Metabolism of mycosporine-glutamicol in the lichen Cladonia arbuscula subsp. squarrosa under seasonal changes and elevated exposure to UV-B or PAR irradiation

Cladonia arbuscula in its environmental niches is regularly affected by daily and annual variations in solar radiation. Mycosporine-glutamicol, Myc-Glu(OH), which it synthesizes, may act as a significant cellular UV-protector. Therefore, we studied this compound concentration in lichen thalli concerning seasonal changes and increased exposure to UV-B and photosynthetically active radiation (PAR) with/without simultaneous $CO_{2}$ deprivation. Myc-Glu(OH) occurred year-round and exhibited a strong seasonality. The most crucial role in the control of its synthesis played UV-B radiation, although its high concentration was also found after PAR irradiation at 1000 mu mol $m^{-2} s^{-1}$. As PAR intensity increased to 2000 mu mol $m^{-2} s^{-1}$, the rate of Myc-Glu(OH) synthesis slowed down. In turn, under dark/PAR irradiation with simultaneous deprivation of $CO_{2}$ in the atmosphere surrounding C. arbuscula and during darkness with continuous access to atmospheric $CO_{2}$ , its production was insignificant. Obtained data confirmed that Myc-Glu(OH) plays an important role in protecting C. arbuscula from UV damage and favours its adaptation to environmental stress in its natural habitat. They also suggest that its synthesis is a synergism of multiple factors. Consequently, further studies should focus on their evaluation and the identification of a lichen partner actively involved in Myc-Glu(OH) biogenesis.