Does Light Inhibit the Respiration of Green Cells? 



101 



however low, a light intensity exists that will compensate respiration, as we have 

 confirmed when we have used light of sufficiently high intensity. 



Our experiments show conclusively that red light does not inhibit the respiration 

 per se when light intensities are employed that yield high photosynthetic efficiencies. 

 When light compensates respiration it does so by the independent process of 

 photosynthesis, the gas exchange of which happens to be the opposite of that of 

 respiration. This result has been confirmed in a different way by determination and 

 comparison of photosynthetic efficiency below and above the compensation point. 

 Under the conditions of our experiments, reported in detail elsewhere*, the same 

 high quantum efficiencies of 3 — 5 quanta per O2 are obtained up to intensities at 

 least five times the compensating intensity. That is, one molecule of oxygen deve- 

 loped above the compensation point, or one less molecule of oxygen consumed 

 below the compensation point, as the result of light action, represents the same 

 gain in chemical energy. All theories of light action should be in harmony with this 

 nowestablished thermodynamic fact. 



Example 



Each of three vessels contained 230 mm. 3 aliquots of Chlorella pyrenoidosa cells suspended in 7 cc. 

 of culture medium (5 g. MgS0 4 ■ 7H 2 0, 2.5 g. KN0 3 , 2,5 g. KH2PO4, 2 g. NaCl, and 5 mg. 

 FeSOi • 7H'iO in 1 1. of filtered, unsterilized well water at pH 4.5 — 5). Temperature, 20° C. 

 Horizontal shaking at the rate of 150 cycles/min. at 2 cm. amplitude. Total intensity of red light 

 beam (630 — 660 »i,k), 0.254 microeinsteins/min., equivalent actinometrically to 5.7 mm. 3 Oe/min. 



No. I. 0.2 cc. N NaOH in each side-arm, gas phase air. 



(Vessel volume 18.87 cc, liquid volume 7.40 cc, ko 2 1.09) 



X02 



*02 



43.5 mm. 3 

 1.09 mm. 3 



105 



No. II. Gas phase 5% CO2 in air, respiration not compensated by white light. 



Vessel 3 



Vessel 5 



— 0.8 



* In press, Science and Biochim. Biophys. Acta (Meyerhof Festschrift, October, 1949); and 

 report delivered at meeting of Society of General Physiologists, Woods Hole, Mass., June 22. 1949. 



