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Mechanisms of aluminum tolerance in mycorrhizal broomsedge plants.
Ning, Jianchang1, Cumming, Jonathan1, 1
ABSTRACT- Broomsedge (Andropogon virginicus) is a dominant species colonizing stressful soil habitats in the eastern United States. In areas subjected to strip-mining, the remaining overburden may present challenges to plants, such as low pH and elevated aluminum (Al). Previously, we found that the association of arbuscular mycorrhizal (AM) fungi with broomsedge roots significantly increased Al resistance of the host plant. To investigate the mechanisms of this benefit, we assessed organic acid production by roots of broomsedge plants colonized by two isolates of the AM fungus Glomus clarum. Rhizosphere organic acids chelate and detoxify Al in a variety of plant species. Broomsedge plants were grown in sand culture for eight weeks and exposed to Al ranging from 0 to 1000 M. Both isolates increased host plant Al resistance as measured by growth and Al-induced perturbations to host plant nutrient accumulation. In comparison to non-mycorrhizal controls, mycorrhizal isolates reduced the accumulation of Al in broomsedge shoots and roots, although to different degrees. In non-mycorrhizal plants, exposure to Al induced a shift in organic acid profiles from mono- to di- and tricarboxylic acids. This pattern was not observed for mycorrhizal plants, suggesting that some yet-to-be determined Al resistance system is functioning in the AM fungal-broomsedge symbiosis.
KEY WORDS: metal tolerance, mycorrhizal fungi, Glomus clarum