Author
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Nagahashi, Gerald |
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Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/20/2004 Publication Date: 9/30/2004 Citation: Nagahashi, G. 2004. Isoldated root caps, border cells and mucilage from host roots stimulate hyphal branching of the arbuscular mycorrhizal fungus, gigaspora gigantea. Mycological Research. 180. p. 1079-1088. Interpretive Summary: Most land plants, including agricultural crops, can be infected with a helper fungus. The fungus is more efficient in its ability to extract minerals from the soil than the host plant and thereby provides nutrients to a plant growing in poor quality soil. The fungus receives sugar from the plant as part of this mutual exchange process. To provide a fungal inoculum for poor soils, it is necessary to unravel the steps of the fungal life cycle. It is known that the fungus is attracted to compounds which are secreted into the soil by the root tips of a host plant. However, it is not known why the fungus can recognize and infect the root at distances far removed from the tip. The results reported here clearly show that root caps, root slime (mucilage), and cells from root caps (termed border cells) can adhere to roots along the length of the whole root. This fact, coupled with the results that root caps and mucilage both carry compounds that stimulate fungal growth, have explained clearly how a root can be infected anywhere along the length of its axis. Technical Abstract: Unlike all previous reports that have shown that water soluble and volatile compounds from roots or root exudates play a major role in precolonization events during arbuscular mycorrhizal (AM) fungal-host root interactions (5, 6, 10, 11), the results shown here deal with particulate fractions isolated from host roots. Root caps were rapidly isolated from Ri T-DNA transformed carrot roots (D. carota L.) grown in liquid culture either in the presence or absence of phosphorus. For the bioassay, isolated root caps and separated root mucilage were resuspended in a small volume of sterile water and applied to a Petri plate containing germinated G. gigantea spores. Both particulate fractions readily stimulated hyphal branching of the AM fungus. The branching stimulator associated with root caps was either tightly bound and released slowly or alternatively, border cells from the root caps were still viable and possibly secreting branching stimulators during the bioassay. |
