Photosynthetic energy conservation investigated by thermoluminescence. Activation energies and half-lives of thermoluminescence bands of chloroplasts determined by mathematical resolution of glow curves.

Thermoluminescence of isolated chloroplasts was analysed by a computer-assisted multicomponent curve fitting procedure to determine the activation energies, the free energies of activation, frequency factors and half-lives of the component bands of the glow curve. Optimal fit was obtained in the temperature region from -80 degrees C to +80 degrees C by the resolution of the glow curve into seven bands with peak positions at -24, -12, +12, +17, +28, +44, and +69 degrees C. All of the activation free energies of the thermoluminescence bands were much higher than 0.59 eV, the minimum free energy of activation required for the back reaction of the primary charge separation as calculated on the basis of the theory of Ross and Calvin (Ross, R.T. and Calvin, M. (1967) Biophys. J. 7, 595-614). The high free energies of activation and long half-lives (longer than 50 ms) of the thermoluminescence bands suggest that thermoluminescence in the temperature region from -80 degrees C to 80+ C does not reflect the change recombination of primary products but represent the reversal of subsequent stabilization steps of the charge separation process which proceed along the acceptor and donor sides of Photosystem II.