The cryoprotective role of polyols in lichens: Effects on the redistribution of RNase in Evernia prunastri thallus during freezing

The effect of low temperatures on the distribution of RNase (EC 3.1.26.1) in the lichen Evernia prunastri (L.) Ach. has been studied in laboratory conditions. Freezing of lichen thalli produces solubilization of part of the particulate enzyme from the cell wall of both mycobiont and phycobiont to the corresponding cytoplasm. A supply of exogenous ribitol (naturally produced by the algal partner) totally prevents the solubilization of the enzyme whereas mannitol (naturally produced by the fungal partner) impedes the enzyme solubilization to a minor extent. RNase is preferably located in the phycobiont cells in terms of specific activity. Ribitol also impedes the solubilization of algal enzyme whereas mannitol strongly promotes the loss of RNase from algal cell wall to the soluble fraction. Solubilization of fungal enzyme is enhanced by both polyols, with a preference for ribitol.