Question

In which class of fungi karyogamy is delayed for a long time?

Answer 1

Fungi:

1. These are heterotrophic organisms with a great diversity of habitat and morphology.
2. These can be saprotrophs, parasitic and symbiotic based on their dependence on resources.
3. Some unicellular fungi like yeast are used in the bakery and brewery industry and some are disease-causing like Puccinia.

Classes of fungi:

Based on the morphology of mycelium, mode of spore formation, and fruiting bodies they are divided as-

1. Phycomycetes- aseptate and coenocytic mycelium is found. These reproduce asexually by zoospores (motile) or by aplanospores (non-motile). Zygospore is the resultant of two gametes. Gametes can be isogamous or anisogamous. Example: Rhizopus.
2. Ascomycetes- branched and septate mycelium is found. These reproduce asexually by conidia and sexually by ascospores which are arranged in fruiting bodies called ascocarps. Example: Penicillium, Aspergillus.
3. Basidiomycetes- branched and septate mycelium is found. Asexual spores are absent but produced vegetatively by fragmentation. The absence of sex organs is observed but plasmogamy is brought by the fusion of vegetative or somatic cells of different strains. Its fruiting bodies are called basidiocarps. Example: Puccinia, Ustilago.
4. Deuteromycetes- are also known as imperfect fungi because only asexual and vegetative phases are known. As soon as sexual phases are discovered they are moved into other classes. Example: Trichoderma, Alternaria.

Karyogamy:

1. Defined as the fusion of haploid cell nuclei to form resulting diploid cell nuclei.
2. The cell formed by karyogamy is called a zygote.
3. This process is immediately followed by meiosis.

Delayed karyogamy :

1. When plasmogamy is not followed by karyogamy and halted at a dikaryon stage ( n+n stage) is delayed karyogamy.
2. It is delayed for a longer period in basidiomycetes. The dikaryotic phase may even last for years
3. In basidiomycetes, plasmogamy is bought by the fusion of two vegetative gametes or somatic cells of different genotypes which gives rise to a dikaryotic structure.
4. This dikaryotic stage gets halted for a longer period may be years which will ultimately give rise to basidium.
5. Basidium undergoes karyogamy followed by meiosis to exogenously produce four basidiospores. Some common basidiomycetes are Ustilago and Puccinia.