|Wednesday, 15 December 2010 19:49
Are fungi plants?
No. In biology they represent their own kingdom. They possess no chlorophyl and they reproduce themselves not by seeds, but by spores. What we call "mushrooms" are just the fruits of a large branched creature living in the ground, which is the actual fungus. You can compare it with an apple tree. The difference is that the mushroom-"tree" lives underground. For its reproduction the fungus stretches its fruits over the ground, in order to spread its spores.
How many different kinds of fungi are there?
The exact number of species of fungi will vary somewhat, depending upon which classification scheme is followed. Generally, however, it is estimated that there are about 60,000 valid species of fungi. Over 100 new species are described in the scientific literature each month, so the total number increases steadily. The British mycologist, David Hawksworth, however, has estimated that there may be as many as 1.5 million species of fungi. If true, this means that we have discovered only about 4% of the fungi that exist.
How Do Mushrooms Reproduce?
A Quick Analogy: A spore is much like a seed. It contains all of the genetic information that will grow and produce the fruit of the mushroom. The mushroom is the sex organ of the mushroom that will produce spores or "seeds".
The Definition: A spore is a nearly microscopic, sometimes single-celled reproductive body that is extremely resistant to desiccation and heat and is capable of growing into a new organism, produced especially by certain bacteria, fungi, algae, and nonflowering plants.
Mycelial Reproduction: When spores germinate (reproduce) a thread emerges from the spore casing. When two threads from different spore bodies intersect, they attempt to mate through a hook and clamp connection. A tiny pipe is opened between threads and genetic material is exchanged. The genetically complete threads become hyphae and begin to grow.
Spores have four combinations of sexes. Not all intersecting threads are able to mate. Not all matings will produce fertile mycelia.
Spores form as swellings on one or more subtending hypha in the soil or in roots. These structures contain lipids, cytoplasm and many nuclei. Spores usually develop thick walls with more than one layer and can function as propagules. Spores may be aggregated into groups called sporocarps. Sporocarps may contain specialized hyphae and can be encased in an outer layer (peridium). Spores apparently form when nutrients are remobilised from roots where associations are senescing. They function as storage structures, resting stages and propagules. Spores may form specialized germination structures, or hyphae may emerge through the subtending hyphae or grow directly through the wall.
A single spore contains a half set of chromosomes (known as haploid), much like any reproductive cell (ova or sperm). The spore has a protein sheath (the colored part that we can see) which encases the cell. When optimal conditions surround the spore, it will germinate. This is when it pushes its cellular mass through the protein sheath (at the germ pore) by expansion from re-absorbed water. This mass is a fine filament called the monokaryote (aka: the primary mycelium). It still has a half set of chromosomes. This monokaryote grows (still a single cell with a single nucleus) until it finds a compatible monokaryote to mate with. It does this by touching and dissolving its cell wall while the mate does the same. They effectively just merge to become one cell with 2 nuclei.
A Related Quote: "Asymmetric genome shuffling involves a fusion between a dikaryotic protoplast and a monokaryotic protoplast. Because only the cytoplasm of the monokaryon is inherited by the progeny, and one of either of the haplotypes of the dikaryon migrates into the progeny, the monokaryon is called a"recipient" and the dikaryon is called a "donor." Accordingly, the resulting fused dikaryotic progenies are heterokaryotic, but their cytoplasm is of the recipient monokaryon." (Tan)
Though the clamp connection serves a different function.
This is where things get strange. After the mating, the resultant cell can now reproduce by mitosis, but the cell still has 2 nuclei, as mentioned. So, when it mitoses, the 2 nuclei split for a total of 4 nuclei, but still only 2 cells. Speed of growth is much greater in these dikaryotic mycelial threads, because they don't have to stretch a single cell over a long gap. They simply split into more cells to spread.
Clamp connections form between 2 dikaryotic mycelial masses. This is how one of those little fuzzy white patches (aka mycelium) mates with the other white patches. The dikaryotic mycelia "clamps" together. Thus, reproduction is complete.