A MARKED UPSHIFT IN THRESHOLD TEMPERATURE FOR THE S1-TO-S2 TRANSITION INDUCED BY LOW PH TREATMENT OF PS-II MEMBRANES

The temperature dependence of the S1-to-S2 transition in low-pH-treated PS II membranes was investigated by means of low-temperature EPR spectroscopy and thermoluminescence. (1) continuous illumination at -60°C (213 K) of low-pH-treated PS II induced neither the EPR multiline and g = 4.1 signals nor the thermoluminescence glow peak (B-band), but the same illumination at -5°C appreciably induced both EPR multiline signal and glow peak, although the multiline signal was modified in its fine structures and the g = 4.1 signal was largely suppressed. (2) Temperature dependence analysis by use of thermoluminescence revealed that the half-inhibition temperature for S1-to-S2 transition is markedly upshifted (by about 70°C) in low-pH-treated PS II. (3) The upshifted threshold temperature was returned to normal by the addition of exogenous Ca2+. These results are discussed in relation to the roles of Ca in S-state transition, and in comparison with the abnormal S2 state reported for Cl--depleted PS II. © 1990.