Cryoproective role of ribitol in Xanthoparmelia somloensis

Thalli of Xanthoparmelia somloensis with natural content of polyols (control) and polyol-free thalli (acetone-rinsed) were used to study ribitol effects at low temperatures. Thalli segments were cultivated in ribitol concentration of 32 or 50 mM for 168 h at temperatures +5, 0, and −5 °C. The chlorophyll fluorescence parameters (potential yield of photochemical reactions in PS 2 (variable to maximum fluorescence ratio, Fv/Fm), effective quantum yield of photochemical reactions in PS 2 (ΦPS₂), and non-photochemical quenching (NPQ) were monitored in 24-h intervals using an imaging system. The effect of 32 mM ribitol on Fv/Fm and ΦPS₂ was apparent only at −5 °C, however, the effect was seen throughout the whole exposure. Surprisingly, 50 mM ribitol concentration treatment led to a decrease in Fv/Fm and ΦPS₂ and to an increase in NPQ values at −5 °C, while no change was observed at 0 °C and +5 °C. Acetone-rinsing caused decrease of Fv/Fm, ΦPS₂ and NPQ.