Large-scale tubular and tubular-lamellar intracellular membrane systems of fungi.

Filamentous fungi and oomycetes have four large intracellular membrane systems consisting of tubes, lamellae, or a combination thereof. Such elongated membrane structures can extend for tens of micrometers in hyphal cells, branching and connecting into bundles and networks. These systems are represented by tubular vacuoles, elongated mitochondria, endoplasmic reticulum, and macroinvaginations of the plasma membrane. They are most developed in xylotrophic and mycorrhiza-forming basidiomycetes. This review examines three membrane systems, excluding the macroinvaginations. Various morphotypes of these membrane systems, characteristic of certain taxonomic and ecological-trophic groups of fungi and oomycetes, are considered. Hypotheses explaining the role of large-scale membrane systems in the life processes of filamentous organisms are presented. These hypotheses are still relatively speculative because they rely more on morphology and topology than on the poorly studied physiology of these systems. The synthesizing hypothesis posits that, at least in the apical region of hyphae, tubular vacuoles, elongated mitochondria, and the endoplasmic reticulum interact closely and may facilitate intrahyphal solute transport, independent of mass flow and turgor gradients. Further studies of large-scale membrane systems are important for developing the structural physiology of filamentous fungi and other organisms.