Some Observations on Phosphate Metabolism in the Induction Phase of Photosynthesis in Chlorella

Orthophosphate decreases in Chlorella in the first minutes of illumination. At least two steps can be distinguished. The highest rate of phosphorylation is found immediately at the onset of illumination. This phase is completed in at most 10 seconds. Both labile and stable compounds are formed. This phase is independent of COa, and is saturated at low light intensity (about 5 times compensation). It may reflect, at least partly, the light phosphorylation proper, and is probably limited by the available amount of acceptor. In the second phase, stable phosphates are formed. The rate depends on light intensity and carbon dioxide. This phase is thought to represent the accumulation of products of photosynthesis. The first and second phase are sometimes separated by a lag period of about 10 seconds. DNP is inhibitory at low light intensity only. This is similar to its influence on photosynthesis. Sigmoid rate intensity curves are found in both cases. It is concluded that photosynthetic phosphorylation is especially significant at low light intensities.