Intraradical protein and glomalin as a tool for quantifying arbuscular mycorrhizal root colonization

Abstract

Assessment of root colonization by arbuscular mycorrhizal fungi (AMF) is largely dependent upon traditional microscopic techniques as no consistent biochemical marker for AMF is available outside of DNA based methods. Glomalin is an AMF produced protein that has potential to serve as a specific biomarker for rapid detection of AMF. We tested whether AMF-colonized roots contained greater concentrations of two glomalin-related protein fractions, Bradford-root protein (BRP) and MAb32B11-immunoreactive-root protein (IRP), compared to non-colonized controls. Additionally, we tested if these protein fractions were correlated with AMF colonization rate. AMF colonization significantly increased IRP within roots of Bromus inermis colonized by several different AMF isolates. BRP and IRP were also increased in Daucus carota (grown under sterile in vitro conditions), and Plantago lanceolata and Sorghum bicolor (grown in the greenhouse). The relationships between intraradical concentrations of both BRP and IRP and AMF root colonization were approximated by both linear and non-linear models in all plants (r2 from 0.50 to 0.94). Clearly, this method could be useful at least in assessing presence/absence of AMF colonization, for example in large-scale screening situations (e.g., testing for mycorrhizal mutants, verifying colonization in the horticultural/restoration industry). While the MAb32B11-ELISA assay was also useful in detecting AMF colonization, it did not consistently offer greater resolution/precision. This analysis method is more involved and hence not as practical, and we also could not conclusively attribute the antibody reaction to cross-reactivity or a true glomalin signal in roots.