Question

Which of the following produces a dikaryotic phase in Basidiomycetes?
A. Karyogany
B. Plasmogamy
с. Apogamy
D. Karyokinesis​

Answer 1

Answer:

Skip to main content

Lumen

Biology for Majors II

Module 6: Fungi

Basidiomycota: The Club Fungi

Photo shows toadstools growing in a ring on a lawn.

Figure 1. The fruiting bodies of a basidiomycete form a ring in a meadow, commonly called “fairy ring.” (Credit: “Cropcircles”/Wikipedia Commons)]

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. The fruiting bodies of a basidiomycete form a ring in a meadow, commonly called “fairy ring” (Figure 1). The best-known fairy ring fungus has the scientific name Marasmius oreades. The body of this fungus, its mycelium, is underground and grows outward in a circle. As it grows, the mycelium depletes the soil of nitrogen, causing the mycelia to grow away from the center and leading to the “fairy ring” of fruiting bodies where there is adequate soil nitrogen.

These mushroom-producing basidiomyces are sometimes referred to as “gill fungi” because of the presence of gill-like structures on the underside of the cap. The “gills” are actually compacted hyphae on which the basidia are borne. 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, and toadstools. 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 (Figure 2). 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.

The life cycle of basidiomycetes, better known as mushrooms, is shown. Basidiomycetes have a sexual life cycle that begins with the germination of 1n basidiospores into mycelia with plus and minus mating types. In a process called plasmogamy, the plus and minus mycelia form a dikaryotic mycelium. Under the right conditions, the dikaryotic mycelium grows into a basdiocarp, or mushroom. Gills on the underside of the mushroom cap contain cells called basidia. The basidia undergo karyogamy to form a 2n zygote. The zygote undergoes meiosis to form cells with four haploid (1n) nuclei. Cell division results in four basidiospores. Dispersal and germination of basidiospores ends the cycle.

Figure 2. The lifecycle of a basidiomycete alternates generation with a prolonged stage in which two nuclei (dikaryon) are present in the hyphae.

PRACTICE QUESTION

Which of the following statements is true?

A basidium is the fruiting body of a mushroom-producing fungus, and it forms four basidiocarps.

The result of the plasmogamy step is four basidiospores.

Karyogamy results directly in the formation of mycelia.

A basidiocarp is the fruiting body of a mushroom-producing fungus.

Show Answer

LICENSES AND ATTRIBUTIONS

PreviousNext

Footer Logo Lumen Waymaker

Answer 2

Answer:

B. Plasmogamy produces a dikaryotic phase in Basidiomycetes.

Explanation:

• Sexual reproduction in fungus involves the formation and the union of two gametes or their nuclei.

• In Heterothallic (different) forms, sexual reproduction involves fusion between two genetically different mating types.
• In Homothallic forms, fusion occurs between genetically similar types. Fusion involves the union of cytoplasms as well as nuclei. The former is called Plasmogamy while the latter is called Karyogamy.

• In higher fungi, karyogamy is delayed and occurs just before meiosis.

The mycelium of basidiomycete fungi pass through 3 distinct stages:

• 1. First stage or primary mycelium or homokaryon
• 2. Second stage or secondary mycelium: The cell of mycelium is binucleate and is represented as the dikaryo phase.
• 3. Third phase or tertiary mycelium.
• In the stage intervening between plasmogamy and karyogamy the cells often contain two nuclei or Dikaryons (n+n). Such cells are called dikaryotic cells.
• The particular phase is known as Dikaryophase which takes place in  Basidiomycetes.

• In such fungi, the life cycle is completed in three phases instead of two Haplophase, Dikaryophase and Diplophase (2n) and Meiosis occurs in diplophase.
• Thus it is the plasmogamy that produces the dikaryotic phase.

#SPJ2