fungi reproduction: Fungi reproduce sexually and/or asexually. Perfect fungi reproduce both sexually and asexually, while imperfect fungi reproduce only asexually (by mitosis).
In both sexual and asexual reproduction, fungi produce spores that disperse from the parent organism by either floating on the wind or hitching a ride on an animal. Fungal spores are smaller and lighter than plant seeds. The giant puffball mushroom bursts open and releases trillions of spores. The huge number of spores released increases the likelihood of landing in an environment that will support growth.
Asexual reproduction in fungi:
Fungi reproduce asexually by fragmentation, budding, or producing spores. Fragments of hyphae can grow new colonies.
- fission of somatic cell
- Budding of somatic cell
- Fragmentation or disjoining of hyphae
- Asexual spore formation
1. Fission:
- It is characteristic of bacteria. In fungi, this occurs only in fission yeasts. The cell divides in transverse plane into two cells.
- In binary fission a mature cell elongates and its nucleus divides into two daughter nuclei.
- The daughter nuclei separates, cleaves cytoplasm centripetally in the middle till it divides parent protoplasm into two daughter protoplasm.
- A double cross wall is deposited in the middle to form two daughter cell.
- Ultimately the middle layer of double cross wall degenerates and daughter cells are separated.
- Examples: Saccharomyces pobbe, Psygosaccharomyces
2. Budding:
- The cell wall bulge out and softens in the area probably by certain enzymes brought by vesicles.
- The protoplasm also bulge out in this region as small protuberance.
- The parent nucleus also divides into two, one of the daughter nucleus migrates into bud, the cytoplasm of bud and mother remain continuous for some time
- As the bud enlarges, a septum is laid down at the joining of bud with mother cell. Then bud separates and leads independent life.
- Sometimes, budding is so quick that a chain of cells is formed due to non-detachment of the daughter cells.
- Budding is the typical reproductive characteristics of Ascomycetes.
- Examples: yeast
3. Fragmentation:
- A small bit of the broken hypha establishes a new colony. Fragmentation occurs in nature and is employed in the laboratory to keep the fungus growing by transferring small portions of hyphae to new culture tubes.
- In some fungi, fragmentation or disjoining of hyphae occurs and each hyphae become a new organism
4. Asexual spore of fungi:
- Spore formation is the characteristic feature of fungi.
Types of asexual spore:
i. Sporangiospore:
- These asexual spore are produced in a sac like structure called sporangia (singular;saprangium).
- Sporangium are produced at the end of special aerial hyphae called sporangiophore
- Sporangium contains large numbers of haploid spores, which are released by rapture of sporangial wall
- Examples: Rhizopus
ii. Conidiospore:
- Conidiospore or conidia are single celled, bicelled or multicelled structure born on the tip or side of aerial hyphal structure called conidiophore
- Conidia are different from sporangiospore as these are not produced inside sporangium or any sac like structure.
- Conidia are born singly or in chain
- Examples: Penicillium, Apergillus
iii. Arthrospore:
- Arthrospore are very primitive type of spore formed by the breaking up of fungal mycelium
- A spore is formed by separation followed by fragmentation of hyphae
- Examples: Trichosporium, Geotrichum, Coccididious imitis
iv. Chlamydospore:
- These are usually formed during unfavorable condition and are thick walled single celled spore, which are highly resistant to adverse condition.
- Hyphal cell or portion of hyphae contracts, loose water, round up and develops into thick walled chalmydospore.
- When favorable condition returns, each chlamydospore give rise to a new individual fungi.
- Examples: ascomycetes, basidiomycetes, zygomycetes,
- Histoplasma capsulatum, Candida albicans
v. Blastospore:
- It is a budding spores usually formed at the terminal end of hyphae.
- These spore may remains attached to hyphae and bud further to gibe branching chain of blastospores
- Examples: ascomycetes, basidiomycetes, zygomycetes
Sexual reproduction in fungi:
Sexual reproduction takes place by fusion of two nuclei originating from two individuals of opposite mating types, generally designated as male and female. Fusion of the nuclei is preceded by fusion of two protoplasts; the process is called plasmogamy.
Fusion of the nuclei is known as karyogamy. It leads to production of a diploid cell, called zygote. Eventually, meiosis takes place to restore the hyploid cells. In the higher fungi, i.e. in ascomycetes and basidiomycetes, karyogamy does not follow plasmogamy immediately.
Rather, the pair of nuclei divides synchronously to produce a dicaryophase. Ultimately, the two nuclei fuse to produce a diploid nucleus in a few cells before production of ascospores and basidiospores. The diploid nucleus undergoes meiosis immediately to produce haploid nuclei which pass into the ascospores and basidiospores.
Various methods by which compatible nuclei are brought together in plasmogamy. Some are:
- Gametic copulation
- Gamete-gametangial copulation
- Gametangial copulation
- Somatic copulation
- Spermatization
1. Gametic copulation:
In lower fungi, such as chytrids, sexual reproduction takes place by fusion of male and female gametes. The male and female gametes may be morphologically similar (isogamy) or dissimilar (anisogamy). One or both gametes may be motile or non-motile (aplanogamy).
Fusion of two naked gametes, one or both of them are motile
- Isogamous
- Anisogamous
- Oogamous
2. Gamete-gametangial copulation:
In many phycomycetes, such as Saprolegnia, sexual reproduction is effected by gametangial contact. A gametangium is the structure in which gametes are formed. The male and female gametangia come in contact and a pore is produced at the point of contact. The male gametes (nuclei) pass through the pore into the female gametangium where they fertilize the eggs or oospheres to produce diploid oospores
Male and female gametangia comes into contact but do not fuse.
A fertilization tube formed from where male gametangium enters the female gametangium and male gamate passes through this tube
3. Gametangial copulation:
In the zygomycetes, such as Mucor, the male and female gametangia come in contact and the entire gametangia fuse with other. Thereby, their separate identity is lost and the fusion produces a zygospore. In the zygospore, the male and female nuclei pair with each other. Eventually, some of these pairs of nuclei fuse and the diploid nuclei undergo meiosis to restore haploidy.
4. Somatic copulation:
In higher basidiomycetes, like mushrooms, specialized sex organs are totally absent. In these fungi, male and female nuclei are brought together by fusion of vegetative hyphae originating from mycelia of opposite mating types.
Also known as somatogamy.
In this process fusion of somatic cell occurs
This sexual fusion of undifferentiated vegetative cell results in dikaryotic hyphae, so the process is also called dikarotization
5. Spermetization:
In some basidiomycetes, such as the rust-fungus Puccinia, the male gametes are called spermatia which are produced in pycnidia (or spermogonia). The uninucleate non-motile spermatia are passively transferred by insects to the receptive female hyphae leading to plasmogamy. The male nucleus passes into the female receptive hypha and fuse with a female nucleus.
It is an union of special male structure called spertatium with a female receptive structure.
Spermatium empties its content into receptive hyphae during plasmogamy
Sexual spores of fungi
- As a result of sexual reproduction sexual sores are produced.
- Sexual spores are fewer in number than asexual spores.
Types of sexual spores
i. Ascospore:
- It is usually single celled produced in a sac called ascus (plural;asci) and usually there are 4-8 ascospore in an ascus but the number may vary from species to species
- The ascospore are usually arranged in a linear order. In some case ascospores are long, narrow and are arranged in parallel order.
ii. Basidiospore:
- It is a reproductive spore produced by basidiomycetes.
- This single celled spores are born in a club shaped structure called basidium
- These basidiospore aerves as main air dispersal unit for the fungi.
iii. Zygospore:
- Zygospores are thick walled spores formed when two sexually compatible hyphae or gametangia of certain fungi fuse together.
- In suitable condition, zygospore germinates to produce a single vertical hyphae which forms a aporangium and releases its spores
iv. Oospore:
- These are formed within a special female structure called Oogonium.
- Fertilization of egg by male gamete in female sex organ give rise to oospoes.
- There are one or more oospores in each oogonium.
