Study on The Reversible Heat-Inactivation at 45oC of O2-evolvng System of Cl- Requiring Chloroplasts and Protection of The Chloroplasts from The Heat-Inactivation by adding Cl- and Ca2+ ions

Abstract

As reported in last year, O₂-evolving system of spinach chloroplasts could reversibly be heat-inactivated at 50^oC and restored the activity by photo-reactivation. Next, further lower temp at 45^oC was expected for the reversible heat-inactivation as D.Nash, M.Miyao and N.Murata (Biochim. Biophys. Acta vol-807 (1985) 127-133) reported that Cl^- ion requiring PSII-particles was heat-inactivated at 45^oC. So, in this study, Cl^- requiring chloroplasts were prepared by washing them with hypotonic Cl^- ion free solution and successfully heat-inactivated the chloroplasts at 45^oC which were reversibly photo-reactivated to restore the O₂ evolving activity. The site of reversible heat-inactivation was determined to be at PSII by measuring the light-induced chlorophyll fluorescence rise (Fv-Fo) and O₂-evolving Hiil reaction. The chloroplasts could be protected from the heat-inactivation by adding Cl^- and Ca²⁺ ions.