The Assimilation of Ammonia by Nitrogen-starved Cells of Chlorella vulgaris

Abstract

The addition of ammonium sulphate to a suspension of nitrogen-starved Chlorella cells is followed immediately by the rapid assimilation of ammonia and a large increase of the respiration rate. The assimilation of ammonia and the high rate of respiration continue until either all the ammonia has been assimilated or some carbon reserve within the cells has been exhausted. Which happens first depends on the amount of ammonia added and the quantity of cells present. The respiration which accompanies, ammonia assimilation is sensitive to cyanide and it has a respiratory quotient of 0⋅75 compared with 1⋅2–1⋅3 for normal reapiration. The addition of glucose to nitrogen-starved cells when ammonia is being assimilated does not increase either the rate of respiration or the rate of assimilation. The rates of reapiration and ammonia assimilation by normal cells are markedly increased by the addition of glucose. Light has little effect on the rate of ammonia assimilation by nitrogen-starved cells, but doubles the assimilation rate of normal cells.