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 the present study, we analyzed the binding of melanins with the components of cell walls of the mycobiont of the upper cortex in the melanized lichen thalli Lobaria pulmonaria. Using scanning electron and atomic force microscopy, the morphological and nanomechanical characteristics of the melanized layer of mycobiont cells were visualized. Melanization of lichen thalli led to the smoothing of the surface relief and thickening of mycobiont cell walls, as well as the reduction in adhesion properties of the lichen thallus. Treatment of thalli with hydrolytic enzymes, especially chitinase and lichenase, enhanced the yield of melanin from melanized thalli and promoted the release of carbohydrates, while treatment with pectinase increased the release of carbohydrates and phenols. Our results suggest that melanin can firmly bind with hyphal cell wall carbohydrates, particularly chitin and 1,4-& beta;-glucans, strengthening the melanized upper cortex of lichen thalli, and thereby it can contribute to lichen survival under UV stress.

Automated summary

Lichens are extremophilic organisms with exceptional resistance to environmental factors, including UV irradiation. Melanization, through its binding with cell wall components, plays a crucial role in protecting lichens from UV-B stress. Our study found that melanin can bind with carbohydrates in the hyphal cell wall, particularly chitin and 1,4-β-glucans, resulting in the smoothing of the surface relief and thickening of cell walls in the melanized upper cortex of lichen thalli, which contribute to their survival under UV stress.