Nitrate Reductase Activity of Photoautotrophic Suspension Culture Cells of Chenopodium rubrum is under the Hierarchical Regime of NO_3^-, NH_4^+ and Light

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During batch culture of photoautotrophic cells of Chenopodium rubrum under long-day illumination regime a growth phase of three weeks was followed by a stationary phase of another six weeks. During the growth phase two thirds of the nitrate and 85 percent of the NH^+_4 in the medium were consumed. Uptake of both ions was only observed during the light period. Nitrate reductase (but none of the other enzymes of nitrate assimilation) exhibited pronounced diurnal fluctuations above a basic activity. Both the basic and the superimposed diurnally oscillating activity slowly but continuously declined and virtually disappeared in cultures older than seven weeks. The oscillations were due to light triggered protein synthesis. However, nitrate uptake from the medium or NO^-_3 remobilization from the vacuole was a prerequisite for the de-novo synthesis of NR, suggesting the requirement of a 'metabolic pool' of nitrate for the inductive process. Uptake as well as remobilization of NO^-_3 depended pivotally on the presence of comparatively high concentrations of ammonium (20 mM) in the medium.
日本植物生理学会の論文