Evidence for chemical changes on the root surface of tall fescue in response to infection with the fungal endophyte Neotyphodium coenophialum

Endophyte-infected (E+) tall fescue (Festuca arundinacea Schreb.) plants grown in phosphorus (P) deficient soils accumulate more P in roots and shoots than noninfected isolines, In a growth chamber experiment, four tall fescue genotypes DN2, DN4, DN7, and DN11, infected with their naturally occurring strains of Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon & Hanlin, and their noninfected isolines (E-), were cultivated in nutrient solution at two P levels: 31 ppm (P+) and 0 ppm (P-) for 4 wk. The Fe(3+) reducing activity of extracellular reductants and intact root tissues, and total phenolic concentration in roots and shoots were measured. Endophyte infection significantly increased Fe(3+) reducing activity rate of extracellular reductants (9.6 x 10(-3) mu mol Fe(3+) h(-1) g(-1) root FW) when compared to E- plants (3.9 x 10(-3)) and Fe(3+) reduction rate of intact root tissues (6.16 and 4.48 mu mol Fe(3+) h(-1) g(-1) root FW, respectively for E+ and E- plants). In response to P deficiency, Fe(3+) reduction rate of intact root tissues increased in E+ plants by 375% when compared to E- plants, whereas no significant differences were observed when P was provided. Total phenolic concentration was 20% greater in shoots of E+ plants than in E- plants. In response to P deficiency, total phenolic concentration significantly increased in roots of E+ plants by 7%, and decreased in roots of E- plants by 10%, The west active Fe(3+) reducing zones were located along branching of secondary and tertiary roots. The Fe(3+) reducing activity on the root surface and total phenolic concentration in roots and shoots increased dramatically in response to endophyte infection, especially under P limiting conditions.