ESR Studies on Photosystem II samples aand Core Complexes from higher plants. Implications from studies on the g4.1 signal

Abstract

A protocol for the isolation and purification of Core Complexes from a higher plant Photosystem (PS) II preparation has been developed. Electron Spin Resonance (ESR) studies have shown these Core samples are capable of developing a multiline (ML) S2 state by low temperature illumination. Reillumination of Core samples poised in the ML S2 state at 145K using Far Red/ Near Infra-red (NIR) filtered light causes an S2 state interconversion, reducing the ML signal and developing the g4.1 signal. This interconversion has been observed in Core samples suspended in buffers containing sucrose, ethylene glycol (EG) and / or glycerol, with or without added ethanol for each buffer regime. For the illumination system used, such ML to g4.1 signal interconversion by NIR has been observed for PSII samples containing EG and / or glycerol only. Careful examinations and temperature dependence studies on the ESR spectra developed, indicate each of the ML and g4.1 signals are ground state signals. In the sucrose only Core samples, the g4.1 signal is observed in isolation, no other Mn or radical derived signals are observed to develop with increasing temperatures, confirming the result of Boussac and Rutherford (2000, BBA 1457, 145) for this sample regime. However, for samples containing EG and / or glycerol, an excited state radical signal is observed to develop overlying Signal II at higher temperatures. This is consistent with the signal behaviours previously reported and re-examined for PS II samples by this research group. Data is presented for the many buffer regimes examined and implications for the interaction of this radical with the OEC are discussed.