Application of in vitro methods to study carbon uptake and transport by AMfungi

Just as multi-compartmented root chambers have advantages over standard pla stic pots for the study of nutrient uptake by arbuscular mycorrhizal [AM] f ungi in soil, so the split-plate in vitro system has advantages over the st andard dual culture system for the study of the physiology of AM fungi. We used the split-plate culture system of Ri T-DNA transformed Daucus carota L . roots and Glomus intraradices Schenck & Smith, in which only the fungus h as access to the distal compartment, to study the ability of germ tubes and extraradical and intraradical hyphae to take up C-13-labeled substrates. L abeled substrates were added to one side of the plate divider and plates we re incubated for 8 weeks while the fungus proliferated on the side from whi ch the root was excluded. Tissues then were recovered from the plate and ex amined via NMR spectroscopy. Results showed that the morphological phases o f the fungus differed in their ability to take up these substrates, most no tably that intraradical hyphae take up hexose while extraradical hyphae can not. In addition, NMR studies indicated that intraradical hyphae actively s ynthesized lipids while extraradical hyphae did not. These data show that e ventual axenic culture of AM fungi is more than a matter of finding the pro per substrate for growth. Genetic regulation must be overcome to make extra radical hyphae behave like intraradical hyphae in terms of C uptake and met abolism.