Morphological, Physiological, and Biochemical Traits of Melanized Thallus of the Cetraria islandica Lichen

Abstract

Lichens are extremophilic symbiotic associations possessing phenomenal resistance to abiotic stress-factors. In this regard, melanization of thalli in response to UV is one of the mechanisms protecting lichens from excessive insolation. However, microstructure and biochemical properties of the melanized thalli are still poorly investigated. In the present study, morphological, nanomechanical, and physiological, and biochemical traits of naturally melanized thalli of the Cetraria islandica (L.) Ach. lichen were examined. In the upper cortex of its thallus, the nature of the pigment layer was verified using typical qualitative reactions for melanins. It was found that melanization leads to changes in microstructure of the upper cortex of the mycobiont, in particular, thickening of the cell walls and extension of the interhyphal space. The melanized and pale (nonmelanized) thalli were found to differ from each other in their nanomechanical properties, including the parameters of adhesion and rigidity. This implies the possible formation of complex associates of melanin with cell wall components in the melanized mycobiont. In addition, higher antioxidant activity and lower respiratory activity were found in the melanized thalli of C. islandica in comparison with the pale thalli. Presumably, the found modifications in the microstructure and nanomechanical, physiological, and biochemical properties of thalli occurring in the course of melanization make lichens more resistant to intense insolation.