Differential morphogenesis of the extraradical mycelium of an arbuscular mycorrhizal fungus grown monoxenically on spatially heterogeneous culture media

Abstract

A new in vitro experimental system was developed to study the morphogenesis of discrete regions of a single extraradical mycelium of the arbuscular mycorrhizal (AM) fungus Glomus intraradices, growing simultaneously in six different agar-based media. The media were (i) unamended water agar (WA), (ii) WA+PO43− (PO43−), (iii) WA+NO3− (NO3−), (iv) WA+NH4+ (NH4+), (v) WA+NH4++MES (NH4++MES) and (vi) minimal medium (M, complete nutrients). Each medium was amended with the pH indicator bromocresol purple. The extraradical mycelium of the fungus showed between-treatment differences in morphogenesis, architecture, formation of branched absorbing structures (BAS) and sporulation. Extraradical hyphae that developed in WA or PO43− compartments exhibited an economic development pattern, in which runner hyphae radially extended the external colony. Extraradical hyphal growth in the NO3− compartments was characterized by increased formation of runner hyphae, BAS and spores and an alkalinization of the medium. In the two NH4+-amended media (NH4+, NH4++MES), sporulation was suppressed and considerable morphological changes were noted. These results show the plasticity of G. intraradices that lets it efficiently exploit an heterogeneous substrate.