311 



Jack Myers 



possibility that the effect might be associated vith a respira- 

 tory anomaly, with changes in respiratory oxygen uptake rather 

 than with changes in oxygen production. In at least one alga, 

 Anacystis, the question has been answered unequivocally by the 

 mass spectrometer experiments of Hoch, Owens and Kok. We inter- 

 pret their results as follows: (l) there are effects of low light 

 intensity on respiration, most pronounced in the Xi region; 

 (2) these are of such a nature that they may obscure or decrease 

 enhancement effects as observed in temis of net oxygen productlcn; 

 and (3) the enhancement effect is not caused by changes in re- 

 spiratory oxygen uptake. 



The important experiments of Hoch et_al."^® provided an explana- 

 tion of the Kok effect^^ -vrfaich we also observed in Anacystis. Our 

 studies with the Blinks- Haxo electrode were less definitive in 

 that they measured only changes in net oxygen production. How- 

 ever, their greater precision and rapidity led to results which 

 further broaden the interpretation. ^ 



Fig. 6 demonstrates the Kok effect in Anacystis as a sharp 

 break in slope of the light intensity curve at very low intensity. 

 The effect is observable by our measurements only at wavelengths 

 of the \i region. Further, curves A, B, and C for the different 

 wavelengths extrapolate to a common intercept. Following the re- 

 sults of Hoch etal., we attribute the high initial slopes 

 (curves A, B, C) to the combined effects of decreasing rate of 

 oxygen uptake and an increasing rate of oxygen production. The 

 lower final slopes represent only increasing rate of oxygen pro- 

 duction superimposed upon a lowered, but now constant, rate of 

 oxygen uptake. 



Fig. 7 shows the change in rate of net oxygen evolution in re- 

 sponse to intensity at 700 mu when added to a constant background 

 intensity of chosen wavelength. The reference curve A (dark 

 background) is taken from the previous set of measurements with- 

 out correction for a measured lO^o decay in response between the 

 two sets. Curve E, with constant 700 mt-i background, shows only 

 one linear segment extrapolating to zero but otherwise correspond- 

 ing to the second slope of curve A. The respiratory decrease has 

 been saturated and its effect wiped out by the 700 mM background. 

 Conversely, curves F and G on 620 mn- background have an initial 

 slope essentially the same as the slope of curve A and prolonged 

 to an extent dependent on background intensity. Curves F and G 

 demonstrate enhancement between the constant 620 my. background 

 and the varying 700 my. As expected, both curves approach the 

 same final slope, common also to cu2rves A and E, as the 620 my- 



