Nitrate Reductase Activity of Photoautotrophic Suspension Culture Cells ofChenopodium rubrumis under the Hierarchical Regime of NO3-, NH4+and Light

摘要

During batch culture of photoautotrophic cells ofChenopodium rubrumunder 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 theNH4+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 orNO3−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 ofNO3−depended pivotally on the presence of comparatively high concentrations of ammonium (20 mM) in the