Mycology – Study of Fungi
It is a branch of Botany which deals with the study of Fungi. Fungi are a cryptogamic group of plants placed under the division of Thalophyta.
Word Mycology was derived from the Greek word Mycos meaning mushroom and logy meaning study/thinking.
The systematic study of Fungi started during the seventeenth century with the discovery of the microscope. Using a microscope not only multicellular Fungi were studied comprehensively but also microscopic Fungi were also studied. The microscopic study has lead to the discovery of some 80,000 species of fungi (Alexopoulos, 1964).
Definition of Fungi (Fungus—Singular):
Biologists use term “Fungus” which include nucleated, spore-bearing, achlorophyllous organism which generally reproduces sexually as well as the asexually whose filamentous, branched and somatic structure is typically surrounded by a well-developed cell wall containing cellulose or chitin or both.
Importance of Fungi:
Fungi are an important group of plants which due to its some peculiar and distinctive characteristics/properties are socially, economically, environmentally, ecologically and more generally speaking biologically and industrially important.
To clarify their economical, biological and other importance some of there discussed below:
Decomposers are an important part of the biosphere. Decomposers are a part of the biotic component of an ecosystem. Fungi are one of the decomposers.
The decomposing process consists of decaying of the dead body of living being due to the extracellular activity of fungal enzymes secreted by it on the body of dead material. These enzymes digest the dead body. The digestion of dead body not only provides nutritional requirements to fungi and also release nutrients and elements/compounds putting them in the recycling process.
This maintains the ecological balance of nutrients in ecosystem/ all saprophytic and facultative fungi carry out this process of decomposition.
As Study / Research Tools
Many researchers/studies fail and are not put to the destination due to the large span of study and research in biological sciences. Fungi as an important tool in this scenario because of their short lifespan, fast growth and occupy less space.
Therefore, fungi are easy to study/research and get the result in a short time. These results are met with very soon for beneficial purposes for the service of mankind in many ways.
For example, Neurospora (A Fungus) was used to carry out experiments on the subject of inheritance in genetic sciences and results were experimentally verified, tested and applied for generalization and understanding the relevant phenomenon.
Laws of inheritance were studied and still valid all over the world and for all species of plants of all the groups.
As Destructive Tools
The destructive characteristics of fungi can be discussed under the following heads because of fungi’s mode of nutrition and secretion of some toxic agents:
- Spoilage of consumables/useable i.e. vegetables, fruits, food, cooked materials and wood materials are not only spoiled but destroyed as well.
- Fungi cause diseases in plants and animals especially in Agricultural crops i.e. rust, smut and in Forestry causing different diseases in trees i.e. in Junipers, Conifers, and other valuable trees.
- Spoilage and destruction of other materials of common use in our daily life i.e. plastics (by Pennicillia, Aspergilli), cold creams, vanishing creams, lotion, foundation creams, baby oils and other cosmetics etc.
- Human diseases caused by fungi are Athlete’s foot, Ringworm, Valley fever, sore throat, influenza, rheumatism, tuberculosis, etc.
As Industrial Tools
Fungi play a vital role in some core industries of common life, discussed as under:
In Medicinal Industry
Some life-saving antibiotics are prepared from fungi i.e. Penicillium, Aureomycin, Streptomycin, Terramycin\ and many other medicines are prepared from various species of fungi. Similarly, predatory fungi of microscopic worms and growth regulator (Gibberellin) are also used.
In Useable Producing Industries
The fungus has also been used for baking, preparing alcohols, Ergots, alkaloids, Cheeses etc. in the fermentation and other chemical processes (Yeast/Saccharomyces).
Soil Fertilizing Agents
Saprophytic, parasitic, facultative Saprobic and mutualistic mode of nutrition of fungi is an important tool for recycling of nutrients/release of nutrients which increase soil fertility because of chemical structural changes in soil’s composition.
Fungi have apical and fast growth. It has a short lifespan and occupies less space. All things make the fungi almost immortal.
Some species of mushrooms are edible. These species are used as delicious food by well to do a class of human beings.
Structure of Fungi
Like all other living, organisms cell is the basic unit of structure and function of plant body structure. The cell of Fungus may be of Prokaryotic or Eukaryotic type.
There are more than 3000 terms used to describe the structure of fungi. However, a few are mentioned here to describe the structure of fungi along with a discussion of the organization of the fungal plant body. The cell of fungi has a definite cell wall and other cellular organelles but devoid of the chloroplast.
It is unicellular or multicellular, microscopic threads like structure which have two types:
i). Coenocytic or Non-Septate: – Without cross walls, cytoplasm move freely.
ii). Septate: – Hyphae having cross walls.
Hyphae are colourless at an early stage and are hollow and cylindrical. On the basis of a number of nuclei they are: –
a). Multinucleate. When Coenocytic hyphae usually contain more than one nucleus.
b). Uninucleate. Where one cell of septate hyphae contain one nucleus.
Mycelium is a group of hyphae forming the cobwebby structure of hyphae usually somatic cells. Mycelium is considered an assimilative part of the fungal body.
The plant body of fungi is called Thallus. Thallus may be unicellular (if consisting of one cell) or multicellular containing many cells. Part of Thallus may be called Thallus.
The thallus is also called soma or assimilative body of a fungus. A thallus is a unit of function of fungi performing all normal functions i.e. Reproduction, Growth etc.
Vegetative Structure of Fungi
Fungi form many types of vegetative structures. Some of them are as follows:
Mycelial Felt or Plate
Fungi species like Fomes pinicola and Tramets cubensis produce fan-like structure which is an aggregation of hyphae on the surface or inside or an organic matter. Hyphae are not distinguishable. The felt or plate is of brown colour rot.
It is also a group of hyphae forming Pseudo tissue. It is of two types:
i). Prosenchyma: – It is an aggregation of hyphae in such a pattern that each hypha are identifiable/recognizable.
ii). Pseudoparenchyma: – In this type of Plectenchyma fusion of hyphae takes place so that hyphae are not recognizable. It appears to be true parenchyma. It is a network of three types of hyphae.
a). Generative Hyphae: – Present in fruit body and carry out reproduction.
b). Skeletal Hyphae: – Thickly walled non-Septate, branched or unbranched structural/supporting function.
c). Binding Hyphae: – Thin-walled, much-branched having binding/glueing function.
If only generative hyphae are present such system is called monomitic, if generative and skeletal are present it is dimitic system and if generative, skeletal and binding hyphae are present it is called trimitic hyphae system.
A sclerotium is hard to structure formed by hyphae under unfavourable condition. Hard structure surrounds food-depositing hyphae called medullae and surrounding hard structure called rind. Under favourable climatic conditions, the rind breaks releases medullae which grow to fructification.
Sclerotium may be on surface, partly or more immensed on surface of host wood. Species forming Sclerotium are Claviceps purpura, Rhytisma Spp, Rhizoctina Spp.
iv). Rhizomorphs: – In some species of fungi i.e. Rhizopus, Rhizopydium, Chrytridiomycetes produce Rhizoids by aggregation of hyphae. Rhizoids are a chord, string like, and finger-like structure capable of apical growth. Rhizoids have same function as roots but different anatomy.
Rhizomorph has an outer rind and inner medulla as in Armillaria mellea.
NUTRITION IN FUNGI
As fungi lack chlorophyll, therefore, it is heterotrophic because it cannot synthesize food itself. It is, however, interesting that digestion of food material takes place outside the body and is taken in after that parasitically or saprophytically or by mutual sharing.
In some cases, fungi can synthesize vitamins and proteins presence of elaborated carbohydrates, sucrose, or glucose. Fungi can be divided into four groups on the basis of mode of nutrition.
- Parasitic mode of nutrition.
- Saprophytic mode of nutrition.
- Facultative Parasitic or Saprobic mode of nutrition.
- Mutual Sharing mode of nutrition.
- Parasitic Mode of Nutrition: – It is a mode of nutrition in which host/substratum is living thing. Fungi get its food material by residing on surface or inside the host. Epiparasitic mode if resides on surface and enoparasitic if resides inside the body of host. However, in both cases it does not want to kill the host.
When fungi resides inside the host it will have absorption of food material in two ways:
a). When fungi is present between the cells, its cell wall indirect contacts with cells of host sends absorbing organs called “Haustoria” into cells. This type of absorption is called “Intercellular”.
b). When fungi grow within the cells of the host no absorbing organs are needed. It absorbs food directly by diffusion, Osmosis process. This type of absorption of food is called “Intracellular”.
Fungi which cannot live without living host is called “Obligate parasite”.
- Saprophytic Mode of Nutrition: – In this mode of nutrition host is dead body of living organism or dead organic matter. Extracellular enzyme activity of fungi digests the food which is absorbed by the fungi.
The class of fungi is incapable of infecting the living organisms is called ”Obligate saprophyte”.
- Facultative Mode of Nutrition: – This mode of nutrition of fungi is further sub-divided into two groups:
i). Facultative Parasitic Mode: – In this case, fungi absorb its food from living host and cause the disease to it.
ii). Facultative Saprobic Mode: – In this case fungi produce disease-causing agents on the dead organic matter and it acquires its food from dead organic matter.
- Mutual Sharing Mode of Nutrition: – It is the mode of nutrition in which fungi and host both have a symbiotic relationship with each other as both are beneficial for each other. The example of symbiotic/mutual sharing is “Micrhizae”. Mycorrhizae are an association of fungi and roots of higher plants.
Fungi reside over roots of higher plants. Fungi get food from roots of plants. Roots of plants in such an association are always without root hair. Thus these plants are deficient in absorbing water and other nutrients from the soil. This job is carried by the fungi. Thus host and guest both grow normally.
GROWTH IN FUNGI
Growth is a phenomenon associated with life. It is a gradual increase in the size of the body due to increase in the number of cells through mitotic cell division. Certain factors affect the growth of plant body/Thalus of fungi. Fungi being deficient in chlorophyll always are dependent upon host called substratum for nutrients and growth. The growth rate of fungi on substratum depends upon:
- Temperature: – Temperature is an important climatic factor directly affecting the growth rate of fungi. Therefore, it can classify the rate of growth. The temperature in which fungi can grow is from below 0 C to 100 C. The normal range of temperature for growth is 0 C to 35 C. Most species of fungi grow within this range. 20 C to 30 C is an optimum temperature where the growth rate of most fungal species is maximum. The optimum temperature is a condition where all processes regarding are performed at a handsome rate.
- PH of the Substratum/Medium: – PH is antilogarithm of H+ or OH- concentration in the substratum. Its value ranges from 0-7 (Acidic), 7 neutral and 7-14 (Basic). Fungi grow normally at PH value 6.0, which is slightly acidic. However, it can grow above and below this value.
- Humidity: – it is the amount of water in the air usually taken in %age values. Fungi can grow in an atmosphere having humidity below 15% and up to 80%. 15% to 25% is a range where fungi can grow normally. The optimum level of humidity is 20% where growth rate is maximum.
REPRODUCTION IN FUNGI
Every living specie has tendency to maintain/retain its generation. To fulfill this tendency they have acquired a process of reproduction/continuity of generation. Reproduction may be defined as under:
“Process of reproducing of new individual having the characteristic feature of its parent”.
Before coming to methods of reproduction in fungi we come to some terms regarding reproduction.
- Eucarpic Fungi: – Such species of fungi in which a thalus of fungi have both generative as well as somatic parts.
- Holocarpic Fungi: – Such species of fungi in which all the thalus act as generative part. It may further be divided into two types:
- Hermaphrodite: – Having both male and female sex organs on the same thallus. It may also be called monoecious.
- Dioecious: – Having male and female sex organs on the different thali.
There are two types of reproduction in Fungi.
It is a mode of reproduction in which there is no fusion of sex cells (gametes). In this type of reproduction large number of individuals can be produced in a single season under favorable conditions. Asexual cycle can be completed many times in a single season.
There are different methods of asexual reproduction in fungi.
- Fragmentation: – It is the mode of reproduction asexually in which hyphae breaks up into cells. Each cell develops into hyphae. This fragment or a cell is generally called oidia. Fragmentation may occur by decision or by accident.
- Fission: – In this mode of reproduction a cell splits into two cells and cell wall is developed to break cell into two cell. Each daughter cell has divided nucleus and cytoplasm. This mode is common in yeast.
- Budding: – It is the mode of reproduction in which an outgrowth is produced on parent cell. This outgrowth is called bud. It may be single in number or there may be a chain of such buds. Each bud has cytoplasm and nucleus. Cell wall restriction departs him from the parent cell. Budding is a common asexually reproduction method in yeasts.
- Spore Formation: – Spore formation is a common method of reproduction in fungi. Spores are produced in sporangium which is then sporangiophore. The spore may vary in :
- Color: green, yellow, orange, red, brown or black.
- Size: a minute to large.
- Shape: globose, oval, oblong, needle-shaped, helical.
- Number: from one to many.
The arrangement of cells.
There are four different types of spores produced in fungi asexually:
i). Oidia: – These are spores produced at apical points by pinch off singally by fragmentation. These spores are thinly walled.
ii). Conidia: – These are spores produced in the chain at the tips of spore-producing hyphae or sporangia. These are also thinly walled.
iii). Arthrospores: – These are spores like Oidia and are also thinly walled.
iv). Chlamydospores: – These are spores produced under unfavorable conditions. These are produced at various/any place in the thalus and develop a thick wall around sporangium.
In lower fungi spores are usually motile. The motile spores are called Zoospores. Sessile spores are called aplanospores.
The moving spores have flagella. Flagella are locomotory organs of spores. They are two types of flagella i.e. Whiplash and Tinsel.
Whiplash has a basal portion such rigid and longer than Tinsel.
Whatsoever the mode of reproduction is asexually it is a mitotic division which carries out the process.
It is a combination of two compatible nuclei of fungal Thalus forming structure called gametangia. Gametangia give rise to new Thalus of fungi.
There are three phases in the process of reproduction in fungi sexually:
i). Plasmogamy: – It is the first phase in which two different cells come close together and union of cytoplasm takes place.
ii). Karyogamy: – It is the second phase of sexual reproduction. In this phase, the two nuclei (compatible) unite which were brought closer by Plasmogamy.
In higher fungi, Karyogamy does not take place just after plasmogamy. Thus a combined cell contains two nuclei for some or more time. This all having two nuclei is called dikaryon.
Karyogamy produces diploid (2n) zygote.
iii). Meosis: – Zygote produced by karyogamy having a diploid number of chromosomes. Meiosis takes place in zygote producing four haploid nuclei.
These three processes are called phases of the sexual cycle of fungi. These processes occur in a regular sequence and usually at specific points.
- Gametangia: – These are sex organs of fungi.
- Gametes of Fungi: – Gametes or sex cells are produced in gametangia.
- Isogametes: – Having similar shape and size of both the gametes.
- Anisogametes: – These gametes are morphologically similar but size is different.
- Heterogametes: – Male and female gametes have different sizes. Male is small and motile while the female is large and generally sessile. Male gamete is called anthridium/anthoridia and female gamete is called oogonium/oogonia.
Fusion of Gametes in Fungi: –
There are four different methods of fusion/union of gametes to form zygote in fungi:
i). Planogametangial Coupulation: – It is the fusion of two motile gametes called planogametes and these male and female gametes are naked. Lower fungi have isogamous planogametes in which gamete are similar in shape and size. Anisogamous planogametes have the same shape but different size. Heterogamous planogametes have different male (antheridia) and female (oogonia) gametes.
The male gamete enters into the female gamete and fuse to form zygote.
ii). Gametangial Contact: – In this method of fusion of nuclei, protoplasm of one gamete is transferred to other gametes through fertilization tube when two gametes of opposite sex come in contact with each other. Fertilization tube serves as passage of male nuclei and anthridium disintegrates.
iii). Gametangial Coupulation: – In this type of fusion of two gametangia come in contact and fusion of male and female gametes takes place in two ways:
a). A hole/pore develops between two gametangia. Nuclei from male gametangia to female gametangia takes place.
b). Fusion of walls of two gametangia at the point/area of contact and fusion of two gametangia into one takes place.
iv). Spermatization: – In this method many, small sized, Uninucleate sperm like male gametes are produced in structure called spermatium. Insects, wind or water takes these male gametes to female gametangia or even to somatic cells of thalus. Pore develops at the point of contact and receiving cell acts as female gamete.
v). Somatogamy: – No sex organs are developed by some species of higher fungi. In these species somatic cells fuse to form zygote.
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