Аннотация:Under certain conditions, fungi are capable to fast (down to seconds) change the size of their cells. For example, it is known that the cells of many species of yeasts under hyperosmosis instantly and reversibly shrink entirely, without plasmolysis, with a decrease in volume of up to 40% or more. There is limited data that filamentous fungi can also instantly change the diameter of their unspecialized hyphae. This property is fundamental and is a powerful tool for survival and preservation of the physiological functions of the fungus in sharply changing external conditions, but requires detailed study. In this work, which is a large-scale (more than 50,000 cells measured) light microscopic study, the ability of three unrelated basidiomycete species to fast change the diameter of their hyphae under the influence of various factors was analyzed. It was found, for example, that all three fungi respond similarly to moderate hyperosmotic shock and shrink by an average of 12-14% in diameter, but inhibitors of actin assembly can cause both expansion and shrinkage of hyphae, or have no effect on a fungus. Combining the current results with those previously obtained in the study of macroinvagination systems of the fungal plasma membrane, different approaches for basidiomycetes to respond to sudden stress changes were proposed. The previously presented curtain model has also been advanced. The model describes a general mechanism for the rapid regulation of hyphal sizes, which involves the elastic properties of the cell wall, adhesion of the plasma membrane to it, regulation of turgor, a system of actin cables that regulate the tension of the plasma membrane and cell size, as well as a complex system of macroinvaginations of the plasma membrane, ensuring constant integrity and functionality of the latter.