Production of Oxygen by Illuminated Chloroplasts

Abstract

THE activity of isolated chloroplasts in light, measured by the oxygen evolved from ferric oxalate, has been shown to be relatively high. The ferric oxalate is reduced to ferrous oxalate and oxygen, which is equivalent to the iron reduced, and was measured by means of hæmoglobin. The maximum pressure of oxygen obtainable, however, was only 4 mm. mercury^1,2. It has now been proved, by direct measurement of the oxidation of ferrous oxalate, that this low limit of oxygen pressure obtainable simply results from the re-oxidation of the ferrous oxalate produced by the illuminated chloroplasts. If the oxygen uptake due to the oxidation of the ferrous salt can be prevented, oxygen should accumulate to a higher pressure and be capable of direct measurement. It was found that ferricyanide rapidly oxidizes ferrous oxalate in the presence of excess of potassium oxalate.