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A. Pérez-García S. Pereira J. Pissarra A. García Gutiérrez F. M. Cazorla R. Salema A. de Vicente F. M. Cánovas 《Planta》1998,206(3):426-434
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.
Received: 16 January 1998 / Accepted 21 April 1998 相似文献