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Marine Ecology Progress Series

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MEPS 122:253-263 (1995)  -  doi:10.3354/meps122253

Nitrogen assimilation following NH4+ pulses in the red alga Gracilariopsis lemaneiformis: effect on C metabolism

Vergara JJ, Bird KT, Niell FX

The short-term effect of external NH4+ availability on N assimilation, as well as on C metabolism, has been studied in the red alga Gracilariopsis lemaneiformis. This agarophyte seaweed showed a high capacity to take up external NH4+ and to channel it toward proteins. As in a previous study in Corallina elongata, it appears that N limitation redirected the flow of internal N toward nonpigmented proteins, whereas phycobiliprotein synthesis was preferentially stimulated with respect to other proteins in response to external NH4+ pulses. A possible mechanism by which chloroplastic protein synthesis is limited by external N availability more than cytosolic proteins could be involved. In relation to C metabolism, insoluble and soluble carbohydrates were mobilized in response to NH4+ assimilation at a non-saturating irradiance for photosynthesis of 80 umol m-2 s-1. The main change in C metabolism was not seen for total C. The principal effect was the flow of C among different compounds, from carbohydrates to organic N compounds (amino acids and proteins) during transient NH4+ assimilation.

Ammonia · Nitrogen assimilation · Carbon · Carbohydrates · Phycobiliproteins · Gracilariopsis · Rhodophyta

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