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) i n the lichen Evernia prunastri (L.) Ach. has been studied in laboratory con ditions. Freezing of lichen thalli produces solubilization of part of the p articulate enzyme from the cell wall of both mycobiont and phycobiont to th e corresponding cytoplasm. A supply of exogenous ribitol (naturally produce d by the algal partner) totally prevents the solubilization of the enzyme w hereas mannitol (naturally produced by the fungal partner) impedes the enzy me solubilization to a minor extent. RNase is preferably located in the phy cobiont cells in terms of specific activity. Ribitol also impedes the solub ilization of algal enzyme whereas mannitol strongly promotes the loss of RN ase from algal cell wall to the soluble fraction. Solubilization of fungal enzyme is enhanced by both polyols, with a preference for ribitol. (C) 2000 Editions scientifiques et medicales Elsevier SAS.