Fungi

1. Fungi (pgs. 548-559)

2. Table Of Contents Hyphae Basidia Mycorrhizae Conidium Mycelium

3. Hyphae • A hypha (plural hyphae) is a long, branching filamentous cell of a fungus, and also of unrelated Actinobacteria. In fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Continue For More information on Hyphae Continue To Basidia

4. Hyphae • Generativehyphae are relatively undifferentiated and can develop reproductive structures. They are typically thin-walled, occasionally developing slightly thickened walls, usually have frequent septa, and may or may not have clamp connections. They may be embedded in mucilage or gelatinized materials. • Skeletalhyphae are of two basic types, the classical form is thick-walled and very long in comparison to the frequently septate generative hyphae, unbranched or rarely branched, with little cell content. They have few septa and lack clamp connections. • Fusiform skeletalhyphae are the second form of skeletal hyphae. Unlike typical skeletal hyphae these are swollen centrally and often exceedingly broad, hence giving the hypha afusiform shape. • Bindinghyphae are thick-walled and frequent branched. Often they resemble deer antlers or defoliated trees because of the many tapering branches. Go to Basidia

5. Basidia Continue to More on Basidia Back to Hyphae • A basidium (pl., basidia) is a microscopic, spore-producing structure found on the hymenophore of fruiting bodies of basidiomycete fungi. The presence of basidia is one of the main characteristic features of the Basidiomycota. A basidium usually bears four sexual spores called basidiospores; occasionally the number may be two or even eight. In a typical basidium, each basidiospore is borne at the tip of a narrow prong or horn called a sterigma (pl. sterigmata), and is forcibly discharged upon maturity. • The word basidium literally means little pedestal, from the way in which the basidium supports the spores. However, some biologists suggest that the structure more closely resembles a club. An immature basidium is known as a basidiole.

6. Basidia Continue to Mychorrhiza • Most basidiomycetes have single celled basidia (holobasidia), but in some groups basidia can be multicellular (a phragmobasidia). For instance, rust fungi in the order Uredinales have four-celled phragmobasidia that are transversely septate; some jelly fungi in the order Tremellales have four-celled phragmobasidia that are cruciatelyseptate. Sometimes the basidium (metabasidium) develops from a probasidium, which is a specialized cell which is not elongated like a typical hypha. The basidium may be stalked or sessile.

7. Mycorrhizae More on Mycorrhiza • A mycorrhiza (Greek for fungus roots coined by Frank, 1885[1]; typically seen in the plural forms mycorrhizae or mycorrhizas) is a symbiotic (occasionally weakly pathogenic) association between a fungus and the roots of a plant.[2] In a mycorrhizal association, the fungus may colonize the roots of a host plant, either intracellularly or extracellularly. It is an important part ofsoil life. • This mutualistic association provides the fungus with relatively constant and direct access to mono- or dimericcarbohydrates, such as glucose and sucrose produced by the plant inphotosynthesis.[3] The carbohydrates are translocated from their source location (usually leaves) to the root tissues and then to the fungal partners. In return, the plant gains the use of themycelium's very large surface area to absorb water and mineral nutrients from the soil, thus improving the mineral absorption capabilities of the plant roots.[4] Plant roots alone may be incapable of taking up phosphateions that are immobilized, for example, in soils with a basic pH. The mycelium of the mycorrhizal fungus can however access these phosphorus sources, and make them available to the plants they colonize.[5] The mechanisms of increased absorption are both physical and chemical. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and can explore a greater volume of soil, providing a larger surface area for absorption. Also, the cell membrane chemistry of fungi is different from that of plants. Mycorrhizae are especially beneficial for the plant partner in nutrient-poor soils.

8. Mycorrhizae Continue to Conidium • Mycorrhizal plants are often more resistant to diseases, such as those caused by microbial soil-borne pathogens, and are also more resistant to the effects of drought. These effects are perhaps due to the improved water and mineral uptake in mycorrhizal plants. • Mycorrhizae form a mutualistic relationship with the roots of most plant species (and while only a small proportion of all species has been examined, 95% of these plant families are predominantly mycorrhizal).[6]

9. Conidium Continue for more on Conidium • Conidia, sometimes termed conidiospores, are asexual,non-motile spores of a fungus; they are also called mitospores due to the way they are generated through the cellular process of mitosis. They are haploid cells genetically identical to the haploid parent, can develop into a new organism if conditions are favorable, and serve in biological dispersal. • Asexual reproduction in Ascomycetes (the Phylum Ascomycota) is by the formation of conidia, which are borne on specialized stalks calledconidiophores. The morphology of these specialized conidiophores is often distinctive of a specific species and can therefore be used in identification of the species. • The terms "microconidia" and "macroconidia" are sometimes used.

10. Conidium Continue for more on Conidium • There are two main types of conidium development. • blastic conidiogenesis, where the spore is already evident before it separates from the conidiogenic hypha which is giving rise to it, and • thallic conidiogenesis, where first a cross-wall appears and then the thus created cell develops into a spore.

11. Conidium Continue to Mycelium • A conidium may form germ tubes (germination tubes) and conidial anastomosis tubes (CATs) in specific conditions. These two are some of the specialized Hyphae that are formed by fungal conidia. Conidial anastomosis tubes are morphologically and physiologically distinct from germ tubes and are under separate genetic control. The biology of conidial anastomosis tubes is not completely understood. After conidia are induced to form conidial anastomosis tubes, they grow homing toward each other, and eventually they fuse. Once fusion happens, the nuclei can pass through fused CATs. These are events of fungal vegetative growth and not sexual reproduction. Fusion between these cells seems to be important for some fungi during early stages of colony establishment. The production of these cells has been suggested to occur in 73 different species of fungi.

12. Mycelium Continue for More on Mycelium • Mycelium (plural mycelia) is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or in many other substrates. Typically a single spore germinates into a monokaryotic mycelium which cannot reproduce sexually; when two compatible monokaryotic mycelia join and form a dikaryotic mycelium, that mycelium may form fruiting bodies such as mushrooms. A mycelium may be minute, forming a colony that is too small to see, or it may be extensive

13. Mycelium • One of the primary roles of fungi in an ecosystem is to decompose organic compounds. Petroleum products and pesticides that can be contaminants of soil are organic molecules. Fungi therefore should have potential to remove such pollutants from the soil environment, a process known as bioremediation. • Mycelial mats have been suggested (see Paul Stamets) as having potential as biological filters, removing chemicals and microorganisms from soil and water. The use of fungal mycelia to accomplish this has been termed "mycofiltration", although there is no reason to suspect that the process is any different from that of bioremediation using fungi. • Some Mycelium has symbiotic property with many plants. This opens the door to soil supplementation to improve crop yields. • Mycelium, spread on logging roads acts as a binder holding new soil in place and preventing washouts until woody plants can be established.

14. Terms: • Sporangia: A sporangium (pl., sporangia) is a plant, fungal, or algal structure producing and containing spores . • Rhizoids: Rhizoids are a structure in plants, fungi and some other organisms (e.g. some sponges) that functions like a root in support or absorption. • Stolons: Stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animalstolons are external skeletons.