HYPHAE: CHARACTERISTICS, FUNCTIONS AND TYPES - BIOLOGY - 2024

The hyphae are filamentous structures constituting the cylindrical body of multicellular fungi. They are formed by a row of elongated cells surrounded by a chitinous cell wall. The cells that compose it may or may not be separated from each other by a transverse cell wall (septum).

The mycelia of filamentous fungi consist of interconnected hyphae that grow at their vertices and branch subapically. Apical growth can reach speeds greater than 1 µm / s.

Hypha and mycelium. Taken and edited from es.winner.wikia.com

Hyphae have multiple functions associated with growth, nutrition, and reproduction. According to some authors, the success of fungi to colonize terrestrial ecosystems is due to their ability to form hyphae and mycelia.

characteristics

The hyphae generally have a tubular or fusiform shape, they can be simple or branched. They can be septate or not, if they are septate, the septum has a central pore of 50-500 nm that allows inter-compartment and interhiphal cytoplasmic mixing.

They may or may not develop clamp connections, or fibulae, between adjacent cells of the same hypha. The cell walls are chitinous in nature, of different thickness, which can be embedded in a matrix of mucilage or gelatinized materials.

Hyphae can be multinucleated (coenocytic) or formed by uni, bi, poly or anucleated cells. Hyphae with binucleated cells can occur by fusion of hyphae of uninucleated cells (dikaryotes) or by migration of nuclei between neighboring cells through the central pore. Due to the latter cause, cells can also be polynucleated or lack nuclei.

The growth of the hyphae is apical. The distal area of ​​the hypha, called the apical body (Spitzenkörper), has a spherical shape, it is not separated from the rest of the hypha by a membrane, however, it functions as an organelle.

The apical body is made up of vesicles, microtubules, microfilaments, and microvesicles. The latter come mainly from the Golgi apparatus. This set of structures forms a very dense and dark area. The apical body is involved in the synthesis of the cell wall.

Features

The modular pattern of organization of hyphae contributes to their differentiation. In these, the apical cells generally participate in the acquisition of nutrients and have a sensory capacity to detect the local environment.

The sub-apical cells are in charge of generating new hyphae through lateral branches. The resulting network of hyphae is called the mycelium.

The branching of the hyphae appears to have two general functions. On the one hand, it serves to increase the surface of the colony, which helps the fungus to increase the assimilation of nutrients.

On the other hand, the lateral branches participate in hyphal fusion events, which seems to be important in the exchange of nutrients and signals between different hyphae in the same colony.

Generally speaking, hyphae are associated with multiple different functions, depending on the specific requirements of each species of fungus. These include:

Nutrient absorption

Parasitic fungi have specialized structures at the ends of their hyphae, called haustoria. These structures penetrate the host tissue, but not its cell membrane.

The haustoria work by releasing enzymes that break down the cell wall and allow the movement of organic matter from the host to the fungus.

Arbuscular mycorrhizal fungi, on the other hand, form structures called arbuscules and vesicles at the ends of the hypha within the cortical cells of host plants.

These structures, which are used by fungi for the uptake of nutrients, act as a complement to the plant root in the uptake of nutrients, especially phosphorus. They also increase the host's tolerance to abiotic stress conditions, and the fixation of molecular nitrogen.

Saprophytic fungi present structures called rhizoids for the absorption of nutrients, which are equivalent to the roots of higher plants.

Nutrient transport

Several species of fungi exhibit hyphae composed of structures called mycelial strings. These strings of mycelium are used by fungi to transport nutrients long distances.

Nematode capture

At least 150 species of fungi have been described as predators of nematodes. To capture their prey, these fungi developed different types of structures in their hyphae.

These structures act as passive (adhesive) or active traps. Passive traps include buttons, branches, and sticky nets. Among the active traps are constrictor rings.

Electron micrograph of a nematode trapped by fungal or constrictor rings. By Apsnet.org. Taken and edited from

Reproduction

Generative hyphae can develop reproductive structures. Additionally, some haploid hyphae can fuse in pairs to form binucleate haploid hyphae, called dikaryotes, later these nuclei will perform karyogamy to become diploid nuclei.

Types

According to its cell division

Septate: cells are separated from each other by incomplete partitions called septa (with septa)

Aseptate or coenocytic: multinucleated structures without septa or transverse cell walls.

Pseudohyphae: it is an intermediate state between a unicellular phase and another mycelial. This is a state of the yeast and is formed from budding. The buds do not detach from the stem cell, and later elongate until giving rise to a structure similar to the true hypha. Its appearance occurs mainly when there is environmental stress due to lack of nutrients or any other cause.

According to its cell wall and its general shape

The hyphae that form the fruiting bodies can be identified as generative, skeletal, or junctional hyphae.

Generative: relatively undifferentiated. They can develop reproductive structures. Its cell wall is thin, or slightly thickened. They are generally septate. They may have, or lack, fibulae. They can be embedded in mucilage or gelatinized materials.

Skeletal: they are of two basic shapes, elongated or typical and fusiform. The classic skeletal hypha is thick-walled, elongated, unbranched. It has few septa and lacks fibulae. The spindle-shaped skeletal hyphae are centrally swollen and are often extremely wide.

Enveloping or union: they do not have septa, they are thick-walled, highly branched and with sharp ends.

Hyphal systems

The three types of hyphae that form fruiting bodies give rise to three types of systems that can be present in a species:

Monomitic systems: they present only generative hyphae.

Dimitic: they present generative hyphae and skeletal or enveloping hyphae, but not both.

Trimitic: they present the three types of hyphae at the same time (generative, skeletal and enveloping).

References

1. M. Tegelaar, HAB Wösten (2017). Functional distinction of hyphal compartments. Scientific Reports.
2. KE Fisher, RW Roberson (2016). Fungal hyphal growth - Spitzenkörper versus Apical Vesicle crescent. Fungal Genomics & Biology.
3. NL Glass, C. Rasmussen, MG Roca, ND Read (2004). Hyphal homing, fusion and mycelial interconnectedness. Trends in Microbiology.
4. N. Roth-Bejerano, Y.-F. Li, V. Kagan-Zur (2004). Homokaryotic and heterokaryotic hyphae in Terfezia. Antonie van Leeuwenhoek.
5. SD Harris (2008). Branching of fungal hyphae: regulation, mechanisms and comparison with other branching systems Mycologia.
6. Hypha. On Wikipedia. Recovered from en.wikipedia.org/wiki/Hypha