Jansen, M.A.K., Department of Plant Genetics, Weizmann Institute of Science, Rehovot, Israel, Department of Plant Physiology, Wageningen Agricultural University, Wageningen, Netherlands, Department of Plant Physiology, Wageningen Agricultural University, Arboretumlaan 4, 6703BD Wageningen, Netherlands
Greenberg, B.M., Department of Biology, University of Waterloo, Waterloo, Ont., Canada
Edelman, M., Department of Plant Genetics, Weizmann Institute of Science, Rehovot, Israel
Mattoo, A.K., Plant Molecular Biology Laboratory, USDA/ARS, Beltsville Agric. Research Center, Beltsville, MD, United States
Gaba, V., Department of Virology, ARO Volcani Center, Bet Dagan, Israel

The D2 protein of photosystem II is relatively stable in vivo under photosynthetic active radiation, but its degradation accelerates under UVB radiation. Little is known about accelerated D2 protein degradation. We characterized wavelength dependence and sensitivity toward photosystem II inhibitors. The in vivo D2 degradation spectrum resembles the pattern for the rapidly turning over D1 protein of photosystem II, with rates being maximal in the UVB region. We propose that D2 degradation, like D1 degradation, is activated by distinct photosensitizers in the UVB and visible regions of the spectrum. In both wavelength regions, photosystem II inhibitors that are known to be targeted to the D1 protein affect D2 degradation. This suggests that degradation of the two proteins is coupled, D2 degradation being influenced by events occurring at the QB niche on the D1 protein.