| Summary: | In this study, we investigated the effects of low temperature on the fast chlorophyll fluo-rescence transient (OJIP) and OJIP-derived parameters in chlorolichen Dermatocarpon polyphyllizum expossed to a gradually decreasing temperature (22°C, 18°C, 14°C, 12°C, 10°C, 7°C and 4°C). The segments of lichen thalli were exposed to a certain temperature either in dark- and light-adapted state for 10 minutes in order to evaluate the effects on chlorophyll fluorescence parameters. The initial photochemical phase of the transient (O-J) due to reduction of the primary quinone acceptor (QA) was found temperature dependent. The K-step was apparent for the samples measured at the temperature above 12°C, but not below 10oC in light-adapted lichen thalli. With the thallus temperature decrease, majority of the chlorophyll fluorescence parameters derived from OJIP (ET0/RC, Psi_0, and DI0/RC) showed no change in light-adapted samples but a decrease in dark-adapted samples. The effects of dark- / light-adaptation of the lichen samples on the OJIP and OJIP-derived parameters was attributed to the differences in production/utilization of high-energy products of primary photochemical processes of photosynthesis in dark- and light-adapted state, respectively. The other parameters (ABS/RC, TR0/RC) showed a decrease with thallus temperature decrease both in light- and dark-adapted samples. The results suggest that fast chlorophyll fluorescence trasient is an useful tool to investigate temperature-dependent changes in photosystem II in chlorolichens, their photobionts, respectively.
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