THE 75-DEGREES-C THERMOLUMINESCENCE BAND OF GREEN TISSUES - CHEMILUMINESCENCE FROM MEMBRANE-CHLOROPHYLL INTERACTION

Exposure of thylakoid membranes of green plants to high temperature pr omotes the appearance of free radicals resulting in a thermoluminescen ce (TL) band peaking around 75-degrees-C. The occurrence of this band with the same intensity in preilluminated and in dark-adapted samples demonstrates that, contrary to several other TL bands, it is not a res ult of charge recombination. The high temperature TL band is oxygen de pendent. Parallel to TL emission singlet oxygen is formed, as demonstr ated by spin trapping EPR measurements and by the decrease of TL inten sity in the presence of sodium-azide, a singlet oxygen scavenger. We s uggest that the 75-degrees-C TL band is a result of a temperature-enha nced interaction between molecular oxygen and the photosynthetic membr ane, possibly involving lipid peroxidation. The spectral maximum of th e emission (around 720 nm) implies thai light emission occurs upon ene rgy transfer from an excited product to chlorophyll molecules destabli zed from pigment-protein complexes.