Oxygen produced by isolated chloroplasts

Abstract The system concerned with the assimilation of carbon dioxide by the green plant has, under optimum conditions, an activity comparable with the highest rate of cellular respiration in animals. At the moment there is, in the case of animals, considerable knowledge of the subcellular chemical mechanisms which can be connected with respiratory activity. In the green plant, on the other hand, there is still no direct indication of a single chemical mechanism connected with carbon assimilation. As the oxygen output, apart from CO2 evolution is a guide in searching for systems connected with respiration, so might an oxygen output, apart from CO2 absorption, indicate mechanisms characteristic of photosynthetic activity in the plant. The subcellular evolution of oxygen under illumination has been known in the case of green plants for many years (Spoehr 1926). The effect, however, was always insignificant compared with the original photosynthetic activity of the cell. The oxygen could only be detected by using certain bacteria which show either motility or luminescence with traces of this gas. But to this method we owe the classical investigations of Engelmann (Spoehr 1926) who showed that in the living cell oxygen appeared in the neighbourhood of the illuminated chloroplast and the experiments on the isolated chloroplasts of Funaria hygrometrica by Haberlandt, who demonstrated the production of oxygen in light. Ewart (1896) confirmed and extended these results using other mosses and Selaginella helvetica; in a phanerogam, Elodea, no oxygen could be observed to come from the isolated chloroplastes. The same problem was approached in a somewhat different manner by Molisch (1925). The leaves of many phanerogams were allowed to dry slowly in air and finally over a dehydrating agent. This produced a stable preparation which, if ground up in water, would show an evolution of oxygen in light which could be detected by the bacterial methods. Molisch showed that these preparations were thermolabile, indicating an enzymic process. Recently, the matter was taken up by Inman (1935) who confirmed the experiments of Molisch and showed also that fresh green extracts of many phanerogams will evolve oxygen in light, using the bacterial mathod. Inman brought further evidence as to the enzymic nature of the process, and, moreover, did not consider the oxygen evolved to represent photosynthesis but suggested that it was due to a limited store of oxygen-giving material.