252 



E. KESSLFJR 



in the dark. The results are shown in Table I. A decrease in tem- 

 perature from 15°C. to 4°C. inhibits nitrite reduction in the dark and 

 in the light in the presence of CO2 by about 50%. In the light with- 



140 



QUINONE 



NITRITE 



NITRATE 



60 90 



MINUTES 



Fig. 1. Evolution of oxygen after addition of quinone, NaN02, and KNO3 (no 

 addition as control) to Ankistrodesmus braunii suspended in N-free culture me- 

 dium (pH 6.5) in the absence of CO2. Gas phase N2 (KOH in the center well); light 

 intensity 13,000 lux; temperature 15°C.; 21 mm.^ cells (6.5 mg. dry weight) per 

 vessel. Concentrations of oxidants: Quinone 3.3 X 10~' mole per liter; NaNOo 

 1.1 X 10-3 jnole per Uter; KNO, 8.3 X 10"^ mole per Uter. Theoretical yield: 

 179 mm. '02 in each case. Pretreatment of the algae: 4 hours in N-free medium 

 at moderate light intensity (4000 lux); gas phase air. 



out CO2, however, nitrite reduction is decreased by only 15%. The 

 favorable influence of CO2 on the reduction of nitrite almost disap- 

 pears at 4°C. Light under anaerobic conditions in the absence of COi 

 is much more effective in nitrite reduction than is respiration in the 

 dark. This especially holds true at 4°C., where the rates of enzymatic 

 reactions are strongly decreased. 



