[The formation of polyphosphates in ankistrodesmus braunii by photophosphorylation in red and in far-red light under nitrogen]

Abstract

A simplified extraction procedure was used to study the effect of red and far-red light (683 and 712 nm) on the incorporation of (32)P and on the distribution pattern of various phosphate fractions in 8 min-experiments under nitrogen. Nitrogen was used to avoid competition for energy-rich phosphate bonds between CO2-fixation and the formation of polyphosphates. The total incorporation of (32)P was higher in red than in far-red light, and so was the percentage of the acidsoluble organic phosphate. In the absence of oxygen the incorporation in the dark was rather low and mainly confined to orthophosphate. The ratio between the amount of labelling of polyphosphates and that of acid-soluble organic phosphates was higher in far-red light and in the dark than in red light.DCMU, even in a nitrogen atmosphere, produced a servre inhibition in red light. This inhibition increased with increasing light intensity. The labelling of organic phosphates was more affected than that of polyphosphates, while orthophosphate incorporation was least inhibited. In far-red light, DCMU exerted little influence except at a rather high light intensity, showing that cyclic photophosphorylation was proceeding alone.Antimycin A, on the other hand, was almost ineffective in strong red light, but produced a serious inhibition in far-red light. In red light of medium intensity, antimycin effected some inhibition, although much less than DCMU. Under these conditions the effect of the two inhibitors was additive when they were applied together. Labelling of polyphosphates was more sensitive to antimycin A than labelling of acid-soluble organic phosphates.It may be concluded from the data presented that far-red light produces conditions for pure cyclic photophosphorylation, whereas a large proportion of the photophosphorylation taking place in red light in the absence of CO2 and exogenous oxygen might be regarded as "pseudocyclic". The distribution pattern of the phosphorylated fractions under the different conditions suggests that polyphosphate formation in the light is favoured but not exclusively effected by cyclic photophosphorylation.