Explain the structure of sporangiophore and dehiscence of sporangium of Rhizopus?

 Explain the structure sporangiophore and dehiscence of sporangium of Rhizopus? 

Rhizopus is a widely distributed genus of about ten filamentous fungal species in the family Rhizopodaceae (formerly Mucoraceae) of the order Mucorales. Numerous species are important for industry, and some cause diseases in both plants and animals. One such species is Rhizopus stolonifer, sometimes known as the common bread mold.Rhizopus is a widely distributed genus of about ten filamentous fungal species in the family Rhizopodaceae (formerly Mucoraceae) of the order Mucorales. Numerous species are important for industry, and some cause diseases in both plants and animals. One such species is Rhizopus stolonifer, sometimes known as the common bread mold.

When two compatible and physiologically different mycelia are present, rhizopus can reproduce sexually. The quickly proliferating colonies have a texture akin to cotton candy, sometimes known as candy floss or fairy floss, and change from white to dark as they release spores.

Numerous Rhizopus species are frequently employed in industrial operations. R. arrhizus (R. oryzae) is beneficial for the biosorption (passive adsorption of chemical pollutants by an organism) of heavy metals, the synthesis of lactic acid and cortisone, and the fermentation of alcohol. Fumaric acid and biotin are produced by R. delemar, while lactic acid, cortisone, and fumaric acid are produced by R. stolonifer. Several species are significant in several traditional alcoholic beverages and some meals, such tempeh, in Asia.

Rhizopus Life Cycle
Rhizopus reproduces through vegetative, asexual, and sexual means.

In vegetative reproduction, stolons are fragmented, and each piece develops into a whole mycelium on its own.

The process of sporangiospore and chlamydospore development is known as asexual reproduction.

1. Sporangiospore Formation: In sporangia of aerial mycelium known as sporangiophores, sporangiospores are generated terminally. They form in an environment that is favorable.

The genus Rhizopus is distinguished by pigmented rhizoids and stolons, as well as by the apophysate, columellate, multispored, and typically globose sporangia that emerge from nodes right above the rhizoids. The apophyses and columella frequently collapse to produce an umbrella-like structure following spore discharge. In many species, sporangiospores are globose to ovoid, single-celled, hyaline to brown, and striate. Colonies spread quickly across an agar surface, covering it with dense cottony growth that is first white and then turns gray or yellowish brown when sporulation occurs.

Rhizopus's structure
In the wild, they often grow quickly and primarily resemble cotton.

Rhizopuses are coenocytic plants with branching mycelium in their bodies. They also have branched mycelium, which is made up of three different kinds of hyphae (stolon, rhizoids, and sporangiophores) and is coenocytic in nature.

The stolon is an aerial structure that forms an arch and reaches the substratum to form the nodal region. It is found in the internodal region.

At nodes, rizoids are created as the stolon comes into contact with the substratum. In addition to absorbing food, they have branching and anchor the mycelium to the substratum.

In addition, a reproductive hyphae made up of sporangiophores rises vertically from the stolon. They produce sporangiospores, a type of reproductive structure, and are columellate, elongated, and unbranched. Below are the various components of hyphae:

Cell Wall: Proteins, lipids, chitosan, and other substances make up the cell wall.

Nuclei, mitochondria, endoplasmic reticulum, and other cytoplasmic inclusions such as ribosomes and oil droplets make up the protoplasm.

Columella: These primarily hygroscopic organisms are derived from u-shaped sporangiophores, and their primary job is to absorb water.

The sporangium serves as a mediator between the sporangiophore and the columella. Their shape is primarily spherical or globose. They also have sporangiospores, a reproductive component.

Sporangiospores: These spores are mostly unicellular in form and are known to be asexual.

Colonies are up to 10 mm high, dark greyish-brown, and produce simple rhizoids. Brownish in color, sporangiophores can grow up to 400 µm in height and 10 µm in width. They are typically generated in pairs or in groups of one to four. The round, greyish-black sporangia can have a diameter of up to 100 µm. Eighty percent of the sporangium is made up of globose, conical, and subglobose colonellae. The sporangiospores range in size from angular to broadly ellipsoidal or subglobose, with a length of up to 9 µm with a noticeable striation.Chlamydospores could exist. Zygospores have uneven suspensor cells and stellate projections. They are spherical, dark red-brown, and can have a diameter of up to 100 µm. Azygospores may be produced by homothallic strains. At 45°C, there is good growth, reaching a maximum of 50–52°C. 

• Sporangiophores originate from the rhizoidal node's upper side.
• The apical portion enlarges to create a sporangium, and cytoplasm and nuclei migrate apically.
• The cytoplasm of sporangium divides into two regions: the central columella region, which has fewer nuclei and more vacuoles, and the denser periphery region, which has more nuclei.
• Inside the sporangium, sporangiospores grow. They are non-motile and multinucleated.
• After maturation, the sporangium wall bursts, releasing the sporangiospores as a powdery mass.
• Upon receiving an appropriate environment and substrate, every spore develops into a new mycelium.

 

2. Formation of Chlamydospores: Unfavorable circumstances lead to the formation of Chlamydospores. Mycelium forms an intercalary segment as a result of septa formation and protoplasm buildup. It has robust walls and, after drying, separates from the mycelium. When favorable conditions return, they stay dormant and eventually germinate to produce new mycelium.

For sexual reproduction, two suitable hyphae fuse together. The majority of Rhizopus species, including R. stolonifer, are heterothallic, meaning that their mycelium differs for mating strains + and –. It is homothallic, R. sexualis.

The hyphae that are compatible unite. A little protrusion appears in both mycelia. We refer to it as progametangia.

Progametangia make contact with the apical region as nuclei and cytoplasm advance in that direction.
Septae development divides the apical area from the remaining hyphae. We call this gametangia.
A multinucleated structure is formed when gametangia conjugate.

• Karyogamy occurs after plastogamy, and a diploid (2n) zygote is produced. We call it zygospore. The remaining single nuclei decay
• Zygospores grow larger, have thick walls, and become resistant to unfavorable environmental factors. Zygospores germinate when favorable conditions are met.
• The zygospore's inner wall transforms into a promycelium, which forms the germ sporangiophore, and the germ sporangium forms apically.
• Haploid meiospores are produced as a result of meiosis. Following the breaking of the germ sporangium wall, they emerge as new mycelia. 

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