Use of a glass electrode for measuring rapid changes in photosynthetic rates

Reversible pH Changes in Cells of Chlamydomonas reinhardi Resulting from CO(2) Fixation in the Light and Its Evolution in the Dark

Illumination of a suspension of Chlamydomonas reinhardi causes an increase in the pH of the medium which is reversed in the dark. This pH change is a manifestation of CO(2) uptake in the light and its evolution in the dark. Simultaneous measurements of pH changes and oxygen evolution reveal that the photosynthetic coefficient approaches one.Intact cells of F-60, a mutant strain of C. reinhardi that lacks an active phosphoribulokinase, do not exhibit the light-dependent pH increase or oxygen evolution. However, chloroplast fragments prepared from the cells of the mutant strain exhibit a normal "proton pump" activity.The light-dependent pH increase shown by intact cells can be inhibited by KCN, by uncouplers of photosynthetic phosphorylation, and by Dio-9. It is markedly increased upon the addition of potassium bicarbonate, and all inhibitors tested inhibit the pH increase in both the presence and absence of potassium bicarbonate.The results of the present work negate the conclusion of other workers that the light-dependent pH changes in intact cells of C. reinhardi (and probably in other algae as well) are due to the operation of the "proton pump."

Gas exchange of algae. 3. Relation between the concentration of carbon dioxide in the nutrient medium and the oxygen production of Chlorella pyrenoidosa

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.