Evidence for copper binding by extracellular root exudates of tall fescue but not perennial ryegrass infected with Neotyphodium spp. endophytes

Infection of tall fescue (Festuca arundinacea Schreb.) with its endemicNeotyphodium coenophialum-endophyte (Morgan-Jones and Gams) Glenn, Bacon and Hanlin appears to reduce copper (Cu) concentrations in forage and serum of grazing animals, contributing to a range of immune-related disorders. A greenhouse experiment was conducted to identify effects of novel endophyte strains on Cu acquisition by tall fescue (Festuca arundinacea Schreb.) varieties Grasslands Flecha and Jesup infected with a novel, non ergot producing endophyte strain AR542, and two perennial ryegrass (Lolium perenne L.) varieties Aries and Quartet infected with a novel, non lolitrem B producing strain AR1, and their noninfected (E-) forms. Individual endophyte/grass associations were cultivated in nutrient solutions at 1.0 (P+) and 0.0 mM (P-) phosphorus concentrations. The Cu2+-binding activity of extracellular root exudates, and concentrations of Cu and other heavy metals in roots and shoots were measured. Extracellular root exudates of AR542-infected vs. E- tall fescue had higher Cu2+-binding activity only in P- nutrient solution as shown by lower concentration of free Cu2+ (0.096 vs. 0.188 mmol Cu2+ g-1 root DM, respectively). The Cu2+-binding activity by root exudates of perennial ryegrass was not affected by endophyte infection, but was higher (i.e., lower concentration of free Cu2+) in P- vs. P+ nutrient solution (0.068 vs. 0.114 mmol Cu2+ g-1 root DM). In this hydroponic experiment, Cu concentrations in shoots of both grasses were not a function of Cu2+-binding activity and endophyte effects on heavy metal concentrations in shoots and roots were specific for each variety. The Cu2+-binding activity of extracellular root exudates may affect Cu accumulation by field-grown, endophyte-infected tall fescue under P-limiting growth conditions and warrants verification by more specific methods.