As part of s*xual reproduction, fungi undergo plasmogamy, in which the protoplasm of two-parent cells (usually from the mycelia) fuse together without merging the nuclei, effectively bringing together two haploid nuclei in one cell. Karyogamy occurs next, where the two nuclei fuse together and undergo meiosis to produce spores.
It is not uncommon for fungi to remain in dikaryotic states for many generations after plasmogamy before they undergo karyogamy. Plasmogamy is usually followed immediately by karyogamy in lower fungi. An analysis of comparative genomics demonstrated that plasmogamy, karyogamy, and meiosis machinery are present in the Amoebozoa.
What is Plasmogamy?
Plasmogamy occurs when the two cytoplasms of haploid gametes are united during syngamy in fungi. Cell fusion occurs after the fusion of the two nuclei. Nevertheless, by plasmogamy, two haploid nuclei are brought closer together within a cell in order to merge. Plasmogamy is followed by a dikaryotic stage, which can last for several generations before being replaced by karyogamy.
A heterothallic organism consists of two different types of thalli fusing together. In Basidiomycota, heterothallism is evident. Is a haploid parent cell and two hyphal protoplasts are united within the mycelia of Basidiomycotina. For several generations, a single cell consists of two haploid nuclei (dikaryon). These cells undergo cell division and growth during dikaryon.
The two main types of plasmogamy in lower fungi are planogametic copulation and gametangial contact. It is known that Chytridiomycetes and Plasmodiophoromycetes copulate with mobile gametes.
Oomycetes, like fungi, produce non-motile gametes called aplanogametes during gametangial contact. A lower fungus-like Mucorales can fuse gametangia by means of gametangial copulation. Homothallism is an alternative means of s*xual reproduction for fungi, in which one thallus fuses with another of the same species.
What is Karyogamy?
During the syngamy of fungi, a dikaryotic cell’s nuclei are fused together. This process is known as karyogamy. Karayogamy is the final step in the syngamy process. A haploid nucleus’ nuclear envelope is fused three times during karyogamy. In the first step, the two nuclei’s outer membranes are fused together.
After undergoing the karyogamy, the dikaryotic cell becomes diploid. The resultant diploid cells are known as zygotes or zygospores. The zygote is the only diploid phase found in the fungal life cycle. Karyogmy is followed by meiosis in diploid cells. When a cell divides, it produces four daughter cells, each a haploid, by duplicating chromosomes and recombining genetic material.
Consequently, karyogamy contributes to genetic variation within the fungus population. To increase the number of cells, daughter cells undergo mitosis. They are known as spores. Haployd spores are produced as a result of s*xual reproduction in fungi.
Ascomycetes and Basidiomycetes have delayed karyogamy and the dikaryokitc cells persist over several generations. Dikaryotes are capable of mitotic division as well as conventional cytokinesis. A fungus’ dikaryotic phase is known as the growth phase. As the mycelium develops, the two dikaryotic nuclei are divided simultaneously into two daughter cells, resulting in the development of the mycelium and dikaryotic. The karyogamy, however, occurs immediately after the plasmogamy in lower fungi, such as Phycomycetes.
Plasmogamy vs Karyogamy
Fungi engage in both plasmogamy and karyogamy simultaneously. Syngamy refers to the s*xual reproduction of fungi, which is a method of recombination. The forming diploid nucleus undergoes plasmogamy, then karyogamy, and then mitotic division. Lower fungi undergo plasmogamy when their cytoplasms merge. It is also possible for the two oppositely mating types of fungal thalli to fuse together, forming the diksryotic cell stages, as well.
Lower-level fungi undergo either plasmogamy or karyogamy. Higher fungi maintain the dikaryotic stage of cells by delaying karyogamy for several generations. Karyogamy is essentially the fusion of two haploid nuclei in fungi, whereas plasmogamy is the fusion of two hyphal protoplasts.
Differences on the basis of various factors:
Plasmogamy: Plasmogamy occurs when two hyphal protoplasts fuse.
Karyogamy: In fungi, karyogamy occurs when two haploid nuclei fuse.
Plasmogamy: The first step in syngamy in fungi is plasmogamy.
Karyogamy: The second stage of syngamy is karyogamy.
Plasmogamy: Plasmogamy produces a dikaryotic cell.
Karyogamy: Karyogamy produces a cell containing a diploid nucleus.
Number of Nuclei
Plasmogamy: Plasmogamy generates a cell containing two haploid nuclei.
Karyogamy: Karyogamy generates a cell containing a single diploid nucleus.
Plasmogamy: Plasmogamy is followed by karyogamy.
Karyogamy: Karyogamy is followed by meiosis.
Key Points to Remember
- The fragmentation of hyphae can lead to the growth of new colonies of fungi.
- When a cell buds, a bulge forms on its side. The bud eventually detaches after the nucleus divides mitotically.
- As*xual spores are genetically identical to their parents and maybe released either outside or within a special reproductive sac called a sporangium.
- S*xual reproduction in fungi often occurs as a result of adverse environmental conditions.
- S*xually reproducing mycelium can be homothallic or heterothallic.
- The three stages of fungus s*xual reproduction are plasmogamy, karyogamy, and gametangia.
Key Terms to Remember
- Homothallic: male and female reproductive structures are present in the same plant or fungal mycelium
- Gametangium: an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants
- Spore: a reproductive particle, usually a single cell, released by a fungus, alga, or plant that may germinate into another
- Sporangium: a case, capsule, or container in which spores are produced by an organism
- Karyogamy: the fusion of two nuclei within a cell
- Plasmogamy: stage of s*xual reproduction joining the cytoplasm of two-parent mycelia without the fusion of nuclei
During syngamy in fungi, both occur. Syngamy is a type of recombination, considered as the s*xual reproduction of fungi. Karayogamy follows Plasmogamy. The fusion of two protoplasts of either gamete of different types of thalli occurs in plasmogamy. The haploid cells formed by plasmogamy are called dikaryons since they have two haploid nuclei. These dikaryotic stages are maintained for a number of generations in higher fungi such as Basidiomycota.
In lower fungi, however, plasmogamy is immediately followed by karyogamy. Karyogamy occurs when two haploid nuclei fuse together in the dikaryotic cell. Plasmogamy occurs in Basidiomycetes when two mating types of thalli form a pair. Developing dikaryotic thallus from the basidiocarp, which is a characteristically large fruiting body. During the syngamy process, two gametes fuse in lower fungi such as Oomycota.
During meiosis, a diploid nucleus can be produced by karyogamy between the two haploid nuclei. Mycelium produced by haploid pores germinates. Their structures, which are easily fused, are the primary difference between plasmogamy and karyogamy.