Premium
THE MECHANISM OF ISOTOPE FRACTIONATION DURING ALGAL NITRATE ASSIMILATION AS ILLUMINATED BY THE 15 N/ 14 N OF INTRACELLULAR NITRATE 1
Author(s) -
Needoba Joseph A.,
Sigman Daniel M.,
Harrison Paul J.
Publication year - 2004
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.2004.03172.x
Subject(s) - nitrate , fractionation , nitrate reductase , isotope fractionation , stable isotope ratio , nitrogen assimilation , biology , environmental chemistry , intracellular , chemistry , biochemistry , chromatography , ecology , physics , quantum mechanics
The 15 N/ 14 N of nitrate in the external medium and intracellular pool of the cultured marine diatom Thalassiosira weissflogii (Grun.) Fryxell et Hasle was measured during nitrate assimilation under low light, a 12:12‐h light:dark cycle, low temperature, or low iron conditions. The 15 N/ 14 N of the nitrate in the medium and the particulate matter both followed the predicted Rayleigh fractionation model, and the intracellular nitrate always had a higher 15 N/ 14 N than did the medium nitrate. When the experiments were compared, the results showed a negative correlation between the isotope fractionation factor and the difference in the 15 N/ 14 N between the two pools of nitrate. These observations imply that the variations in the isotope effect result from variations in the degree to which the fractionation by nitrate reductase is expressed outside the cell, which is, in turn, controlled by the rate of nitrate efflux relative to nitrate reduction. The low iron and low temperature experiments showed relatively small isotope effects but a large intracellular‐medium difference in nitrate 15 N/ 14 N, consistent with a relative rate of efflux (compared with influx) that is small and similar to fast‐growing cells. In contrast, large isotope effects and small intracellular‐medium differences in nitrate 15 N/ 14 N were observed for low light and light:dark cycle grown cells and are explained by higher relative rates of nitrate efflux under these growth conditions.