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Plant Physiology 66:383-389 (1980)
© 1980 American Society of Plant Biologists

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Articles

Steady-state Growth of the Marine Diatom Thalassiosira pseudonana

UNCOUPLED KINETICS OF NITRATE UPTAKE AND NITRITE PRODUCTION 1

Robert J. Olson

Janice Beeler Soohoo and Dale A. Kiefer

Institute of Marine Resources, A-018, Scripps Institution of Oceanography, La Jolla, California 92093, Department of Biological Sciences, University of Southern California, Los Angeles, California 90007

Seasonal studies of the vertical distribution of nitrate, nitrite, and phytoplankton in the oceans and studies using 15N as a tracer of nitrate metabolism indicate that the reduction of nitrate by phytoplankton is a source of nitrite in the upper waters of the ocean. To better understand this process, the relationship between nitrate uptake and nitrite production has been examined with continuous cultures of the small marine diatom Thalassiosira pseudonana. In a turbidostat culture, the rates of nitrite production by T. pseudonana increase with light intensity. This process is only loosely coupled to rates of nitrate assimilation since the ratio of net nitrite production to total nitrate assimilation increases with increased rates of growth. In continuous cultures where steady-state concentrations of nitrate and nitrite were varied, T. pseudonana produced nitrite at rates which increased with increasing concentrations of nitrate. Again, the rates of nitrite production were uncoupled from rates of nitrate assimilation. The study was used to derive a mathematical description of nitrate and nitrite metabolism by T. pseudonana.

The validity of this model was supported by the results of a study in which 15N-labeled nitrite was introduced into the continuous culture, and the model was used to examine patterns in distribution of nitrite in the Antarctic Ocean and the Sargasso Sea.

1 This study was supported by the United States Department of Commerce, National Oceanic and Atmospheric Administration, National Environmental Satellite Service Grant 04-7-158-44123, by Department of Energy Contract DE-AC03-79EV70020, and by DePaul University Grant C-816302.






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Copyright © 1980 by the American Society of Plant Biologists