C₄-Weg der Photosynthese in der Blaualge Anacystis nidulans

Summary

CO₂ exchange, ¹⁴CO₂ fixation and radioactive photosynthetic products of Anacystis nidulans (strain L 1402-1) were studied during the induction period at +30° C. The algae were grown at +35° C in an atmosphere of 0.03 or 3.0 vol.-% CO₂ and were measured under conditions of low CO₂ concentrations. At the beginning of the photosynthetic period ¹⁴CO₂ was mainly incorporated into aspartate and glutamate. The patterns of labelling are very similar to those of the C₄ pathway of photosynthesis. α-Hydroxypyridylmethane-sulfonic acid (10^-5 M) and isonicotinyl hydrazide (10^-2 M) have only a small effect on the percentage distribution of labelled products. The activities of glycolate dehydrogenase, ribulose-1,5-diphosphate carboxylase and phosphoenolpyruvate carboxylase, measured in crude extracts of Anacystis, were inhibited by α-hydroxypyridylmethane-sulfonic acid and dichlorophenyldimethyl urea.

In other series of experiments the pattern of ¹⁴C incorporation from asparate was investigated. Radioactivity from [¹⁴C]aspartate was mainly incorporated into glutamate, alanine, theronine, isoleucine and glycine/serine. Enzyme activities of citrate synthase, aconitate hydratase, isocitrate dehydrogenase and glutamate dehydrogenase were relatively low in CO₂-grown Anacystis cells compared to those in air grown cells. The obtained results are discussed, with reference to the operation of the C₄ pathway of photosynthesis and reductive carboxylation of succinate to glutamate in Anacystis.