The effect of the low temperature acclimation and photoinhibitory treatment on photosystem 2 (PS 2) of the cold-unhardened and -hardened spinách leaves were studied by thermoluminescence emission. Acclimation as well as photoinhibition at 4 °C rose inactive PS 2 reaction centres which did not produce thermoluminescence.
Energy-dependent quenching of chlorophyll fluorescence and its reversion in intact isolated spinách chloroplasts were recorded at temperatures between 0 and 20 ®C. A temperature-dependence of Ihe quenching formation (and of quenching relaxation) corresponding to Qio values between 2 and 3 was found. Long-term cold acclimation of the plants resulted in a decrease of die fluorescence dechne half-time. The finál steady-state extent of quenching (q^) was not influenced by temperature shifts or cold acclimation.
Immunological quantification of the thylakoid membranes Dl protein showed that in intact leaves of spinách and intact mesophyli protoplasts of Valerianella locusta L. photoinactivation of photosystem 2 was not related to the net degradation of Dl. The data indicate a sync^onization between the Dl degradation and resynthesis during photoinhibition and recovery in vivo.