Hypha

Hypha is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.

Structure and Growth

A hypha consists of one or more cells surrounded by a tubular cell wall. In most fungi, hyphae are divided into cells by internal cross-walls called "septa". Septa are usually perforated by pores large enough for ribosomes, mitochondria and sometimes nuclei to flow among cells. The major structural polymer in fungal cell walls is typically chitin, in contrast to plants and oomycetes that have cellulosic cell walls, and bacteria, which have cell walls of peptidoglycan.

Hyphae grow at their tips. During tip growth, cell walls are extended by the external addition of new layers of wall polymers. The spitzenkörper is an intracellular organelle associated with tip growth. It is composed of an aggregation of membrane-bound vesicles containing cell wall components. The spitzenkörper moves to the hypha tip to supply new cell wall material.

Types of Hyphae

There are three main types of hyphae: generative hyphae, skeletal hyphae, and binding hyphae.

• Generative hyphae are relatively undifferentiated and can develop reproductive structures.
• Skeletal hyphae are of two basic types, both of which are typically hyaline and acellular: classical skeletal hyphae, which have a rigid, thick wall, and are not readily fragmented; and pseudoskeletal hyphae, which are more fragile and can become fragmented, giving rise to more hyphae.
• Binding hyphae are thick-walled and frequent branching, often resembling a tree in shape. They are typically found in the mature parts of the mycelium.

Role in Disease

In pathogenic fungi, hyphae are structures that allow the fungus to invade tissues. Some fungi can switch between yeast phase and hyphal phase in response to environmental conditions; this is known as dimorphism. Hyphal growth enables the fungus to penetrate the substratum, avoid competition, and spread over surfaces.

See Also

• Mycelium
• Fungus
• Septa
• Spitzenkörper

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