herbicide treatment. All these results indicate that a novel cytosolic GS is induced in mesophyll cells of Pst-infected or PPT-treated leaves. A possible role for this new cytosolic GS in the remobilization of leaf nitrogen during infection is proposed.