Aspergillus oryzae is used in the fermentation of rice to produce sake. Other ascomycetes parasitize plants and animals, including humans. For example, fungal pneumonia poses a significant threat to AIDS patients who have a compromised immune system. Ascomycetes not only infest and destroy crops directly; they also produce poisonous secondary metabolites that make crops unfit for consumption. Filamentous ascomycetes produce hyphae divided by perforated septa, allowing streaming of cytoplasm from one cell to the other.
Conidia and asci, which are used respectively for asexual and sexual reproductions, are usually separated from the vegetative hyphae by blocked non-perforated septa. Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores [link]. Sexual reproduction starts with the development of special hyphae from either one of two types of mating strains [link].
At fertilization, the antheridium and the ascogonium combine in plasmogamy without nuclear fusion. In each ascus, two or more haploid ascospores fuse their nuclei in karyogamy. During sexual reproduction, thousands of asci fill a fruiting body called the ascocarp.
The diploid nucleus gives rise to haploid nuclei by meiosis. The ascospores are then released, germinate, and form hyphae that are disseminated in the environment and start new mycelia [link]. The fungi in the Phylum Basidiomycota are easily recognizable under a light microscope by their club-shaped fruiting bodies called basidia singular, basidium , which are the swollen terminal cell of a hypha. The basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom, commonly seen in fields after rain, on the supermarket shelves, and growing on your lawn [link].
This group also includes shelf fungus, which cling to the bark of trees like small shelves. In addition, the basidiomycota includes smuts and rusts, which are important plant pathogens; toadstools, and shelf fungi stacked on tree trunks. Most edible fungi belong to the Phylum Basidiomycota; however, some basidiomycetes produce deadly toxins. For example, Cryptococcus neoformans causes severe respiratory illness. The lifecycle of basidiomycetes includes alternation of generations [link].
Spores are generally produced through sexual reproduction, rather than asexual reproduction. The club-shaped basidium carries spores called basidiospores. In the basidium, nuclei of two different mating strains fuse karyogamy , giving rise to a diploid zygote that then undergoes meiosis. The haploid nuclei migrate into basidiospores, which germinate and generate monokaryotic hyphae. The mycelium that results is called a primary mycelium. Mycelia of different mating strains can combine and produce a secondary mycelium that contains haploid nuclei of two different mating strains.
This is the dikaryotic stage of the basidiomyces lifecyle and and it is the dominant stage. Eventually, the secondary mycelium generates a basidiocarp , which is a fruiting body that protrudes from the ground—this is what we think of as a mushroom. The basidiocarp bears the developing basidia on the gills under its cap. While Deuteromycota use to be a classification group, recent moleclular analysis has shown that the members classified in this group belong to the Ascomycota or the Basidiomycota classifications.
Since they do not possess the sexual structures that are used to classify other fungi, they are less well described in comparison to other members. Most members live on land, with a few aquatic exceptions. They form visible mycelia with a fuzzy appearance and are commonly known as mold. Reproduction of the fungi in this group is strictly asexual and occurs mostly by production of asexual conidiospores [link].
Some hyphae may recombine and form heterokaryotic hyphae. Genetic recombination is known to take place between the different nuclei. The fungi in this group have a large impact on everyday human life. The food industry relies on them for ripening some cheeses.
The blue veins in Roquefort cheese and the white crust on Camembert are the result of fungal growth. The antibiotic penicillin was originally discovered on an overgrown Petri plate, on which a colony of Penicillium fungi killed the bacterial growth surrounding it.
Other fungi in this group cause serious diseases, either directly as parasites which infect both plants and humans , or as producers of potent toxic compounds, as seen in the aflatoxins released by fungi of the genus Aspergillus. The Glomeromycota is a newly established phylum which comprises about species that all live in close association with the roots of trees. Fossil records indicate that trees and their root symbionts share a long evolutionary history. It appears that all members of this family form arbuscular mycorrhizae : the hyphae interact with the root cells forming a mutually beneficial association where the plants supply the carbon source and energy in the form of carbohydrates to the fungus, and the fungus supplies essential minerals from the soil to the plant.
The glomeromycetes do not reproduce sexually and do not survive without the presence of plant roots. Although they have coenocytic hyphae like the zygomycetes, they do not form zygospores. What type of fungus is this? Classification of Fungi For a long time, scientists considered fungi to be members of the plant kingdom because they have obvious similarities with plants. The Kingdom Fungi Today, fungi are no longer classified as plants. Fungal Phyla Classification of fungi below the level of the kingdom is controversial.
Summary Fungi used to be classified as plants. Now, they are known to have unique traits that set them apart from plants. For example, fungal cell walls contain chitin, not cellulose, and fungi absorb food rather than make their own. Below the level of the kingdom, classification of fungi is controversial. Review State why fungi were once classified as plants. When the zygospore germinates, it undergoes meiosis and produces haploid spores, which will, in turn, grow into a new organism.
Figure 2. Zygomycetes have asexual and asexual life cycles. In the sexual life cycle, plus and minus mating types conjugate to form a zygosporangium. Figure 3. Sporangia grow at the end of stalks, which appear as a white fuzz seen on this bread mold, Rhizopus stolonifer. The b tips of bread mold are the spore-containing sporangia.
The majority of known fungi belong to the Phylum Ascomycota , which is characterized by the formation of an ascus plural, asci , a sac-like structure that contains haploid ascospores. Many ascomycetes are of commercial importance. Some play a beneficial role, such as the yeasts used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies. Aspergillus oryzae is used in the fermentation of rice to produce sake. Other ascomycetes parasitize plants and animals, including humans.
For example, fungal pneumonia poses a significant threat to AIDS patients who have a compromised immune system. Ascomycetes not only infest and destroy crops directly; they also produce poisonous secondary metabolites that make crops unfit for consumption. Filamentous ascomycetes produce hyphae divided by perforated septa, allowing streaming of cytoplasm from one cell to the other.
Conidia and asci, which are used respectively for asexual and sexual reproductions, are usually separated from the vegetative hyphae by blocked non-perforated septa. Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores Figure.
Sexual reproduction starts with the development of special hyphae from either one of two types of mating strains Figure. At fertilization, the antheridium and the ascogonium combine in plasmogamy without nuclear fusion.
In each ascus, two or more haploid ascospores fuse their nuclei in karyogamy. During sexual reproduction, thousands of asci fill a fruiting body called the ascocarp. The diploid nucleus gives rise to haploid nuclei by meiosis. The ascospores are then released, germinate, and form hyphae that are disseminated in the environment and start new mycelia Figure.
Figure 4. The lifecycle of an ascomycete is characterized by the production of asci during the sexual phase. The haploid phase is the predominant phase of the life cycle. Figure 5. The bright field light micrograph shows ascospores being released from asci in the fungus Talaromyces flavus var.
The fungi in the Phylum Basidiomycota are easily recognizable under a light microscope by their club-shaped fruiting bodies called basidia singular, basidium , which are the swollen terminal cell of a hypha. The basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom, commonly seen in fields after rain, on the supermarket shelves, and growing on your lawn Figure 6.
This group also includes shelf fungus, which cling to the bark of trees like small shelves. In addition, the basidiomycota includes smuts and rusts, which are important plant pathogens; toadstools, and shelf fungi stacked on tree trunks. Most edible fungi belong to the Phylum Basidiomycota; however, some basidiomycetes produce deadly toxins. For example, Cryptococcus neoformans causes severe respiratory illness.
Figure 6. The body of this fungus, its mycelium, is underground and grows outward in a circle. The lifecycle of basidiomycetes includes alternation of generations Figure 7.
Spores are generally produced through sexual reproduction, rather than asexual reproduction. The club-shaped basidium carries spores called basidiospores. In the basidium, nuclei of two different mating strains fuse karyogamy , giving rise to a diploid zygote that then undergoes meiosis. The haploid nuclei migrate into basidiospores, which germinate and generate monokaryotic hyphae. The mycelium that results is called a primary mycelium.
Mycelia of different mating strains can combine and produce a secondary mycelium that contains haploid nuclei of two different mating strains. This is the dikaryotic stage of the basidiomyces lifecyle and and it is the dominant stage.
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