The reduction of ferric oxalate by isolated chloroplasts

Abstract

1.The isolated chloroplasts from Stellaria media show a progressive fall in activity approaching zero in 3-6 hr. Four different strains of the plant were grown which showed differences in the stability of chloroplasts after removal. 2. Two methods have been used to measure the activity of chloroplasts: (a) The measurement with HbO₂ of oxygen produced from ferric potassium oxalate as previously described. (b) The measurement of the rate of reduction of methaemoglobin in presence of atmospheric oxygen, the methaemoglobin being reduced by the ferrous iron. 3. The Q_o2, measured as rate of oxygen production calculated on the basis of dry weight of leaf taken, is about 20. The Q_o2, measured as rate of methaemoglobin reduction, generally appeared less as the reduction of methaemoglobin by ferrous iron is relatively slow. 4. The reduction of methaemoglobin in presence of ferric potassium oxalate has been studied quantitatively from the point of view of iron, methaemoglobin, and chloroplast concentration. 5. The effect of different light intensities on the ferric oxalate reaction is similar to the effect of varying light intensity on photosynthesis in whole plants and lies within the range of values found by different workers. 6. The ferric oxalate reaction is inhibited by urethane. Phenyl urethane inhibits in much smaller concentrations than ethyl urethane. The effective concentrations of urethane are similar to those affecting photosynthesis. 7. It is concluded from the present observations that the light reaction in vegetable photosynthesis is the production of the oxygen molecule and is not the reduction of carbon dioxide.