Fungal Reproduction

state while the reproductive state is the fruiting body state. There are cases where the vegetative state can be quite large—in one case, a single organism covers more than 2,000 acres of hyphae.

Fungi are considered heterotrophs that live off of other organic compounds. Many are saprophytic, meaning they live off of dead or dying organisms. They don’t fix carbon dioxide in photosynthesis and they don’t fix nitrogen from the atmosphere. They do not ingest and then digest, like animals and many other organisms. Instead, they do the opposite. They send out exoenzymes outside of the hyphae that process the food outside of the organism. Then they absorb the smaller molecules. These exoenzymes will be able to break down the cellulose and lignan of plant cells. Similar to animals, their storage molecule is glycogen rather than starch.

FUNGAL REPRODUCTION

There are many ways that fungi can reproduce asexually, including budding, fragmentation, and spore formation. Sexual reproduction can also occur. The so-called perfect fungi can reproduce both sexually and asexually, while the “imperfect fungi” can only reproduce through mitosis. They do not undergo binary fission.

Spores can be produced and can be dispersed through other animals or the wind. These spores tend to be lighter and much smaller than plant seeds with trillions of spores released at one time in certain species. This huge number of spores will ensure that some of them will find the right habitat in order to start hyphal growth again.

Asexual fungal reproduction can be through budding, spore formation, or fragmentation. Fragmentation involves the breaking off of a hypha from the main mycelium. Yeast cells will bud off in a sort of cytokinesis process with mitosis occurring to send a copy of the genome to the daughter cell. The most common asexual reproductive strategy is through spore formation. One parent will make spores that will be genetically identical to the parent organism. The spores can be released from the parent thallus or can make a sporangium, which is a special reproductive sac. Figure 47 shows the fungi life cycle:

In the fungi life cycle, there are spores that are given off from the hyphae through mitosis and spore formation. The mycelium is a haploid structure with germination happening when the habitat is right. In the process of plasmogamy, two different mycelia will combine to form a diploid organism with two or more nuclei. In karyogamy, the nuclei fuse to make a true diploid organism. This makes a diploid zygote that undergoes meiosis to make a haploid organism and haploid cells that develop into another haploid mycelium. Sexual reproduction generally happens under the conditions of increased stress.

The mating of hyphae can be homothallic or heterothallic. Homothallic reproduction happens within the same mycelium, while heterothallic reproduction happens when two mycelia in close proximity to one another that are genetically compatible combine sexually.