Fungal calcium oxalate in mycorrhizae of Monotropa uniflora

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Abstract
Monotropa uniflora is an achlorophyllous angiosperm that is obligately mycotrophic. The "monotropoid" mycorrhizae it forms resemble ectomycorrhizae but are distinguished by elaborations of the epidermal cell walls that surround intruding fungal hyphae. Monotropoid mycorrhizae collected from blooming plants in late summer contained calcium oxalate crystals between mantle hyphae. The crystals appeared to form in association with hyphal walls and grew into a matrix outside the hyphae. Production of calcium oxalate by M. uniflora's mycobiont seems to be a coordinated metabolic process rather than a random precipitation event. The significance of calcium translocation and isolation as calcium oxalate to this mycorrhizal fungus is unclear, but the presence of extensive crystal deposits during and after flowering of the host plant suggests a possible link with the nutrient transfer occurring at that time. Mycorrhizal regulation of calcium may affect the availability of mineral nutrients to the associated Monotropa plants. Key words: Monotropa uniflora, mycorrhiza, calcium oxalate, ectomycorrhiza.