THE QUANTUM YIELD OF OXYGEN PRODUCTION BY CHLOROPLASTS SUSPENDED IN SOLUTIONS CONTAINING FERRIC OXALATE

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Abstract
Since the discovery of the evolution of oxygen by illuminated chloroplasts by Hill in 1937, the question has been raised whether or not this phenomenon is a part of the photosynthetic reaction proper. If one could show a quantum yield for this phenomenon consistent with the accepted algal photosynthesis quantum yields of Emqrson and Lewis, and Stauffer, Duggar and Daniels, one might conclude that this reaction could be a part of, or closely related to, the photosynthetic reaction proper. The pressure of the 02 produced when spinach chloroplast suspen- sions were illuminated with a band of light from 660 to 720 [mu] in width was measured with a differential manometer. After measuring the light intensity in absolute energy units, and correcting for the fraction of light reflected and transmitted by the manometric vessel, the quantum yield was calculated. For spinach, and for Tradescantia sp. between 0.013 and 0.08 (average 0.032), molecules of O2 were produced per quantum of energy. This variation was attributed to activity differences in market spinach, since reproducible values were obtained when duplicate determinations were made on the same lot of spinach. While the average efficiency of the spinach chloroplasts is about i that of normal photosynthesis, the higher values are within the efficiency range of normal photosynthesis. So far the quantum yield data do not indicate a fundamental difference between photosynthesis and the in vitro production of O2 from an artificial substrate.

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