The Effect of pH on the Products of Photosynthesis in ¹⁴CO₂ by Chloroplast Preparations from Acetabularia mediterranea

Abstract

The effect of pH on the pathways of carbon in photosynthesis was examined in chloroplast preparations from Acetabularia mediterranea. The flow of carbon into a number of photosynthetic intermediates, particularly sucrose, glycine, serine, glycolate, and the insoluble fraction, was strongly influenced by pH. At higher pH a much larger portion of the SC entered intermediates of the glycolate pathway. Although maximal apparent photosynthesis occurred at pH 7.6 to 7.7, cytoplasmic pH was found to be 8.0 to 8.4, using indicators. The pattern of distribution of "C in intermediates of whole cells was closest to that in chloroplasts at the higher pH range.A number of studies have established the pH for the maximal rate of carbon fixation in cells (15) and in isolated chloroplasts (7, 9, 10). Early experiments of Calvin et al. (6) (14), using Chlorella and Scenedesmus, found substantially higher incorporation of CO, into serine, glycine, and glycolate at pH 8.8 than at pH 7.0.We are not aware, however, of any studies showing the effect of pH on either the intermediates of photosynthesis or the pathway of carbon in isolated chloroplasts. Preliminary work in this laboratory with chloroplast preparations from Acetabularia mediterranea suggested that pH affects the pattern of photosynthetic incorporation of "C into most intermediates of the glycolate pathway and the photosynthetic carbon reduction cycle (F. Winkenbach and R. G. S. Bidwell, unpublished). This paper describes the results of an investigation of the effect of pH on the incorporation of 'CO, into photosynthetic intermediates in these chloroplast preparations.I The authors wish to acknowledge financial assistance from the National Research Council of Canada.'Present address:

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