PHOTOCHEMICAL XITRATE REDUCTION 255 



Tolbert: How many plant tissues have you tried? 



Kessler: These experiments have been done only with Ankistrodesmus cells. 



Myers: Following such nitrite reduction as you observed, do the cells remain 

 viable? 



Kessler: Yes, they do. 



Kamen : Nitrite is verj- closely associated with some hemoproteins, and it may 

 be that there maj' be an inhibition on this ground, if the nitrate reduction of this 

 particular organism goes through a C5'tochrome. Verhoeven and Takeda got a 

 preparation from Pseudomonas aeruginosa which contained a flavin protein that 

 activated the reduction of both nitrate and nitrite by reduced cytochrome c. 

 This means very likely, although not necessarily, that there may be some c}i:o- 

 chrome involved in the reduction of the nitrite in this particular organism. 



Gibbs : You measured only nitrite reduction. Did you deter m ine whether some 

 of the nitrite was going back to nitrate? 



Kessler : I have made tests for nitrate after nitrite reduction. Thej^ were always 

 negative. 



M. B. Allen : I would like to saj- that no reduction of nitrate in the absence of 

 COa is not necessarily a general phenomenon in algae. We have carried out a ver)- 

 appreciable reduction of nitrate with Chlorella in the absence of CO2. In fact, the 

 amount of ox3'gen produced from nitrate when CO2 was absent was comparable 

 to the excess of oxygen over CO2 which we obtained in the presence of nitrate. 

 Since we know that algal metaboUsm is a rather plastic thing, it seems to me not 

 unreasonable that we could get conditions in which nitrate reduction and carbo- 

 hydrate metabolism were mixed up together. 



Kessler: There might be differences between different strains. But, as far as 

 nitrate reduction in the light is concerned, the results obtained with Ankistrodes- 

 mus are almost identical with those of Davis with Chlorella. In both cases no ap- 

 preciable reduction of nitrate occurs in the light unless COi or glucose is present. 



M. B. Allen : But we can take one Chlorella strain under different conditions 

 and it will change its habits. The point which I wish to make is that the interrela- 

 tion between carbon metabolism and nitrate reduction may depend on how the 

 alga has been cultivated. 



References 



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2. Warburg, O., and Negelein, E., Biochem. Z., 110, 66 (1920). 



3. Burstrom, H., Ann. Agr. Coll. Swed., 11, 1 (19-43). 



4. Myers, J., in Photosynthesis in Plants, J. Franck and W. E. Loomis, eds., p. 



349. Iowa State College Press, Ames, Iowa, 1949. 



5. Rabinowitch, E. I., Photosynthesis and Related Processes, Vol. 1, Interscience, 



New York, 1945. 



6. Evans, H. J., and Nason, A., Plant Physiol, 28, 233 (1953). 



7. van Niel, C. B., Advances in Enzymol., 1, 263 (1941). 



8. Mendel, J. L., and Visser, D. W., Arch. Biochem. and Biophys., 32, 158 



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9. van Niel, C. B., Allen, M. B., and Wright, B. E., Biochim. et Biophys. Acta, 



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