ISSN:
1432-2048
Keywords:
Key words: Glutamine synthetase
;
Lycopersicon
;
Nitrogen remobilization
;
Phosphinothricin
;
Plant defense
;
Pseudomonas
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract. 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004250050418
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