Multitasking UV-absorbing compounds of Chorisodontium aciphyllum

Chorisodontium aciphyllum is a hardy terrestrial plant found living in Maritime Antarctica, one of the harshest environments on Earth. Elevated temperatures, stronger winds, and increased ultraviolet-B radiation are some of the conditions that C. aciphyllum is exposed to due to the changing climate. Ultraviolet (UV) radiation-absorbing compounds are produced within this species and so contribute to its resilience. C. aciphyllum grows to form long shoots of moss, therefore these compounds have the potential to serve as environmental proxies as the concentration fluctuations down a shoot may provide information on past climate conditions. This study aimed to begin characterisation of the UV-absorbing compounds of C. aciphyllum sampled from the South Shetland Islands region, Maritime Antarctica, and to examine concentration fluctuations down long shoots. This was achieved by extracting those housed intracellularly and in the cell wall using acidified methanol and alkali based solvents, respectively. Separation and preliminary characterisation were performed using ultra-high performance liquid chromatography and liquid chromatography-mass spectrometry. The eleven compounds extracted from the intracellular matrix were different between metabolically active and inactive tissue, while ten cell wall compounds were found in both tissue types. Cell wall compounds absorbed more strongly in the UV-B radiation range, suggesting they have a primary role in UV-B screening while intracellular compounds have strong antioxidant activity, indicating they may have other functions. The UV-absorption and mass spectra of three cell wall compounds were suggestive of hydroxycinnamic acids, while two intracellular compounds were possibly biflavonoid isomers. These flavonoid compounds may degrade in certain storage conditions and leach out of cells over time, thereby being strongly influenced by environmental stressors. Compound analysis down moss shoots, two of which have previously been radiocarbon dated, revealed that intracellular and cell wall compounds varied in concentration down the shoot. Therefore, elucidation of the structures of these valuable UV-absorbing compounds as well as the environmental drivers that induce them, could lead to their usefulness as proxies for past climate conditions of Maritime Antarctica, including elevated UV-B radiation. Cell wall compounds were proposed to be more suited to this purpose due to their stability and remaining tightly bound to the cellulose along moss shoots.