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Introduction: Polyols (sugar alcohols) help lichens to maintain physiological activity at sub-zero temperatures. Among them, ribitol synthetised by symbiotic green algae in a lichen thallus represents one of the most important. Ribitol is main high-energy compound exported from a symbiotic producer (alga) to a consumer (fungus) and its natural concentration in a lichen thallus ranges 2-7 µg g-1 DM [1,2]. In fungal hyphae, ribitol is transformed into mannitol, which serves as energy source for maintenance and growth of fungal hyphae as well as production of fungal-specific compounds [3], such as e.g. pigments [4]. Limited number of experiments has been made so far, that focused on cryoprotective effects of ribitol on physiological processes of symbiotic algal cells [e.g. 5]. Here, some preliminary results are presented for two lichen species exposed to 3 stepwise increased concentrations of ribitol. Material and Methods: Thalli of foliose lichen species Umbilicaria hirsuta, Lasallia pustulata were collected from granitic rocks in the valley of the Chvojnice river in a close vicinity of Ketkovice, 35 km W of Brno. From fresh thalli, circular segments (1.5 cm2) were cut. Two hours before expostion to low temperature, the segments were treated with 3 different concentrations of ribitol under room temperature. Then, the segments with individual ribitol concentrations were put at temperature gradient cultivator and exposed to four temperatures (-15, -5, +5, +22 oC) for 3 d at low light. Before exposition, and then in 24 h interval, chlorophyll (Chl) fluorescence parameters of the segments were measured using a kinetic fluorometric CCD camera (HFC-010, PSI, Czech Republic). For each segment, potential quantum yield of photochemical processes in photosystem II (FV/FM), effective quantum yield of PS II (II), and Chl fluorescence quenching parametres were evaluated. The effect of ribitol on the Chl fluorescence parameters was expressed as a change against control (demineralized water, no addition of ribitol). Results and Discussion: Preliminary results showed that effect of polyols on PS II functioning is apparent in low temperature only when high concentrations are used. The question arises what is the effective concentration of polyols in thalli under natural conditions. Few improvements of the above described methods and some additional analyses are required to answed the question and evaluate the role of polyols in low temperature resistance in lichen thalli under the field conditions. References: [1] Armstrong R.A., Smith S.N. (1994): Env. Exp. Bot. 34: 253-260 [2] Dahlman L., Persson J.(2003): Planta 217: 41-48. [3] Palmqvist K. (2000): New Phytol. 148: 11-36. [4] Solhaug K.-A., Gauslaa Y. (2004): Plant, Cell Environ. 27: 167-176. [5] Fontaniella B., Vicente C., Legaz M.-E. (2000): Plant Physiol. Biochem. 38: 621-627. Acknowledgements: The research was supported by the GAČR project 206/03/P140.
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