Effect of nitrate-N incorporation on the composition of the intracellular amino acid pool of N-deprivedTetraselmis marina

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Abstract
The major free amino acids in N-replete cells of Tetraselmis marina were arginine, taurine, glutamate, glutamine, aspartate, asparagine, serine and alanine. During N-deprivation in light, levels of all of these decreased; free α-amino-N decreased by 85% after 72 h N-deprivation. In contrast, cells deprived of N in darkness accumulated free amino acids in their pool, presumably reflecting the need for products of photosynthesis for processes of amination and protein synthesis. When cells N-deprived in light were supplied with a pulse of NO- 3, there was a slow increase in levels of each amino acid, but levels similar to those in N-replete cells were not attained within 48 h of pulsing. The only major amino acids showing a significant response within 24 h of pulsing were arginine, ornithine, and glutamine. The slow return to levels found in N-replete cells is suggested to be a consequence of the complex interaction between the pathways leading to the synthesis of individual amino acids coupled with the removal of amino acids for protein synthesis. Despite this, the qualitative composition of the amino acid pool (by rank) was remarkably conservative, only differing significantly in cells subjected to prolonged N-deprivation in light.

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