Differential Expression of Glutamine Synthetase Isoforms in Tomato Detached Leaflets Infected with Pseudomonas syringae pv. tomato. Alejandro Perez-Garcia. Departamento de Microbiologia, Facultad de Ciencias, Universidad de Malaga, E-29071 Malaga, Spain. Francisco M. Canovas(2), Fernando Gallardo(2), Bertrand Hirel(3), and Antonio de Vicente(1). (1) Departamento de Microbiologia (2)Laboratorio de Bioqufmica y Biologia Molecular, Facultad de Ciencias, Universidad de Malaga, E-29071 Malaga, Spain (3) Laboratoire du Metabolisme, I.N.R.A., route de St-Cyr, 78026 Versailles, France. MPMI 8:96-103. Accepted 24 October 1994. Copyright 1995 The American Phytopathological Society.

Expression of glutamine synthetase (GS) isoforms of tomato leaflets was investigated (luring the infection by Pseudomonas syringae pv. tomato. Glutamine synthetase activity decreased markedly when it was determined by synthetase assay, but when GS activity was evaluated by transferase assay a not so strong decline was observed. Two GS molecular forms were separated by ion-exchange chromatography in noninfecled and in chlorotic detached leaves. In noniufected leaves the major peak elulcd at about 0.22 M KC1; however, in chlorotic leaves the major peak eluted at about 0.15 M KCI. A GS polypeptide of 45 KDa was the major species detectable by Western blot analysis of noninfected leaves; however, a second band of 39 KDa was the major GS species detectable in chlorotic leaves. Western and Northern blot analysis from infected detached leaflets in different stages of pathogenesis showed a decrease of GS polypeptide of 45 KDa and its specific mRNAs and an increase of GS species of 39 KDa and its transcripts. Our results suggest that during the infection there is a change in the GS isoform pattern and cylosolic GS (GS-1) replace chloroplastic GS (GS-2). Se ha investigado la expresion de glutamina sintetasa (GS) en hojas de tomate infectadas por Pseudomonas syringae pv. tomato. Durante la infeccion, la actividad GS dis-minuyo drasticamente cuando se determino mediante el ensayo sintetasa, pero con el ensayo transferasa no se ob-servo un descenso tan acusado. Mediante cromatograffia de intercambio ionico se separaron dos formas molecu-lares de GS tanto en hojas sanas como en infectadas. En hojas control el pico mayoritario de actividad GS eluyo a 0.22 M de KCI, mientras que en hojas infectadas lo hizo a 0.15 M. El inmunoanalisis revelo un polipeplido de GS de 45 kDa como la forma mayoritaria en hojas sanas, mientras que una segunda banda de 39 KDa fue la especie mayoritaria en hojas infectadas. El analisis mediante Western y Northern blot durante la infeccion, revelo un descenso de los niveles del polipeptido de GS de 45 KDa y de su mRNA especifico, y un aumento de los niveles de la especie de 39 kDa y de su correspondientc mRNA. Nuestros resultados sugieren que durante la infeccion hay un cambio en el patron de isoformas de GS, y la forms citosolica de la enzima (GS-1) reemplaza a la isoforma cloroplastidica (GS-2)