MONITORING ENERGY-CONVERSION IN PHOTOSYSTEM-I OF CYANOBACTERIAL HETEROCYSTS BY PHOTOACOUSTIC-SPECTROSCOPY

Photoacoustic spectroscopy was used to monitor photosynthetic energy storage in heterocysts isolated from the cyanobacterium Anabaena 7120. Three main energy-conversion pathways have been identified in these specialized cells: cyclic electron transport in photosystem I, nitrogen fixation, and respiration. The aim of this study was to define the conditions for estimating their interdependence. The gas phase (air, Ar, N//2, H//2) under which the sample was prepared or incubated, as well as the presence of electron donors (NADPH, NADH, H//2) and KCN (an inhibitor of respiration), determined the relative flux through the pathways. Heterocysts in which respiration and nitrogen fixation are inhibited have afforded a useful system for specific study of cyclic electron transport around photosystem I.