Ultraviolet-induced autofluorescence of arbuscular mycorrhizal root infections: an alternative to clearing and staining methods for assessing infections

Abstract

Arbuscules in vesicular–arbuscular mycorrhizal (VAM) infections in untreated roots autofluoresced when viewed with an epifluorescence microscope. Ultraviolet-induced fluorescence was observed with the same filtering system used to detect fluorescein staining. Plant roots were examined from five plant families, grown under a variety of conditions, and infected with several species of VAM fungi. In every case, autofluorescent arbuscules were observed. Vesicles, spores, and hyphae did not autofluoresce under these same conditions. Fluorescence was not observed in ectomycorrhizae or pathogenic fungal infections. Cut mycorrhizal root segments from greenhouse- and field-grown plants were evaluated for infection using ultraviolet light and clearing and staining. No significant differences were found in the percent VAM infection as determined by the two methods on the same root segments. Applications and considerations in the use of the ultraviolet method for measuring infections as well as some preliminary observations on using fluorescein diacetate are discussed.