Abstract_EANA2024-14

Abstract EANA2024-14

UV photo-degradation of the secondary lichen substance parietin: a spectroscopy analysis

Christian Lorenz (1,2), Elisabetta Bianchi (3), Andrew Alberini (2) Giovanni Poggiali (2,4), Renato Benesperi (3), Alessio Papini (3), John Robert Brucato (2)

(1) Department of Biology, University of Naples Federico II, Italy, (2) INAF-Astrophysical Observatory of Arcetri, Italy, (3) Department of Biology, University of Florence, Italy, (4) LESIA-Observatoire de Paris, France.

The cortical anthraquinone yellow-orange pigment parietin (also known as physcion) is a secondary substance found in various lichen species, offering UV protection [1, 2]. The secondary metabolite has been extracted from air-dried thalli of Xanthoria parietina Th. Fr., a widespread foliose lichen that grows on bark and rocks and demonstrates a broad tolerance to air pollutants such as NOX and heavy metals [3]. The objectives of this study were (i) to characterize parietin absorbance using UV-VIS spectrophotometry and IR spectroscopy, and (ii) to assess its photodegradability under UV radiation using in situ reflectance IR spectroscopy. This was done to understand the extent to which the substance protects the lichen's photobiont from UV rays. This relationship between parietin photodegradability and lichen UV tolerance in its natural terrestrial habitat and in extreme environments relevant to astrobiology was examined. The air-dried thalli were rinsed in acetone, and parietin crystals were recovered after the acetone evaporated [1]. The extracted crystals were UV irradiated for approximately 6 hours in an N2 atmosphere, and their photostability was measured at increasing intervals of irradiation using IR spectroscopy. After treatment, an upward shift in the continuum of the spectrum was observed, with specific degradations noted in the 3500 cm-1 (H2O and OH stretching) and 2930 cm-1 (-CH and =CH2 stretching) bands due to UV radiation. Considering the survivability of X. parietina in extreme conditions, such as space- and Mars-simulated environments [4], we emphasize the UV photo-resistance of parietin and its significance in astrobiology as a photo-protective substance and a potential biosignature.

References:

[1] Solhaug, K. A., & Gauslaa, Y. (1996). Parietin, a photoprotective secondary product of the lichen Xanthoria parietina. Oecologia, 108(3), 412-418.

[2] Solhaug, K. A., & Gauslaa, Y. (2004). Photosynthates stimulate the UV‐B induced fungal anthraquinone synthesis in the foliose lichen Xanthoria parietina. Plant, Cell & Environment, 27(2), 167-176.

[3] Silberstein, L., Siegel, B. Z., Siegel, S. M., Mukhtar, A., & Galun, M. (1996). Comparative studies on Xanthoria parietina, a pollution resistant lichen, and Ramalina duriaei, a sensitive species. I. Effects of air pollution on physiological processes. The Lichenologist, 28(4), 355-365.

[4] Lorenz, C., Bianchi, E., Benesperi, R., Loppi, S., Papini, A., Poggiali, G., & Brucato, J. R. (2022). Survival of Xanthoria parietina in simulated space conditions: vitality assessment and spectroscopic analysis. International Journal of Astrobiology, 1-17.