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Effects of Light Intensity and Oxidized Nitrogen Sources on Hydrogen Production by Chlamydomonas reinhardii

Pedro J. Aparicio, María P. Azuara, Antonio Ballesteros and Victor M. Fernández
Plant Physiology
Vol. 78, No. 4 (Aug., 1985), pp. 803-806
Stable URL: http://www.jstor.org/stable/4269431
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Effects of Light Intensity and Oxidized Nitrogen Sources on Hydrogen Production by Chlamydomonas reinhardii
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Abstract

Chlamydomonas reinhardii cells, after a period of dark anaerobic adaptation, evolve H2 not only in the dark but also in the light. Our results show that high irradiances impair prolonged H2 evolution, while under low irradiances or darkness H2 evolution proceeds for more than 50 hours. NO3 - and $NO_{2}{}^{-}$ suppress H2 evolution both in the dark or under low irradiance. Apparently the cells prefer these oxidized nitrogen sources to protons as electron acceptors, since both NO3 - and $NO_{2}{}^{-}$ become reduced to NH4 +, which is excreted to the culture medium in high amounts. H2 evolution started once these oxidized anions were largely depleted from the medium. Moreover, H2 evolution was consistently associated with NH4 + excretion even if NH4 + was already present in high amounts in the medium. This observation indicates that the cells utilize not only their carbohydrate but also their protein reserves as sources of reducing power for H2 evolution. This conclusion was supported by the observation that when nitrogen-starved cells were made anaerobic in a nitrogen-free medium, they not only evolved H2 at very high rates but excreted concomitantly NH4 + up to concentrations in the millimolar range.

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