Topography of UV-melanized Thalli of Lobaria pulmonaria (L.) Hoffm.

Lichens are unique extremophilic organisms due to their phenomenal resistance to adverse environmental factors, including ultraviolet (UV) irradiation. Melanization plays a special role in the protection of lichens from UV-B stress. In present study, we analyzed the binding of melanins with the components of cell walls of mycobiont of upper cortex in the melanized lichen thalli Lobaria pulmonaria. Using scanning electron and atomic force microscopy, the morphological and nanomechanical characteristics of melanized layer of mycobiont cells were visualized. Melanization of lichen thalli led to the smoothing the surface relief and thickening mycobiont cell walls and resulted in the increase of deformation values and reduction of adhesion properties of lichen thallus. Treatment of thalli with hydrolytic enzymes, especially chitinase and lichenase, enhanced the yield of melanin from melanized thalli and release of carbohydrates, while treatment with pectinase increased the release of carbohydrates and phenols. Our results suggest that melanin by firmly binding with hyphal cell wall carbohydrates, particularly chitin and 1,4-β-glucans, can form associations, strengthen the melanized upper cortex of lichen thalli, and thereby can contribute to lichen survival under UV stress.