Tall fescue aluminum tolerance is affected by neotyphodium coenophialum endophyte
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Roots of endophyte-infected (E+) tall fescue (Festuca arundinacea Schreb.) exude more phenolic-like reductants than roots of endophyte-free (E-) plants when mineral stressed. Phenolic compounds are efficient chelators of aluminum (Al) and may influence Al tolerance in many plant species. The objective of our study was to determine if enhanced release of phenolic compounds by roots of E+ plants contributes to Al tolerance in tall fescue. Two cloned genotypes (DN2 and DN11) of tall fescue infected with their naturally occurring fungal endophyte Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon and Hanlin and their noninfected isolines were grown in nutrient solutions at 0 M Al (Al-) and at 640 M Al (Al+) under controlled environment conditions. Root and shoot dry matter (DM) of endophyte-infected tall rescue was greater in E+ than E- plants by 57% and 40%, respectively, when plants were grown without Al. Endophyte infection did not affect root and shoot DM of tall fescue grown with Al but relative (to Al-treatment) reduction in root and shoot DM was greater in E+ than E- plants. In response to Al stress, more Al (47%) and P (49%) could be desorbed from root surfaces of E+ than E- plants. Aluminum concentrations in roots of E+ plants were 35% greater and P concentrations were 10% less than those determined in roots of E-plants. No differences in mineral concentrations were observed in shoots, regardless of endophyte status, or Al level in nutrient solution. Roots of E+ plants increased pH of both Al- and Al+ nutrient solutions to a greater extent than roots of E- plants in a 48 h interval. Our results show that more Al can be sequestered on root surfaces and in root tissues of endophyte-infected tall fescue than in plants devoid of endophyte. Aluminum sequestration was greater on root surfaces and in root tissues of E+ than E- plants of a given tall fescue genotype. Our results suggest that increased exudation of phenolic-like compounds from roots of endophyte-infected tall fescue may be directly involved in Al tolerance and serves as a mechanism for widespread adaptability and success of endophyte-tall fescue associations.
