Photosynthetic electron transport at low temperatures in the green algal foliose lichens Lasallia pustulata and Umbilicaria hirsuta affected by manipulated levels of ribitol

In lichens, ribitol is known as a carbon storage compound, an osmotic agens involved effectively in cell compartments protection during dehydration of lichen thalli and as a cryoprotective compound. In our study, we investigated the effect of ribitol on photochemical processes of photosynthesis in foliose lichens [Lasallia pustulata (L.) M,rat., Umbilicaria hirsuta (Sw. ex Westr.) Hoffm.] at low temperature. The effects of three concentrations of ribitol, added externally to thalli segments on several chlorophyll (Chl) fluorescence parameters, were evaluated. The 72 h exposition to 8, 16, and 26 mM ribitol led to a concentration-dependent increase in F-V/F-M, decrease in non-photochemical quenching (NPQ) but no change in quantum yield of photosystem II photochemistry (I broken vertical bar(PSII)) values at -5 A degrees C). At higher temperature (0, +5 A degrees C), no effect of ribitol addition on the photosynthetic parameters was apparent.