Glutamine synthetase catalyses the synthesis of glutamine from glutamate and ammonia, which is one of the key enzymes involved in nitrogen metabolism of plants. Two classes of glutamine synthetase are present in plants, cytosolic form (GLN1) and chloroplastic form (GLN2) . While GLN1 is encoded by five genes (AT5G37600, AT1G66200, AT3G17820, AT5G16570, AT1G48470) , GLN2 is encoded by a single gene (AT5G35630) .
