Light regulation of glutamine synthetase in the green alga Monoraphidium braunii

• Published in: Journal of plant physiology Vol. 146; no. 5; pp. 577 - 583
• Main Authors: García-Fernández, J.M., López-Ruiz, A., Alhama, J., Diez, J.
• Format: Journal Article
• Language: English
• Published: Jena Elsevier GmbH 1995; Elsevier
• Subjects: Algae; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; glutamine synthetase; light-regulation; Metabolism; Monoraphidium; Monoraphidium braunii; Nitrogen metabolism; Plant physiology and development; light-regulation; CCCP; MSX; DTE; NR; glutamine synthetase; Algae; DCMU; Monoraphidium; GS; DCCD; Carbon-nitrogen ligases; Enzyme; Chlorophycophyta; Regulation(control); Enzymatic activity; Ligases; Nitrate reductase; Light; Developmental stage; Oxidoreductases; Glutamate-ammonia ligase; Thallophyta
• ISSN: 0176-1617; 1618-1328
• DOI: 10.1016/S0176-1617(11)81917-6

Glutamine-synthetase (GS; EC 6.3.1.2) and nitrate-reductase (NR; EC 1.6.6.2) activity and protein levels were measured in crude extracts from alga Monoraphidium braunii Näegeli, strain 202-7d, cultures grown under different illumination conditions. GS did not exhibit significant variations under continuous light. However, if cultures were grown under light/dark cycles three peaks of GS activity and two of GS protein were detected during the course of the day. On the other hand, only one peak of both NR activity and protein was found under these conditions. A different response was also observed when cultures growing either under light/dark cycles or continuous light were transferred to darkness: in the first case GS activity was strongly inactivated while GS protein levels did not change significantly; in the second case GS activity and protein decreased in parallel. The effect of darkness on GS and NR depended on the age of the cultures and was prevented by glucose addition. These results together with those obtained with photosynthesis inhibitors point out the energy state of the cells as the mediatory agent for light-promoted GS regulation. Studies performed in the presence of methionine sulf oximine (MSX) under darkness allow to propose that the energy state of the cells plays a more important role than nitrogen source on GS regulation in Monoraphidium.