The changes in thermoluminescence (TL) signals induced by short-term ozone exposure of leaves are characterized by a down-shift of the peak-temperature of the TL B-band and an increase of a TL band at 55 °C. We investigated the relationship of these changes to photosystem 2 (PS2) photochemistry. The changes were not only detectable in the presence of ozone, but also after irradiation of dark-adapted leaves and after aging of irradiated detached leaf segments. The opposite effect on TL, an up-shift of the peak-temperature of the B-band and the decrease of the intensity of the band at 55 °C were found after infiltration of leaves with nigericin, antimycin A, and diphenyleneiodonium chloride (DPI). Propyl gallate down-shifted the peak-temperature of the B-band. 2,5-dimethyl-1,4-benzoquinone up-shifted the peaktemperature of the B-band and decreased the intensity of the 55 °C band. The intensity of the 55 °C band did not change significantly in the presence of oxygen in comparison to that in nitrogen atmosphere. It decreased with time of dark adaptation (50 % intensity was observed after 3 h of dark adaptation at room temperature), however, it was reactivated to its initial value (at 5 min of dark adaptation) after 1 single-turnover flash. The 55 °C band was not significantly changed in the presence of DCMU. Thus the ozone-induced band at 55 °C is assigned to charge recombination in PS2. Changes in the electron transport chain at the acceptor side of PS2, probably related to the cyclic electron transport around photosystem 1 and/or chlororespiration, could play an important role in the increase of the 55 °C band and the down-shift of the B-band. The changes at the acceptor side indicated by TL can be an expression of a physiological regulatory mechanism functional under stress conditions.
The effect of different UV intensities and irradiation times on barley and tomato leaves was investigated by analysis of thermoluminescence (TL) and chlorophyll (chl) fluorescence measurements. Epifluorescence microscopy was used to estimate the epidermal UV transmittance of leaves. In barley a strong supression of TL emission from the S 2 Q B − (B-band) and the S 2 Q A − (Q-band) charge recombination was observed, increasing with prolonged UV exposure. Primary barley leaves were more sensitive to UV than secondary leaves. In tomato plants a decrease in the B-band only takes place at very high UV intensities and after prolonged exposure times (4 h). The impact of UV in cotyledons was more pronounced than in pinnate leaves of tomato plants. The strong differences in sensitivity to UV in the investigated barley and tomato variety may be due to different concentrations of UV screening pigments in the epidermal layer as demonstrated by epifluorescence measurements. The results show that TL has the same potential to analyse the sensitivity or tolerance of crop plants to UV irradiation as routine fluorescence techniques. Furthermore, TL is directly monitoring the radical pair states of PSII and can distinguish between UV-induced donor and acceptor site-related damage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.