Transients in O2 Evolution by Chlorella in Light 



and Darkness 

 I. Phenomena and Methods 



F. 8. BRACKETT, R. A. OLSON, and R. G. CRICKARD, Laboratory of 



Physical Biology, Xational Institute of Arthritis and Metabolic Diseases, 



National Institutes of Health, Public Health Service, United States Department 



of Health, Education, and Welfare, Bethesda, Maryland 



This paper and the one following will present studies of "early 

 transients" in photosynthesis by Chlorella. These observations have 

 been made possible by the development of an electronically recording 

 instrument which measures both the concentration of oxygen and the 

 rate of change of concentration. 



"Early transients" seem to have a wide \'ariety of meanings with 

 times ranging from milliseconds to hours, depending on the time reso- 

 lution of the instruments employed. Our instrument provides dis- 

 cretely new values every 3 seconds, in contrast to 10-second intervals 

 in our earlier work. Furthermore, the evaluation of slope depends 

 upon the difference of two adjacent values where formerly we re- 

 quired the tangent to three points. Thus our time resolution is im- 

 proved threefold for concentration and nearly sevenfold for rate. 

 WTiereas rotating or flowing types of electrodes provide still more 

 rapid response (1), we have found them nonlinear and capricious (2), 

 as others have also reported. 



Our method of oxygen determination depends as before (2) on im- 

 posing an alternating square potential pattern on a static platinum 

 electrode and recording the current for a short period just at the end 

 of the negative phase. Tests show that the shorter cycle still results in 

 independent values for each point and linear dependence of magnitude 

 on oxygen concentration. 



A t>T3ical pen recording of concentration is shown above in Fig. 1, 

 with periods of increase and decrease corresponding to hght or dark. 

 A simultaneous recording of slope or rate is obtained by a second pen 

 writer as shown below. The background "noise" or uncertainty in 



412 



