Changes in Net O2 Exchange Induced by Inorganic Nitrogen in the Blue-Green Alga Anacystis nidulans

The response of net O(2) exchange to light intensity by intact Anacystis nidulans cells in the presence of saturating NaHCO(3) concentrations followed a curve with an inflection near the light-compensation point. Addition of either KNO(3) or NH(4)Cl stimulated O(2) uptake in the dark and at light intensities below the light-compensation point. This resulted in steeper slopes of the curve calculated below and above the light-compensation point. At O(2) concentrations limiting dark respiration, addition of inorganic nitrogen had no effect on either dark respiration or O(2) exchange in the light. The apparent changes in photosynthetic yield observed under normal O(2) concentration disappeared when respiration was limited by O(2) availability, indicating that the effects of inorganic nitrogen on O(2) exchange at low light intensities are due to stimulation of respiration rather than to increases in photosynthetic yield.