Regulation of nitrate assimilation in the cyanobacterium Phormidium laminosum

• Published in: Planta Vol. 198; no. 1; pp. 24 - 30
• Main Authors: Tapia, M.I, Llama, M.J, Serra, J.L
• Format: Journal Article
• Language: English
• Published: 1996
• Subjects: 2-oxoglutarate; ammonium compounds; assimilation; carbon; cell suspension culture; enzyme activity; ferredoxin nitrate reductase; ferredoxin nitrite reductase; glutamate synthase; glutamate-ammonia ligase; glutamine; nitrates; nitrogen; nitrogen metabolism; nutrient deficiencies; nutrient solutions; nutrient-nutrient interactions; oxidoreductases; Phormidium
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/BF00197582

The intracellular ratio of 2-oxoglutarate to glutamine has been analyzed under nutritional conditions leading to different activity levels of nitrate-assimilating enzymes in Phormidium laminosum (Agardh) Gom. This non-N2-fixing cyanobacterium adapted to the available nitrogen source by modifying its nitrate reductase (NR; EC 1.7.7.2), nitrite reductase (NiR; EC 1.7.7.1) and glutamine synthetase (GS; EC 6.3.1.2) activities. The 2-oxoglutarate/glutamine ratio was similar in cells adapted to grow with nitrate or ammonium. However, metabolic conditions that increased this ratio [i.e., nitrogen starvation or L-methionine-D,L-sulfoximine (MSX) treatment] corresponded to high activity levels of NR, NiR, GS (except in MSX-treated cells) and glutamate synthase (GOGAT; EC 1.4.7.1). By contrast, metabolic conditions that diminished this ratio (i.e., addition of ammonium to nitrate-growing cells or addition of nitrate or ammonium to nitrogen-starved cells) resulted in low activity levels. The variation in the 2-oxoglutarate/glutamine ratio preceded the changes in enzyme activities. These results suggest that changes in the 2-oxoglutarate/glutamine ratio could be the signal that triggers the adaptation of P. laminosum cells to variations in the available nitrogen source, as occurs in enterobacteria.