Histochemical Staining of Arbuscular Mycorrhizal Roots for Quantification of Fungal Colonization, High-Resolution Imaging, and Localization of Symbiotic Gene Expression.

Histochemical staining and microscopy-based techniques have been widely used to detect, quantify, and analyze the morphology of arbuscular mycorrhizal fungi (AMF) in roots. Here, we describe a traditional standardized method for staining of AMF in colonized roots using trypan blue, along with possible modifications to adapt the protocol to specific needs, such as root type or reducing the use of toxic reagents. We also summarize common approaches for quantifying arbuscular mycorrhizal colonization. In addition, we present a simple fluorescent staining protocol, using wheat germ agglutinin-Alexa Fluor conjugates, for high-resolution imaging of fungal colonization patterns and arbuscule morphology in roots. Finally, we describe a GUS staining method for localizing the promoter activity of plant genes potentially involved in mycorrhization, using transformed mycorrhizal hairy roots carrying promoter-GUS fusions.