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Regulation of glutamine synthetase expression in sunflower cells exposed to salt and osmotic stress

2004; Elsevier BV; Volume: 103; Issue: 1 Linguagem: Inglês

10.1016/j.scienta.2004.04.010

1879-1018

Conceição Santos, Anabela Pereira, Susana Pereira, Jorge Teixeira,

Legume Nitrogen Fixing Symbiosis

Sunflower (Helianthus annuus L. cv. SH222) plants and calluses were exposed to 100 mM NaCl and to osmotic stress induced by polyethylene glycol 6000 (PEG 6000; 50 g/l). Salt and osmotic stresses increased cytosolic glutamine synthetase (GS1) mRNA and the corresponding polypeptides in plants. In calluses, GS1 mRNA and polypeptide contents increased in response to salt stress. Determination of glutamine synthetase isoenzyme activities showed increases of GS1 activity in NaCl-stressed cells (increases of 3.5; 6.2 and 1.3 times, respectively in leaves, roots and calluses) and in PEG-stressed plants (increases of 4.0 and 6.9 times in leaves and roots, respectively), while plastidial glutamine synthetase (GS2) activity decreased in NaCl-stressed leaves. This increase of GS1 expression was accompanied by an increase of ammonium levels in stressed leaves. This report shows that NaCl and osmotic stresses induced GS1 expression by increasing GS1 mRNA and polypeptide leading to increased enzymatic GS1 activity. These data confirm previous suggestions about the increase of GS1 expression in senescent cells and support the role of this isoenzyme on nitrogen mobilization in plant cells.