Effect of complete extraction and re-addition of managanese on thermoluminescence of pea Photosystem II preparations

Abstract

Thermoluminescence of Photosystem II particles isolated from pea chloroplasts using digitonin and Triton X-100 was measured after 1 min illumination at a certain temperature ( T ex) followed by illumination during cooling (40 Cdeg/min) to a lower temperature. Glow curves of the particles are characteristic of the photosynthetic oxygen-evolving material studied earlier. Complete (more than 95%) removal of Mn from the Photosystem II particles abolishes thermoluminescence bands around 0°C, related to the oxygen-evolving system, but the thermoluminescence bands peaking around −30°C (TL −30), −55°C (TL −55) and between −68 and −85°C, depending on T ex(TL v), remain unaltered. The bands are characterized by different dependence on T ex. The TL −30, TL −55 and TL v bands can also be observed in the glow curve of isolated pea and spinach chloroplasts. Re-addition of MnCl 2 (2 μM, corresponding to nearly 4 Mn atoms per reaction center of Photosystem II) to the Mn-depleted particles does not reactivate the thermoluminescence bands around 0°C. However, it does lead to suppression of TL −30 accompanied by parallel activation of TL −55, revealing competition of the TL −30 and TL −55 for charges generated by the reaction center. These data, as well as the results on the effect of inhibitors and electron donors to Photosystem II, show that positive charges contributing to the TL −30, TL −55 and TL v thermoluminescence bands are located on secondary electron donors of Photosystem II which do not require Mn and are located closer to the reaction center than the Mn-containing, water-oxidizing enzyme.