Experimental researches on vegetable assimilation and respiration. XXI.—Induction phases in photosynthesis and their bearing on the mechanism of the process

Abstract

The moss Mnium undulatum was used for most of the work with a gas mixture of 4-5% COa diluted with hydrogen. The gas mixture was circulated by a pump and the oxygen produced removed by palladium black. There is a tendency for the ratio of the average rate in the first 10 minutes to the final rate to increase with rising temperature up to 25[degree]C. and the ratio is higher when the illumination is low. Using the data obtained two theories of the mechanism of photosynthesis are put forward. The first has already been described in Proc. Fifth Internat. Bot. Congr. (1930), Cambridge. Certain modifications in this theory have to be made to get good agreement between theory and experimental values for the first 10 minutes but the fit is good for later periods. A second theory is now brought forward which accounts for the induction period as well as the final rate. "A complex of some substance we will call S (which may be chlorophyll) and carbon dioxide is converted to S1 as a result of absorption of light energy. This latter substance, perhaps a peroxide form, may be broken down by a catalyst B to give carbohydrate and oxygen, or alternatively it may decompose an inhibitor which is produced by the cell and which combines with B, but not competing with S1, and acts as a depressant.".