Comparative ultrastructural analysis of mycorrhizal associations

Abstract

Electron microscopy is a powerful tool in understanding functional mechanisms in symbiosis (i.e., recognition and transfer of nutrients between partners), but mycorrhizal associations are not yet so well known as host–pathogen and host – mutualistic bacterial associations. However, the study of mycorrhizal ultrastructure has provided some interesting information. In fact unknown symbionts can be recognized with electron microscopy and mycorrhizae can be classified according to a sequence linking intercellular and intracellular interactions between host and fungus. General conclusions can be drawn from this ultrastructural sequence. (i) The most significant cytological feature in mycorrhizae is the presence of an interface through which partners communicate along a vast surface area. This is the key area for symbiotic interactions (both recognition and nutrient transfer) and can vary a great deal mostly in intracellular interactions. (ii) The ultracytochemical aspects of those interfaces, mostly as regards the components of the interfacial matrix, appear quite different from those of host–pathogen associations and suggest a compatibility mechanism. (iii) As regards the transfer of nutrients, even though it has been claimed that transfer of nutrient in all intracellular interactions is achieved by a digestion mechanism of the fungus by the host, available ultrastructural data are not consistent with this hypothesis.

A light‐ and electron‐microscopic study on a vesicular–arbuscular host‐fungus interaction in gametophytes and young sporophytes of the Gleicheniaceae (Filicales).

“…In host cells with cytoplasmic arbuscules, cytoplasm and cell organelles increase and starch disappears from plastids. This corresponds to the reports on the development of arbuscular host-fungus interactions within roots (Scannerini & Bonfante-Fasolo, 1983) and suggests an active symbiosis with nutrient transfer. Campbell {1908) studied the endophytic fungi in gametophytes of three species of the Gleicheniaceae.…”

Variations in chromatin structure in host nuclei of a vesicular arbuscular mycorrhiza

“…The functional morphology of cell to cell interactions in vesicular-arbuscular (VA) mycorrhizas is well defined in regard to host/fungus interfaces and cytoplasmic organelles (for reviews see Scannerini & Bonfante-Fasolo, 1983;Bonfante-Fasolo & Gianinazzi-Pearson, 1986;Bonfante-Fasolo, 1987, 1988GianinazziPearson & Gianinazzi, 1988). However, the patterns of the host cell nuclei remain unclear.…”

Live-Cell Imaging Reveals Periarbuscular Membrane Domains and Organelle Location in Medicago truncatula Roots during Arbuscular Mycorrhizal Symbiosis

“…As the penetrating hypha enters the cortical cell, the plant plasma membrane is not breached but invaginates and is then extended to form the periarbuscular membrane (Cox and Sanders, 1974;Bonfante-Fasolo, 1984;Toth and Miller, 1984). Transmission electron microscopy (TEM) studies showed accumulation of cytoplasm and organelles, including endoplasmic reticulum (ER), Golgi bodies, plastids, and mitochondria, in the area around arbuscule branches (Cox and Sanders, 1974;Scannerini and Bonfante-Fasolo, 1982). In addition, the tonoplast invaginates, and the TEM micrographs revealed the presence of multiple small vacuole compartments (Cox and Sanders, 1974;Toth and Miller, 1984), which led to the interpretation that arbuscule development is accompanied by fragmentation of the plant central vacuole (Scannerini and Bonfante-Fasolo, 1982;Bonfante and Perotto, 1995;Gianinazzi-Pearson, 1996;Harrison, 1999).…”

“…Transmission electron microscopy (TEM) studies showed accumulation of cytoplasm and organelles, including endoplasmic reticulum (ER), Golgi bodies, plastids, and mitochondria, in the area around arbuscule branches (Cox and Sanders, 1974;Scannerini and Bonfante-Fasolo, 1982). In addition, the tonoplast invaginates, and the TEM micrographs revealed the presence of multiple small vacuole compartments (Cox and Sanders, 1974;Toth and Miller, 1984), which led to the interpretation that arbuscule development is accompanied by fragmentation of the plant central vacuole (Scannerini and Bonfante-Fasolo, 1982;Bonfante and Perotto, 1995;Gianinazzi-Pearson, 1996;Harrison, 1999). Immunolocalization studies showed that arbuscule development is accompanied by reorganization of plant cytoskeletal components that surround the developing arbuscule and likely directs membrane deposition and organelle accumulation Bonfante, 1997, 1998;Blancaflor et al, 2001).…”