THE ORIGIN OF 115-130-DEGREES-C THERMOLUMINESCENCE BANDS IN CHLOROPHYLL-CONTAINING MATERIAL

High-temperature thermoluminescence (TL) emitted in the temperature re gion from +50 to +150 degrees C has been studied in a variety of chlor ophyll-containing samples that were allowed to dry during the TL measu rement. Analysis of the recorded traces by a multicomponent-fitting pr ocedure revealed the existence of up to three bands of nonphotosynthet ic origin with peak positions at 62-75, 114-128 and 151-157 degrees C and apparent activation energies of 27.0-28.8, 14.1-15.4 and 22.1-23.3 kcal/mol (the bands are denoted as HT1, HT2 and HT3, respectively), L ow-temperature treatment of leaves, incubation of algae in the presenc e of paraquat, exposure of algae or isolated thylakoids to a strong li ght, all conditions known to stimulate oxidative damage to membrane li pids, caused appearance of a small HT1 band and significant rise in th e intensity of the HT2 band. The increase in the HT2 component correla ted positively with accumulation of conjugated dienes and malondialdeh yde in thylakoids illuminated with a strong light. Different quenchers of active oxygen species and scavengers of free radicals added to pre illuminated thylakoids or thylakoid lipid extracts before the TL measu rements, as well as injection of argon into the TL measuring chamber, caused no changes in the intensity of the HT2 emission. The HT2 band i n the thylakoids increased strongly upon addition of linoleate peroxid ized by hydroxyradicals generated in the Fenton reaction but remained unchanged if the linoleate was oxidized with the use of lipoxygenase. We suggest that the HT2 band arises due to thermal decomposition of li pid cyclic peroxides present in the samples. In turn, the decompositio n reaction leads to formation of carbonyls in triplet state with follo wing migration of excitation energy toward chlorophyll, Contrary to th e HT1 and HT2 bands, the HT3 band of TL cannot be associated with the thermolysis of lipid peroxidation products already present in the samp les before starting the TL gradient.