ISOFORMS OF GLUTAMINE SYNTHETASE DURING BARLEY FLAG LEAF SENESCENCE UNDER FIELD

NADIA ROLNY; LORENZA COSTA; ZSCHIESCHE W; KLAUS HUMBECK; JUAN JOSÉ GUIAMET

Potrero de lo Funes, San Luis

Congreso; SAIB, th 47 Annual Meeting Argentine Society for Biochemistry and Molecular Biology-XLVII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2011

SAIB

In senescing leaves, a large amount of ammonium is produced as a result of protein hydrolysis. Most of the ammonium is reassimilated into amino acids for export from the senescing leaf, whereas a minor part is evaporated as ammonia from the leaf canopy. Glutamine synthetase (GS) is a key enzyme involved in this process. According to their subcellular localization cytosolic GS (GS1) and chloroplastic GS (GS2) are distinguished. While GS2 is encoded by one gene, GS1 is encoded by 3?5 genes depending on the species. The roles of the different isoforms of GS1 are still unresolved. During leaf senescence cytosolic GS1 fulfills a key function in the assimilation and recycling of ammonia. This role is particularly important during grain development and filling in cereals, when nitrogen is remobilised. We analysed ammonium acumulation in barley flag leaf senescence under two N fertilization conditions. The total chlorophyll and protein content decreased, while ammonium content increased during senescence. A significant decrease of GS activity was observed. Symptoms of senescence appeared latter in plants grown with high N. We have also investigated the expression of senescence associated GS genes by real-time PCR. We have identified at least three GS1 barley genes; one of them increased during senescence and was downregulated by N. Supported by PIP 0599 and DAAD 0409.