SPORANGIOPHORE: CHARACTERISTICS AND FUNCTIONS - BIOLOGY - 2024

A sporangiophore is a specialized aerial hypha that serves as a support or peduncle for one or more sporangia in some fungi. The word comes from three Greek words: spora, which means seed; angei, angeo, which means conduit, conducting vessel or blood vessel; and phor, phoro, which means "that carries."

Fungi are eukaryotic organisms, that is, they have in their cytoplasm a defined nucleus with a nuclear membrane and organelles with membranes. The cells of fungi are similar in structure to those of other organisms. They have a small nucleus with the genetic material surrounded and protected by a double membrane, in addition to several organelles with their membrane, dispersed in the cytoplasm.

Figure 1. Sporangiophores in the fungus Rhizopus stolonifer, bread mold. Source: WDKeeper

Historically fungi were included in the plant kingdom, but were later separated from plants in a separate kingdom due to their special distinctive characteristics. Among these characteristics, it can be mentioned that fungi do not have chlorophyll, so they cannot photosynthesize (unlike plants).

Fungi are also distinguished by having unique structural characteristics, such as particular chemical components in their cell walls and membranes (chitin, for example).

Chitin is a polymer that provides toughness and rigidity to the structures where it is present. It has not been reported in plants, only in fungi and in the exoskeleton of some animals such as shrimp and beetles.

Fungi are also distinguished as living organisms by unique physiological factors, such as their extracellular digestion by absorption and their reproduction with an asexual and sexual cycle. For all these reasons, mushrooms are classified in a special kingdom called Fungi (mushrooms).

Characteristics of sporangiophores

The sporangiophores, like hyphae, are tubular structures that contain cytoplasm and nucleus, have walls made up of chitin and glucan.

As specialized hyphae, they are aerial hyphae that form sac-like structures at their ends, called sporangia.

Features

The sporangiophores as specialized aerial hyphae, fulfill important functions of formation, support and peduncle of the sporangia or sacs that contain the spores in primitive fungi.

Hyphae and mycelium

Fungi have a general morphology made up of hyphae that together form a mycelium.

A typical fungus has a mass of tube-shaped filaments that have a rigid cell wall. These tubular filaments are called hyphae, which develop by growing in a branching fashion. Branching occurs repeatedly forming a complex network that expands radially, called mycelium.

The mycelium, in turn, forms the thallus or body of the fungi. The mycelium grows taking nutrients from the environment and when it has reached a certain stage of maturity, it forms reproductive cells called spores.

The spores are formed through the mycelium in two ways: one, directly from the hyphae, and another, in the so-called special fruiting bodies or sporangiophores.

The spores are released and dispersed in a wide variety of mechanisms and when they reach a suitable substrate, they germinate and develop new hyphae, which repeatedly grow, branch, and form the mycelium of a new fungus.

The growth of the fungus occurs at the ends of the tubular filaments or hyphae; thus, fungal structures are made up of hyphae or portions of hyphae.

Some fungi, like yeast, do not form a mycelium; They grow as individual cells, they are single-celled organisms. They multiply or reproduce forming suckers and chains or in certain species they reproduce by cellular fission.

Structure of hyphae

Aquatic fungus of the Chytridiomicota group, Allomyces sp. Its filaments or hyphae are observed. Source: TelosCricket

In the vast majority of fungi, the hyphae that form the thallus or fungal body have cell walls. It has already been said that a hypha is a highly branched tubular structure, which is filled with cytoplasm.

The hypha or tubular filament may be continuous or divided into compartments. When there are compartments, these are separated by partitions called septa, which are made up of interlocking walls.

Non-septate hyphae

In less evolved (more primitive) fungi, the hyphae are generally non-septate, without compartments. In these undivided hyphae, which do not have septa and form a continuous tube (called coenocytes), the nuclei are dispersed throughout the cytoplasm.

In this case, the nuclei and mitochondria can be easily transported or translocated along the hyphae, and each hypha can contain one or more nuclei depending on the type of fungus or the stage of development of the hypha.

Septate hyphae

In more evolved fungi, the hyphae are septate. The septa have a perforation or pore. This pore allows the movement of the cytoplasm from one cell to another; This movement is called cytoplasmic migration.

In these fungi with perforated septa, there is a rapid movement of various types of molecules within the hyphae, but nuclei and organelles such as mitochondria, which are larger, do not pass through the pore.

Structure of the septa

The structure of the partitions or septa is variable depending on the type of fungus. Some fungi have septa with a sieve or network structure, called pseudosept or false septa. Other fungi have partitions with one pore or few pores.

Basidiomycota fungi have a septum structure with a complex pore, called the dolipore septum. The dolipore is made up of a pore, surrounded by a ring and a covering that covers them both.

Chemical composition of hyphal walls

Hyphal walls have complex chemical composition and structure. This composition varies depending on the type of fungus. The main chemical components of the hyphal walls are two polymers or macromolecules: chitin and glucan.

There are many other chemical components of the hyphal walls. Some components give the wall greater or lesser thickness, others more rigidity and resistance.

Additionally, the chemical composition of the hyphal wall varies according to the stage of development of the fungus.

Types of hyphae

As the mycelium of the so-called superior or evolved fungi grows, it is organized into compact masses of hyphae of different sizes and functions.

Sclerotia

Some of these masses of hyphae, called sclerotia, become extremely hard and serve to support the fungus in periods of adverse temperature and humidity conditions.

Assimilating somatic hyphae

Another type of hyphae, somatic assimilating hyphae, excrete enzymes that externally digest nutrients and then absorb them. For example, the hyphae of the fungus Armillaria mellea, black and similar to a shoelace, are differentiated and fulfill functions of conducting water and nutrient materials from one part of the body of the fungus (or thallus) to another.

Sporangiophores

When the mycelium of the fungus reaches a certain stage of growth and maturity, it begins to produce spores, either directly on the somatic hypha or more frequently in specialized hyphae that produce spores, called sporiferous hyphae.

The sporiferous hyphae can be arranged singly or in intricately structured groups called fruiting bodies, sporophores, or sporangiophores.

The sporophores or sporangiophores are hyphae with sack-like ends (sporangia). The cytoplasm of these hyphae called sporangiophores is shed into spores, called sporangiospores.

Sporangiospores may be naked and possess a flagellum (in which case they are called zoospores) or they may be walled, non-moving spores (called aplanospores). Zoospores can swim by propelling themselves with their flagellum.

References

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