Kingdom Fungi Overview:
The Kingdom Fungi includes eukaryotic, generally multicellular organisms with an unusual form of multicellularity. Their cells are not entirely divided by cell walls, so cytoplasm and even nuclei can flow between individual cells. The cell walls are made of chitin, a protein also found in the exoskeletons of arthropods, which reflects the close relationship between the Fungi and Animalia kingdoms. They are more closely related to each other than they are to plants.
Fungi are split between acting as parasites, which prey on insects, plants, and animals, and saprophytes, which primarily aid in the breakdown of dead organic material. Fungi can also live in symbiotic relationships with other organisms. Lichens are the result of a symbiotic relationship between a fungus and a photosynthesizing organism. Other fungi live in symbiosis with plant roots to increase the root surface area.
Fungi can be divided into three groups based on relatedness and shared reproductive habits: Basidiomycota, Ascomycota, and Zygomycota. Basidiomycota are characterized by the presence of basidia and dikaryotic fruiting bodies and include the mushrooms, puffballs, and shelf fungi. Ascomycota are characterized by the presence of asci and include such diverse organisms as the cup fungi and mildews as well as the unicellular fungi, yeast. Zygomycota are characterized by the presence of a thick-coated zygospore and include bread and other molds, plant and animal parasites, as well as many plant-root symbionts.
The complete multicellular body of fungus is called MYCELIUM, which is composed of white fluffy mass of branched hyphae.
A few of true fungi are unicellular (such as yeast) but most have multicellular body (mycelium) consisting of long, slender, branched, tubular, thread like filaments called as Hyphae which spread extensively over the surface of substrate.
Types of Hyphae:
Hyphae can be divided in to two types:
- Septate or Multicellular Hyphae
Those hyphae which are separated by cross-walls called “septa” into individual cells containing one or more nuclei , are called “Septate Hyphae”. For example Mushrooms.
- Non-septate or multinuclear or coenocytic hyphae.
Those hyphae, which lack septa & are not divided into individual cells, instead these are in the form of long, multinucleated large cells are called Non-septate or Coenocytic Hyphae.For example Mucor & Rhizopus
Cell Wall of Hyphae:
Chittin is the chief component present in the cell wall of most fungi, because it is more resistant to decay than are the Cellulose & lignin which make up plant cell wall.
Cytoplasm of Hyphae:
In septate hyphae, cytoplasm flows through the pores of septa from cell to cell, carrying the materials to growing tips & enabling the hyphae to grow rapidly, under favorable conditions.
In non-septate hyphae, cytoplasm moves effectively, distributing the materials throughout.
Nuclei of Hyphae:
All fungal nuclei are HAPLOID except for transient diploid zygote that forms during sexual reproduction.
Main Function of Hyphae:
Extensive spreading system of Hyphae provides enormous surface area for absorption.
Nutrition in Fungi:
All fungi lack chlorophyll & are heterotrophs ( obtain carbon & energy from organic matter, They obtain their food by direct absorption from immediate environment & are thus “Absorptive Heterotrophs”.
Different Modes of Heterotrophic Nutrition in Fungi:
Being Heterotrophic, fungi can exist as
- Saprotrophs or saprobes (Decomposers)
Saprobic fungi along with bacteria, are the major decomposers of biosphere, contributing to the recycling of the elements (C,N,P,O,H & etc.) used by living things. Those fungi which obtain their food (energy, carbon & nitrogen), directly by digesting the dead organic matter are called “SAPROBIC Fungi” or “DECOMPOSERS”
Those fungi which absorb nutrients directly from living host cytoplasm are called Parasitic Fungi.
Types or Parasitic Fungi
Parasitic fungi may be of two types
- Obligate parasites
Those parasitic fungi which can grow only in their living host & cannot be grown on available defined growth culture medium, are called “ Obligate Parasites”. For example Many mildews, Most of Rust species.
- Facultative parasites
Those parasitic fungi which can grow parasitically on their host as well as by themselves on artificial growth media, are called “ Facultative Parasites”.
- Obligate parasites
Those fungi which obtain their food by killing other living organisms are called Predatory Fungi. For Example
- Oyster Mushrooms (Pleurotus astreatus).Oyster mushroom is a carnivorous fungus. It Paralyses the nematodes (that feed on this fungus), penetrate them & absorb their nutritional contents, primarily to fulfill nitrogen requirements. It fulfill it glucose requirements by breaking the woods.
- Some species of Arthrobotrys.
Constrictor ring development Some species of Arthrobotrys trap soil nemotodes by forming CONSTRICTING RING, their hyphae invading & digesting the unlucky victim.
Those fungi which form such symbiotic associations with other living organisms in which both partners of association get benefit from each other are called Mutualistic Fungi & Such association are called as “Mutualistic Symbiotic Association”.
Two Mutualistic Symbiotic Associations formed by Fungi:
Fungi form two key mutualistic symbiotic associations. These are
Symbiotic Partners in Lichens
Lichens are mutualistic & have symbiotic associations b/w certain fungi (mostly Ascomycetes) & imperfect fungi & few Basidiomycetes (about 20 out of 15000 species of lichens) & certain photoautotroph either green algae or cynobacterium or sometimes both.
In lichens, fungi protect the algal partner from strong light & desiccation & itself gets food through the courtesy of alga.
Areas where Lichens Grow
Lichens can grow at such places such as bare rocks & etc, where neither of the components alone can grow.
Ecological Importance of Lichens
From ecological point of view, lichens are very important because they serve as Bio Indicators of Air Pollution
Mycorrhizae are mutualistic association b/w certain fungi & roots of vascular plants (about 95% of all kinds of vascular plants).
The fungal hyphae dramatically increase the amount of soil contact & total surface area for absorption & help in direct absorption of nutrients from soil. The plant on the other hand, supplies organic carbon to fungal hyphae.
Types of Mycorrhizae
There are two main types of mycorrhizae.
In Endomycorrhizae, the fungal hyphae penetrate the outer cells of plant root, forming coils, swellings & minute branches, & also extend out into surrounding soil.
In Ectomycorshizae the hyphae surround & extend between the cell but don’t penetrate the cell walls of roots. For example Mutualistic association between fungi & pines & firs.
Classification of Fungi:
There are four major divisions of fungi, which are divided on the basis of their sexual reproduction.
Zygomycota are by far the smallest of four groups of fungi, with only about 600 named species. This group includes more frequently bread molds as well as a variety of other microscopic fungi found on decaying organic material.
The group is named after a characteristic feature of the life cycle of its member,the production of temporalily dormant structures called Zygopors.The zygomycetes lack septa in their hyphae i.e coenocytic hyphae, except when they form sporangia or gametangia.
The second division of fungi, the Ascomycota is a very large group of about 30,000 named species with many more being discovered each year.
The ascomycota are named for their characteristic reproductive structure, the microscopic, club shaped ASCUS.
Type of Hyphae:
The hyphae of ascomycetes are divided by septa i.e septate hyphae, but the septa are perforated & the cytoplasm flows along the length of each hyphae. The septa that cut off the asci & conidia are initially perforated like all other septa, but later they often become blocked.
Life Cycle of Ascomycota:
In life cycle of ascomycota, Both sexual & asexual reproduction occurs.
Sexual Reproduction in Ascomycota:
Sexual reproduction occurs through following steps.
- Formation of Male Gametangium or Antheridium
The hyphae of ascomycetes may be either homokaryotic & heterokaryotic. The cells of these hyphae usually contain from several to many nuclei. These cells form Antheridium or male gametangium.
- Female Gametangium or Ascogonium
The gametangium which develop beak like out growth called as TRICHOGYNE, is called female gametangium or Ascogonium.
- Fusion Male and Female Gametangium
When antheridium is formed , it fuses with trichogyne of an adjacent ascogonium.Fusion of cytoplasm or plasmogamy occurs.
- Pairing of Nuclei:
After plasmogamy, nuclei from antheridium then migrate through the trichogyne into the ascogonium, & pair with nuclei of opposite mating types.
- Formation of Dikaryotic Hyphae & Dikaryoticy:
Dikarytic hyphae then arise from the area of fusion. Throughout such hyphae,nuclei that represent the two different original mating types occur ( Dikaryoticy) Such hyphae are also called as Heterokaryotic Hyphae.
- Formation of Ascocarps or FRUITING BODIES:
Excessive growth of monokaryotic or dikaryotic hyphae results in formation of massive structures of tightly interwoven hyphae, called as FRUITING BODIES of Ascocarps, which corresponds to the visible portions of a morel or cup fungus.
- Asci Formation:
Asci are special reproductive structures which are formed on special fertile layers of dikaryotic hyphae with in the Ascocarps.
- Separation of Asci:
The Asci are cut off by the formation of septa at the tips of heterokaryotic hyphens.
There are two haploid nuclei with in each ascus one of each of which belongs to different mating type. Fusion of these two nuclei occurs within each ascus called as SYNGAMY.
- Zygot Formation:
Syngamy results in zygote formation, which divides immediately by meiosis,forming four haploid daughter cells.
- Formation of ASCOSPORES:
Four haploid daughter nuclei, usually divide again by mitosis , producing 8 haploid nuclei that become walled & called ASCOSPORES.
- BURSTING of ASCUS:
In most Ascomycetes, the ascus becomes highly turgid at maturity and ultimately
bursts, often at a perforated area, which may be pore or slit or lid
- DESPERSION & GERMINATION of ASCOSPORES:
After bursting, the ascospores may be thrown as far as 30 cm. Under favorable
circumstances they germinate giving new hyphae.
Asexual Reproduction in Ascomycota (By Condia Formation)
The type of asexual reproduction in fungi in which large number of asexual spores called Conidia are formed, each on germination giving rise to new mycelium is known as Conidial Reproduction.
Conidia are non-motile, asexual spores which may be produced in very large number & can survive for weeks, causing rapid colonization on new food.
Conidia are not developed inside the sporangium but they are usually cut off at the end of modified hyphae called CONIDIOPHORES, commonly in chains or clusters. For example Asexual reproduction by conidia formation is very common in Ascomycetes.
Types of Ascocarps in Ascomycetes
According to their shape, Ascocarps are of following three types:
The ascocarps of cup fungi & the morels are open, with the asci lining the open cups called Opothecium.
Some ascocarps are closed & called as Clestothecium
Some ascocarps have small opening at the apex called as Perithecium. Ascocarps of Neurospora are of this type.
- Formation of Male Gametangium or Antheridium
The basidiomycetes, third division of fungi have about 16,000 named species.
More is known about some members of this group than about any other fungi.
Basidiomycetes are named for their characteristic sexual reproductive structures,
the Basidium, which is club shaped like as ascus.
Life Cycle of Basidiomycota:
In life cycle of Basidiomycota, reproduction is usually sexual. Asexual reproduction is not very important.
Sexual Reproduction in Basidiomycota:
The life cycle of basidiomycetes begin with the production of hyphae which may be of two types.
- Homokaryotic hyphae giving rise to primary mycelium.
Homokaryotic or monokaryotic hyphae lack septa at first. Eventually, However, septa are formed between nuclei of these hyphae. A basidiomycete myceliummade up of monokaryotic hyphae is called PRIMARY MYCELIUM.
- Heterokaryotic hyphae giving rise to secondary mycelium.
Mycelium of basidiomycetes, with two nuclei, representing the two differentmating types b/w each pair of septa, is called Secondary or Dikaryotic Mycelium. Most of the mycelium of basidiomycetes that occur in nature is dikaryotic & often only dikaryotic mycelium is able to form basidiocarps.
Formation of Basidiocarp or Fruiting Body
Dikaryotic mycelium is responsible for the formation of FRUITING BODY in Basidiomycetes called as Basidiocarp, made up of tightly interwoven dikaryotic hyphae.
Formation of Basium
Basidium is characteristic reproductive structure of Basidiomycetes, which is club shaped & formed with in the Basidiocarp. This produces slender projection at the end called as Sterigmata, in this way.
Sygnamy and Zygot Formation
Nuclear fusion or syangamy occurs in Basidium, giving rise to diploid zygote, the only diploid cell of the life cycle.
Maiosis and Besidiospore Formation
Meiosis occurs immediately after the formation of zygot, resulting in the formation of four haploid nuclei, which are incorporated in Basidiospores. In most member of this division basidiospores are borne at the sterignata
Dispersion and Germination
Same as in Ascomycetes
Asexual Reproduction in Basidiomycota:
In contrast to their effective sexual reproduction, asexual reproduction is rare in
Examples of Basidiomycetes Mushroom, Toad stools, Puff Balls, Jelly Fungi, Shelf Fungi Plant pathogens caleed Rusts and Smuts.
The fungi that are classified is this group, are simply those in which the sexual
reproductive stages have not been observed. In other words, most of the Fungi Imperfecti are as ascomycota that have lost the ability to reproduce sexually.
There are some 17000 described species of this group.
Sexual reproduction is absent among Fungi Imperfecti
Life Cycle of DEUTEROMYCOTA:
Although in life cycle of deuteromycetes or Fungi Imperfecti, true sexual
reproduction is absent, but there is certain type of Genetic Recombination which seems to be responsible for some of the production of new pathogenic strains of wheat rust.
Genetic Recombination in Fungi Imperfecti Parasexuality
In parasexuality, exchange of portions of chromosomes between the genetically distinct nuclei with in a common hyphae takes place. This is the special type of genetic recombination occurs in fungi Imperfecti.
Examples of Fungi Imperfecti
Among the economically important genera of Fungi Imperfecti are
- Most of the fungi that cause skin diseases in humans, including athlete’s foot and ring worm are also fungi imperfecti.
Economic Importance of Fungi
Fungi play a vast role in economic field they show both useful and harmful activities to human beings.
Following are some of the beneficial effects of fungi.
Many kinds of edible fungi are in the form of mushrooms, are a source of nourishing & delicious food dishes. But not all the mushrooms are edible. Some of them are poisonous and called as toad stools or death stool. Yeast, another kind of fungi, are utilized in baking industry.
Nearly two dozens antibiotics have been isolated from different types of fungi and bacteria, like Penicilliun from penecillium notatum, Neomycin, Chloromycetin, Tetramycin and etc.
Many kinds of Yeast are used in the production of bakery & brewery products. Some species of genus PENICILLIUM give characteristic flavors & aromas to the cheese.
Species of Aspergillus, are used for fermenting soya sauce & soya paste. Citric Acid is produced commercially with members of this genus under highly acidic condition.
Fungi maintain the soil fertility by decomposing the dead organic matter. For example Mycorhizal fungi.
Production of Organic Compounds
May species of fungi are used in the production of organic compound such as vitamins, proteins & fats. Saccharomyces, synthesizes a range of vitamin B group.
Following are some of the harmful effects of fungi,
Saprophytic fungi cause tremendous amounts of spoilage of food stuff. 15-20% of worlds fruit is lost each year due to fungal attack.
Spoilage of Wood and Leather Articles
Many fungi spoil leather goods, woods, wool, books, timber, cotton & etc. WOOD-ROTTING Fungi destroy not only living trees but also structural timber.BRACKET/SHELF Fungi cause lot of damage to store cut lumber as well as stands of timber of living trees.
Many fungi are poisonous . AMANITA VERNA is a mushroom, which produces deadly poisonous substance known as AMANITIN, which causes serious problems in respiratory system & blood circulatory system.
Some fungi during decomposing food release certain poisonous substances collectively known as Mycotoxins. Mycotoxins are the major source of food poisoning.
Fungi cause a number of diseases in plants as well as in human beings.
Plant Diseases by Fungi
Fungi destroy many agricultural crops, fruits, ornamentals & other kinds of plants because they produce several enzymes that can breakdown cellulose, Lignin and even cutin. Following are some of the serious plant disease caused by Fungi.
Rust and Smut Disease
Rust & smut diseases are serious diseases of WHEAT, RICE, CORN &other cerial crops. They cause extensive damage.
A serious disease of potato caused by a fungus known as Phytopthora Infestans. Other plant disease are
- Powdery mildews ( on grapes, rose, wheat & etc).
- Ergot of rye
- Red rot of sugar cane
- Potato will
- Cotton root rot
- Apple scab
- Brown rot of peaches, plums, apricots & cherries.
Animal Diseases Caused By Fungi:
Following are some of the fungal diseases in man.
Ring Worm and Athlete’s FOOT are superficial fungal infection caused by certain Fungi Imperfecti
CANIDIA ALBICANS, a yeast causes oral & Vaginal thrush.
Aspergillosis is the disease of ear & lungs caused by Aspergillius. It occurs only in person with defective immune system such as AIDS & cause death.
Some strains of ASPERGILLUS FLAVUS produce one of the most carcinogenic (cancer causing ) mycotoxins called AFLATOXINS.
Ergotism is caused by eating bread made from PUROLE ERGOT- Contaminated flour. The poisonous material in the ergot causes nervous spasm, convulsions, psychotic delusion & even gangrene.
Histoplasmosis is a serious disease of lungs caused by inhaling spores of a fungus, which is common in soil contaminated with bird’s feces.