SYNTHESIS OF SECONDARY COMPOUNDS AS A UV-SCREENING STRATEGY OF LICHENIZED FUNGI FROM THE TROPICAL ANDES AND ITS POSSIBLE ROLE ON THE EARLY EARTH

Resumen

Photochemical analysis of secondary compounds in lichens from the Venezuelan Andean snow and glacier zones (4800-5000 m) was carried out in order to determine the absorbance capacity of UV radiation in the UVA, UVB and UVC ranges, and to characterize the probable UV-protective function. Spectrotometric (UV-VIS, NIR, FTIR, MS, NMR) and chromatographic (HPTLC) standardized techniques were utilized to identify the lichen compounds. UVB radiation in the glacier zone (5000 m) revealed a value of ~ 3 W m-2 which is sufficient to produce important biochemical and cell alterations. Of a total of 25 lichen species distributed in the glacier and snow zones, 68% showed the presence of phenolic compounds having strong absorption for UVC radiation, 96% had strong absorption for UVB radiation and 100% had strong absorption for UVA radiation. The substance groups that had the highest resistance to UVA and UVB radiation were characterized by ester bonds among both phenolic units (depsides). They were the most abundant products to be found among the lichens, whereas substances having ester and ether bonds in both phenolic units (depsidones) had a higher capacity to absorb UVC radiation. Microorganisms having adaptive UV-screening responses similar to the lichens investigated are expected to occur on the early Earth in O2 levels < 10-2.