OBSERVATIONS OF CHEMICALLY-INDUCED DYNAMIC ELECTRON POLARIZATION IN PHOTOSYSTEM-I OF GREEN PLANTS AND ALGAE

Flash photolysis experiments with electron paramagnetic resonance detection were carried out between 10 and 300 K on samples of green plant and whole algal species. Chemically induced dynamic electron polarization (CIDEP) was evident for the transient signals observed at low temperatures in the g = 2.0 region for 100-kHz and 2-MHz modulated detection as well as for a direct detection system with no magnetic field modulation. The light reversible signals decaying in about 0.6 ms are interpreted as arising from photosystem I of the green plant and algal samples. These transient signals exhibited orientation-dependent differences when samples of whole chloroplasts or whole algal cells were oriented in a strong magnetic field (2.4 T) and then frozen at 77 K. The algal species included both normal and ∼97% deuterated Scenedesmus obliquus and normal Anacystis nidulans. These results are considered in terms of the information which they reveal concerning the identity of the electron acceptors of photosystem I. © 1979 American Chemical Society.