Characterization of the diversity of mycosporine-like amino acids in lichens from high altitude region of Himalaya

Lichens are tolerant to a number of environmental variables including high-intensity solar radiations, which is mainly due to the presence of chemical substances in the thallus. Especially, cyanobacterial lichens synthesize a unique class of chemical substances known as mycosporine-like amino acids (MAAs) the primary characteristic of which is strong ultraviolet (UV) absorption between 300 and 360 nm. In view of its UV-protecting potential, the applicability of mass spectral fragmentation using electrospray ionization tandem mass spectrometric analysis for the characterization of MAAs in lichen samples was explored. MAA compounds were characterized in four cyanobacteria-containing lichen species belonging to genus Peltigera, Stereocaulon and Lobaria. Among them, Peltigera and Lobaria are true cyanobacteria containing lichens (cyanolichens) while Stereocaulon is a tripartite lichen, as it contains both green algae (in the thallus) and cyanobacteria (in the cephalodia), collected from higher altitudes of Himalaya (Tungnath-Chopta in Garhwal Himalaya, 3432 m) from an exposed locality experiencing high light intensity. Mass spectral data of distinctive fragmentation pattern revealed that all the four species have good diversity of MAA compounds, especially Lobaria retigera was found to be enriched with highest diversity of oxo and imino MAAs. Overall, different numbers of oxo and imino MAA compounds were detected in the remaining lichen species. Good diversity of imino MAAs has ecological significance which is required to be investigated further. Moreover, the impressive diversity characterized in each lichen species suggests that lichens should be thoroughly studied for their MAAs contents.