Hartig net

The hyphae in the Hartig net acquire sugars from the plant root, which are transported to the external mycelium to provide a carbon source to sustain fungal growth.

[2][4] The hyphae in the Hartig net formed by some ECM fungi are described as having transfer-cell like structures, with highly folded membranes that increase surface area and facilitate secretion and uptake of resources exchanged in the mutualistic symbiosis.

[6][7] The initial development of the Hartig net likely involves a regulated decrease of plant defense responses, thus allowing fungal infection.

[8] Unlike some plant root pathogenic fungi, ectomycorrhizal fungi are largely unable to produce many plant cell-wall-degrading enzymes, but increased pectin modification enzymes released by Laccaria bicolor during fungal infection and Hartig net development indicate that pectin degradation may function to loosen the adhesion between neighboring plant cells and allow room for hyphal growth between cells[9][10] This Hartig net structure is common among ectomycorrhizal fungi, although the depth and thickness of the hyphal network can vary considerably depending on the host species.

[20][21] In the Hartig net of Amanita muscaria within poplar roots, expression of important fungal enzymes for trehalose biosynthesis was higher than in the extrametrical mycelium, indicating that trehalose production may function as a carbohydrate sink, increasing fungal demand of plant photosynthesized carbon compounds through the symbiotic exchange.