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UV-induced lability of lichen secondary compounds
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Dissertation
UV-induced lability of lichen secondary compounds
2000
Overview
This study tested the photolability of lichen products under different bands of ultraviolet (UV) light. Following various UV treatments in a growth chamber, analysis of chromatographically separated secondary compounds of Cladina uncialis through use of a transilluminator and gel documentation system showed higher levels of usnic acid were observed under UV-A and visible light in the absence of UV-B. The greatest concentrations were observed under the greatest flux. After treatment with high intensity UV-A/B from the transilluminator, compounds in acetone extracts of Cladina uncialis, C. rangiferina, Umbilicaria mammulata and Peltigera aphthosa were separated on thin-layer plates. Banding patterns of C. rangiferina, U. mammulata and P. aphthosa extracts were not altered by UV, but those of C. uncialis began to change after approximately 25 minutes of exposure. Intact thalli were also exposed to UV-A/B and phenolics extracted from these were qualitatively compared to UV-exposed isolated extracts. No visual differences in secondary products were observed in UV-exposed lichens suggesting phenolic integrity is better maintained within a thallus than in the isolated form. The effect of UV on usnic acid in intact thalli of C. uncialis was compared in killed and live thalli and the significantly lower concentrations found in dead material indicated that metabolic activity played a role in maintaining usnic acid levels. Comparisons of wet and dry samples revealed that hydrated thalli contained less usnic acid and suggested that degradation was more pronounced when the thallus was wet and perhaps more transparent to light. Lichen compounds are thus relatively stable under UV, but usnic acid is one compound that can be degraded by absorbing UV energy and thus may provide a degree of protection for the thallus.
Publisher
ProQuest Dissertations & Theses
Subject
ISBN
0612580148, 9780612580145
