428 R. A. OLSON, F. S. BRACKETT, R. G. CRICKARD 



of no CO2 uptake is found immediately following illumination. This 

 offers additional evidence for the dissociation of the oxygen burst 

 process from that of CO2 fixation. 



In a recent report (5) a form of convective polarography is used to 

 measure marked O2 concentration changes occurring immediately on 

 illumination of Chlorella suspensions under anaerobic conditions 

 (0.001% O2). The report offers the conclusion, viz., that the beginning 

 of photosynthesis does not require oxygen, since the cells contain a 

 substance which in light is capable of releasing a limited amount of 

 oxygen, and that the sustained rate of photosynthesis is initiated by 

 respiration stimulated by this oxygen. Attention is called to the fact 

 that this work is subject to the quantitative limitations of convection 

 polarography (12-14) and the condition of saturating hght intensities 

 in the presence of O2 (0.001%). We find it difficult to reconcile the 

 above interpretation with our finding of marked dependence of the 

 initial O2 burst upon oxygen concentration (or the immediately prior 

 dark oxidation rate) . Moreover, no O2 dependence of sustained rate is 

 indicated in (15). 



In a later publication further correlation of our findings with other 

 related plienomena will be considered. 



Acknowledgment. The authors express appreciation of the technical as- 

 sistance of Mrs. E. Engel, both in the experimental procedure and the culture 

 of Chlorella. 



Discussion 



Bassham : In our closed gas circulating system, with an instrument which 

 measures a specific property of oxygen, paramagnetism, and another instrument 

 which measures CO2, so that the two are independent of each other, we have 

 observed transients in both oxygen and carbon dioxide. I cannot remember anj' 

 detailed results because we have not made a systematic study of the effects, but 

 I can say that these transients vary not onh' in their size but also in their direc- 

 tion, depending on light intensity and previous condition of the plant and manj- 

 other factors. I simply mention that there are some transients in both oxygen and 

 carbon dioxide. I cannot say more at this time about what their size and order are. 



Rosenberg : I wonder if you could review for me how excessive the initial respira- 

 tion was in the first instant of dark after a normal preceding period of photosyn- 

 thesis. 



Brackett: It very commonly doubles. In other words, the first spike is perhaps 

 double the sustained rate of respiration. 



Rosenberg : And in the inhibited cell sometimes it went to 3 or 4? 



Brackett : Oh, yes, many times, but onl}' in the inhil)ited cells. 



Wassink : It seems to me that the picture you find in the time course, similar 

 to the first outburst of fluorescence, is very much exaggerated at low concentra- 



