Leaf discs of dark-adapted tobacco plants were excited by 2 flashes and kept in darkness at 20 °C for various time periods, then thermoluminescence emission was recorded without freezing the sample. The B band at 30 °C decreased with a half-time t 1/2~1 min and the AG band at 45 °C with a t 1/2~5 min. This corresponds to the decay kinetics of S2/3 in PS II centres in the state S2/3 Q B - (B band) or S2/3 Q B . Assuming that the 45 °C band is an ‘afterglow’ emission originating from those centres with an oxidized Q B on which an electron is back-transferred from stroma reductants through a pathway induced by warming, the theoretical ratio of the B and AG band was compared to that measured experimentally. After 2 or 3 flashes producing mainly S3, the intensity of AG band encompassed several fold that of the B band, because recombining S3 recreated S2 Q B AG-emitting centres. In order to confirm that the AG band is governed by the heat-induced activation of a dark Q B -reducing pathway rather than by PS II charge recombination, the AG emission was characterized in triazine-resistant Chenopodium album weed biotypes. In these mutants where the Q B pocket is altered, the B band is strongly downshifted to 18 °C, compared to 32 °C in the wild type, whereas the AG band is only downshifted by 3 or 4 °C, demonstrating that S2/3 Q B - is not the limiting step of the AG emission.