Evidence for copper binding by extracellular root exudates of tall fescue but not perennial ryegrass infected with Neotyphodium spp. endophytes
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abstract
Infection of tall fescue (Festuca arundinacea Schreb.) with its endemic Neotyphodium 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 Cu 2+-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 Cu 2+-binding activity and endophyte effects on heavy metal concentrations in shoots and roots were specific for each variety. The Cu 2+-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. 2004 Kluwer Academic Publishers.
