Sunflower cytosolic-glutamine-synthetase genes showing similar organ-specificity patterns exhibit very different expression intensities by reverse-transcription polymerase chain reaction and Northern analysis

Four genes coding for the cytosolic isoforms of glutamine synthetase (GS; E C 6.3.2.1) were recently identified in sunflower. The levels of transcripts from those genes have been analyzed in selected organs where ammonium is b eing produced by different processes that might differentially regulate the genes' expression. Genes exhibiting consistently high (ggs1.1 and -1.4), l ow (ggs1.2), and very low (ggs1.3) expression have been found. However, the four cytosolic-GS genes were expressed according to very similar patterns of organ specificity suggesting a low degree of specialization within this gene family in sunflower.