Amyloid (mycology)

In mycology, the term "amyloid" describes a microscopic staining reaction observed in certain fungal structures, particularly spores, asci, and hyphae, when treated with Melzer's reagent. Melzer's reagent is a solution composed of iodine, potassium iodide, chloral hydrate, and water. An amyloid reaction indicates that the fungal structure contains polysaccharides (complex carbohydrates), specifically certain types of glucans, that bind with iodine in the reagent, resulting in a blue-black or gray-blue color change under a microscope.

The presence or absence of an amyloid reaction, as well as the intensity of the staining, is a useful characteristic in fungal identification and classification. It is a key morphological feature used in taxonomic keys to differentiate between various genera and species.

A positive (amyloid) reaction indicates that the structure stains blue-black or gray-blue with Melzer's reagent. A negative (inamyloid) reaction indicates that the structure does not change color, remaining hyaline (clear) or yellowish. A dextrinoid reaction is a related but distinct staining reaction, where the structure turns reddish-brown or brown in Melzer's reagent.

It is important to note that the exact mechanism of the amyloid reaction is not fully understood, but it is believed to involve the complexation of iodine molecules within the polysaccharide structure.