Ecological role and modification of the plant and fungal cell structure in the interface between host root and ectomycorrhizal hyphae

Abstract

In this review, we described how the plant and fungal cell structures are modified to interface between the host root and ectomycorrhizal (ECM) hyphae and what these processes imply in the forest ecosystem. Cytoplasmic polyphenols induce the colonization of ECM hyphae. The root hairs bend and collapse in contact with hyphae, which adhere closely to mucilage and are embedded in the epidermis. Accordingly, root hairs respond by developing thickened cell walls as the interaction progresses. After first contact with hyphae, their morphology changes with considerable branching and an increase in hyphal diameter. Hyphal morphology of the inner mantle is modified as tissue-like, with compact, flat and repeatedly branched hyphae. Inner mantle hyphae of ECM penetrate the inter-epidermal cells. The Hartig net is linked with inter-epidermal cells (angiosperms) or inter-epidermal and inter-cortical cells (conifers) by the highly branched labyrinthine hyphae. The epidermal cells of angiosperms are radially elongated. Polyphosphate granules are precipitated as an artefact of chemical specimen preparation in the vacuoles of the ECM mantle and Hartig net hyphae. Higher proportions of absorbed phosphate are translocated into the polyphosphate pool in the ECM roots. The wall ingrowth phenomenon, which is a response of root cells to mycorrhizal fungi for development as transfer cells, occurs on the epidermal cells adjacent to the mantle hyphae and the Hartig net hyphae interfacing with the epidermal cell wall, exchanging nutrients between plant and fungus in ECM. Eventually, the plant and fungal cell structures are modified to interface mutually and the outstanding ecological role of symbiont ECM hyphae is to increase the exploitation of phosphorus (P) to host tree from soil.