Agaricus bisporus is the scientific name of a familiar agricultural product. It is more commonly know as the white or button mushroom. The most familiar form of the mushroom is the harvested caps we see in the grocery store. However, there's more to this form of fungi than meets the eye.
Mycelial Growth Stage
The life of Agaricus bisporus begins with spores. Each spore has a germ pore, a circular indentation in one end of the spore. From this pore, a haploid strand called a hypha will grow. Spores will enter the growth medium (soil, logs, etc.) and the hypha will grow, branching to form mycelium, a web of cells beneath the surface of the ground.
Hypha Growth Stage
The hypha are haploid, meaning they have exactly half of the chromosomes necessary to form a mushroom. When two genetically compatible hypha come in contact, the cell walls of each hypha dissolve and fuse together, combining their genetic material into one cell. From then on, any growth from these cells will also contain two nuclei, and will be dikaryotic, having a full set of chromosomes. These cells continue to form mycelium. This mycelium, however, is now capable of forming the fruiting bodies that we commonly call mushrooms.
Fruit Body Stage
Most mushroom species, including A. bisporus, will take several weeks to grow fruiting bodies. Immediately before fruiting bodies develop, nuclei within the dikaryotic cells begin to replicate in large numbers. Then the cells will divide rapidly, forming the fruiting bodies. As they grow, they will erupt from the growth medium as a bud, eventually forming a mushroom. This is typically the stage in the life cycle of A.bisporus when they are harvested for human consumption.
Basidia Development Stage
As the mushroom matures, it will develop a stem and cap. Under the cap, gills will form. As the gills mature, bubble-like cells called basidia will grow in the gill slits. These cells have two nuclei. The nuclei will eventually merge to form a single diploid nucleus. This will then reproduce through meiosis to form four haploid daughter cells.
Spore Development Stage
Projections called sterigmatae will then develop. The nuclei within the daughter cells will then migrate through this growth and form four spores at the tip. The spores wait at the end of the sterigmata until they are physically dislodged. The spores are then released from the mushroom, falling to the ground to begin the life cycle again.