Experimental studies on Lecanora rupicola (L.) Zahlbr.: chemical and microscopical investigations of the mycobiont and re-synthesis stages

Abstract

Culture experiments that trigger the axenically grown mycobionts of Lecanora rupicola to produce the polyketide chemosyndrome typical of the naturally grown lichen are reported. This chemosyndrome comprises lecanoric, haematommic and orsellinic acids, sordidone, eugenitol and atranorin, all of which were hardly produced under standard culture conditions. The only exception was arthothelin that was only present in the voucher specimen. It has been shown that almost the complete acetyl-polymalonyl-pathway leading to depsides and chromones can be induced in culture, but apparently not the xanthones. The mycobiont was also successfully re-synthesized with its original photobiont, as confirmed by Scanning Electron Microscope studies (SEM). Cultures of the resynthesised lichen biosynthesized additional satellite substances, which were not detected either in the voucher specimens or in the aposymbiontically (without the photobiont) grown mycobiont cultures. The identity of cultured mycobionts of L. rupicola was confirmed by comparing ITS-DNA-sequence data from the original lichen with publicly available (GeneBank) sequences of that species.