Morphogenetic strategies and induction of secondary metabolite biosynthesis in cultured lichen-forming Ascomycota, as exemplified by Cladia retipora (Labill.) Nyl. and Dactylina arctica (Richards) Nyl.

Over the last ten years a considerable number of lichen fungi (200 voucher specimens and their corresponding mycobionts) have been cultured and screened for the formation of secondary compounds (lichen substances). The production of lichen polyketides was found to be strongly affected by the composition of the nutrient media, dominant environmental parameters in the micro-habitat, and also by morphogenesis and cell differentiation of the mycelia. The present investigation deals with two lichens exhibiting very complex and unusual growth forms. The Australasian lichen Cladia retipora is one of the more fascinating fruticose lichens given its capacity to form very complex net-like structures (fenestrations). The North American and Asian lichen Dactylina arctica forms finger-like stalks which are well adapted to the harsh climatic conditions of arctic habitats. Cultures of both lichens and their corresponding mycobionts were found to exhibit exceptional morphogenetic strategies and capacities during their development and a well determined pattern (physiological and chronological) for producing typical secondary chemistry. In a re-synthesis and re-lichenization experiment (after culturing for 2 years) complete thalli containing the typical lichen substances were formed in vitro.