417 



George Hoch and Olga v. H. Owens 



In this case we consider the response of oxygen production 

 and uptake to increasing intensities of 710 mu light when 

 this light is added to a sample in the dark or to a sajnple 

 already illuminated with 63O mu light. In the first case 

 oxygen production is a linear function of 710 mu intensity. 

 Oxygen uptake shows the characteristic inhibition at this 

 wavelength. The net gas exchange curve will of course show 

 a break. Now we do the same tyoe of experiment as done by 

 Jones and Myers ^■'-■^^ and put the same 710 mu light on a back- 

 ground of 630. The curve now rises quickly, due, of course, 

 to enhancement, until it has "titrated" the available short 

 wavelength photoproduct and then resumes the slope found for 

 the far red alone. The ratio of slopes in this experiment 

 is 6.3* 



Now the crux of the experiment is the response of oxygen 

 uptake during the addition of the 710 mu light to the 63O mu 

 light. The figure shows that in the 63O light alone oxygen 

 uptake is increased and that addition of the 710 mu beam 

 suppresses this Ujptake. The suppression is essentially com- 

 plete at the lowest intensity of far red light used. Be- 

 cause of the scatter in the data v;e obtain in this type of 

 experiment we are unwilling to place much emphasis on the 

 apparent kinetics. Better instrumentation is required to 

 resolve this. Nevertheless, it appears to us that during 

 the intensities in v;hich the far red beam is being enhanced 

 (the steep slope), oxygen uptake is being suppressed. If 

 these results are correct, suppression of uptake is not 

 competitive with enhanced oxygen production, but rather the 

 tv/o can occur simultaneously. 



Discussion 



The results show that respiratory changes can and do 

 cause many anomalies when the net rate of gas exchange is 

 taken as a measure of photosynthesis. In our experiments 

 we have observed a remarkable linearity of actual oxygen 

 production as a function of light intensity over the lower 

 intensity regions. The respiratory effects are clearly the 

 source of many discrepancies in the measurement of the 

 quantum yield of photosynthesis as a function of wavelength, 

 they also provide explanation for the puzzling phenomen of 

 "negative" enhancement. Perhaps other observations of Emer- 

 son such as the extension of the good quantum yields of 

 photosynthesis into the far red by such means as the addi- 

 tion of yeast extract or earth extract or low temperature 



