Saccharomyces (Yeast)

Saccharomyces cerevisiae

Commonly employed in bread making and beer brewing.
Hence popularly called the brewer’s or baker’s yeast

Thallus 
Thallus is non-mycelial
It is not made up of hyphae
Consists of a single minute oval or spherical cell.
In some species yeast cell is elongated, cylindrical or rectangular in shape.
In size ranges from 2 to 8µ in diameterby 3 to 15µ in length.
Individual the yeast cell appears hyaline in colour.

Cell structure
The cell wall is thin, delicate, frim.
It is made up to two polysaccharides, namely, glucans and mannanB in combination with traces of protein, lipid and chitin.
There is no cellulose.
The cytoplasm is differentiated into two portions, the outer and the inner.
The outer portion is a thin cytoplasmic membrane (ectoplasm).
The inner portion is dense or granular. It is endoplasm
The endoplasm contains a single, small dense nucleus.
Occupying much of the space in the yeast cell is a single large vacuole.
The vacuole contains a solution called volutin.
Volutin is a complex material consisting of RNA, lipoprotein and poly-phosphates.
The reserve food product are in form granules of glycogen, oil globules.

Nutrition
They are saprophytes.
Obtains nutrition in form of simple sugars in solution.
It gets it from bruised ripe fruits, fruit juices, sugar solutions or crushed moistened grains.
The yeast cells secrete enzymes called the zymase.
The zymase changes the starch or complex sugars into simple sugars.
The latter diffuse into the endoplasm through thin, delicate cell membrane.
A small percentage of the absorbed sugar is used as food and assimilated.
When growing in a well aerated medium the rest of the sugar is completely oxidized into carbodioxied and water.
In absence or poor supply of oxygen the major portion of sugar is converted into carbondioxide and ethyl alcohol.
This is called alcoholic fermentation.
The products of this reaction (carbondioxide and ethyl alcohol) diffuse out into the surrounding liquid.
This process is utilized in the production of industrial alcohol, in wine making, in brewing and in bread making.

Reproduction
Vegetative reproduction

Budding
Under favourable conditions yeast exclusively reproduce by this method.
A small portion of cell wall, at or near one pole softens and thins.
The protoplast in this region, covered by the thin softened membrane, bulges out in the form of an outgrowth or protuberance.
The protuberance gradually increases in size.
It is known as the bud.
As the bud is forming, the nucleus of the parent yeast cell divides .
One of these daughter nuclei migrates into the enlarging bud.
The bud grows and becomes constricted at the base.
A double cross wall form and the two cells separate leaving a scar on the both cells.
The detached bud grows and starts budding again.
A new bud arises on the surface of the parent cell at the opposite end to the first and not from the same area.
This is know as bipolar budding.
In presence of abundant food the process of budding is quickened.
It becomes so rapid that the buds often produce new buds before separation from the mother cell.
This process is repeated.
This results in the formation of branced or unbranced chains of cell constituting the pseudomycelium.
Soon the chain breaks and cells are separated from each other.

Fission
Vegetative reproduction by fission has also been reported but it occurs in some other yeasts and not in Saccharomyces. 
They are called the fission yeasts.
The mother cell elongates. 
The nucleus divides into two.
The daughter nuclei move apart.
Meanwhile a ring-like ingrowth appears at the wall of the yeast cell in the middle.
It grows inward toward the centre of the cell.
Finally it stretches across the cell forming a complete partition called the septum.
The septum thickens and then splits into two layers, one for each daughter cell before they separate.

Sexual reproduction
No sex organs are produced.
Sexual process is extremely simplified.
It consists of three phenomenoa characteristic of the sexual process, namely plasmogamy, karyogamy and meiosis.
Haplo-Diplobiontic life cycle.
In a culture of brewer’s yeast there occur intermixed two kinds of somatic cells, namely, small dwarf strain and large strain cells.
Dwarf strain cells are small haploid cells.
Under normal conditions these multilply by budding and increase in number.
When food supply is scarce they enter a dormant phase and become resistant.
Under normal conditions and presence of the small haploid cells of opposite mating strain they function as gametangia and resort to gametangial conjugation.

Gametangial conjugation
During conjugation process the + and – strain of haploid dwarf cells agglutinize and form clusters.
The two haploid cells of the opposite mating types bend towards each other and fuse to form a conjugation bridge.
Plasmogamy
The fusion between the protoplasts of the + and – strain takes place through the conjugation bridge. 
It is called plasmogamy and a dikaryon is formed.

Karyogamy
The two nuclei of the dikaryon finally fuse. 
The diploid nucleus is called the synkaryon and the cell containing it is the zygote.

Zygote
The zygote formed is in fact the large strain yeast cells.
They are diploid, larger in size.
Under favourable conditions they multiply by budding and increase there number.
During unfavourable conditions, the diploid large strain yeast cells (Zygotes) resort to ascospore formation.
They become spherical in shape and directly function as asci
Ascospore formation
The ascus mother cell is spherical in shape.
Diploid nucleus of the ascus mother cell undergoes meiosis and forms four haploid nuclei.
An envelope encloses each of the four nuclei together with some cytoplasm and form 4 globose ascospores.
Two of these are of + strain and two – strain.
On the onset of favourable conditions, the ascospores are released due to rupture of ascus wall.
The mature ascospore is a thick-walled, globose structure.
The ascospore wall is differentiated into 3 layers.
Ascospore germinates and form a new mycelium.
In this both haplophase and the diplophase are of equal importance.
Hence it is called as Haplo-diplobiontic life cycle.

Diplobiontic life cycle
Diploid vegetative cell directly functions as ascus mother cell.
In this the diploid nucleus undergoes meiosis and form 4 haploid nuclei.
These four haploid nuclei transforms into 4 ascospores.
Two of these of + strain and two are of - strain
Ascospores are not released from the ascus.
Sexual fusion take place within the ascus between the ascospores of opposite strain.
Consequently two diploid zygotes are produced.
Each zygote germinates in situ to form a small germ tube.
The germ tube grows and emerges through the ascal wall and functions as a sprout mycelium.
The cells of the sprout mycelium budd off diploid cells.
Soon the diploid sprout cells get severed from the parent cells.  
These diploid sprout cells functions as acus mother cells.
In this type, the haplophase (gametophyte) is extremely reduced and diplophase is prolong.
Hence, this type of life cycle is called diplobiontic life cycle.
Ex. S. ludwigii

Haplobiontic life cycle
In this the vegetative cells are elongated, uninucleate and haploid.
Each haploid somatic cell is a potential gametangiu.
At the time of sexual reproduction two somatic cells come to lie side by side.
A conjugation tube is formed between the two cells.
The nuclei of the two conjugating cells migrate into the conjugation tube and fuse.
The diploid nucleu or zygote functions directly as an ascus mother cell.
Its diploid nucleus immediately undergoes meiotic division followed by a mitotic division.
This results in formation of 8 eight haploid nuclei.
These 8 nuclei get transformed into 8 ascospores.
The ascus mother cell with eight ascospores is called an asucs.
The ascal wall ruptures and the ascospores are released.
The liberated ascospores on germination, enlarges and behaves like a somatic cells.
In this case the diplophase is very short.
It is represented only by a zygoe cell which undergoes meiosis immediately after karyogamy.                                                                 
The haplophase is long.
Hence this is called as Haplobiontic life cycle.
Ex. Schizosaccharomyces octosporus.

Actinomycetes

Actinomycetes

Gram positive, filamentous, aerobic, non motile bacteria.

Discovered by Bollinger in the lesions of lumpy jaw

(actinomycetes) in cattle.

The group has been placed separately in volume 4 of the Bergey’s Manual of Systematic Bacteriology.

The name of the group is derived from the genus name Actinomycetes meaning ‘ray-fungi’
(Gr. Action – rays, mykes- fungus)

They are basically soil inhabitants. They comprise 10 to 50% of

total microbial population in soil. However few types of actinomycetes are found in the body cavities

of man and animals.

On solid substratum, the branching network of hyphae developed by actinomycetes grow both on the s

of the substratum called aerial hyphae and inside the substratum called  substrate mycelium.

Septa usually divide the hyphae into long cells containing several nucleiods.

Many actinomycetes have aerial mycelium that extends above the substratum and form asexual, thin walled spores, conidia or conidiospores on the ends of filaments.

The mycelial structure and the formation of aerial branches and spores give these organisms the appearance of fungi

Most actinomycetes are non-motile, when motility is present it is confined to flagellated spores.

1. The cell wall composition of actinomycetes varies greatly among different groups.
2. Four major groups cell types can be distinguished according to three feature of peptidoglycan composition and structure i. the amino acid in tetrapeptide side chain postion, ii. The presence of glycine in interpeptide brides, and iii. Peptidoglycan sugar content.
3. Reproduction: Actinomycetes, like other bacteria, reproduce only asexually. The asexual mode of reproduction is accomplished by arthrospore or conidia or conidiospore.
4. Arthrospore formation: the filamentous bodies of the actinomycetes break into rod-shaped smaller fragments called arthrospores. Each is capable of growing into a new filament.
5. Conidia formation: Condia formation is a common method of reproduction in some members of actinomycetes. The filamentous branched actinomycetes produce smaller, oval or rounded structures called conidia terminally on certain apical branches called conidiophores. Each conidium germinates giving rise to a actinomycetes cell. Ex. Streptomyces.

Economic Importance

Producers of Antibiotics

More than 500 antibiotics have been obtained
from different species of streptomycetes

Example:

Streptomycin – Streptomyces griseus

Neomycin      - S. fradiae

Tetracycline  - S. aureofaciens

Erythromycin – S. erythreus

Clindamycin   - S. lineolnesis

            Chloramphenicol – S. venezuelae

In Agriculture:

As a agent of Biological control

There are innumerable reports of actinomycetes
with activity against plant pathogens or
reports concerning the prevelance of
antagonistic actinomycetes in the rhizosphere of
diseased plants.

It has been currently reported that addition ,
of cellulosic products (rice stubble or water
hyacinth biomass) results in the reduction of
cauliflower damping off by Rhizoctonia solani.
This reduction has been ascribed to the
stimulation of antagonistic actinomycetes.

Spores of Phytopthora have been shown to be
parasitized by species of Actinoplanes, Amulariella.
This phenomenon is called hyper parasitism.

As a enhancers of plant growth

Some free living actinomycetes have been shown to be
indirectly involved in production of Vitamin B in Pine
rhizosphere. Since mycorrhiza require these vitamins,
actinomycetes are indirectly involved in plant growth
enhancement.

As producers of agriculture chemicals

Actinomycetes are responsible for antibiotics
used in agriculture as agents of control of
bacterial and fungal diseases and insects pests.

Drugs having insecticidal value are Monensin,
salinomycin.

Nutritional antibiotics are given to farm animals
for better growth and assimilation of feed are
moenomycin and elfacins.

The antifungal antibiotics used in plant disease
control derived from streptomyces  include
cyclohexamide, blasticidin (against rice
blast pathogen), polyoxins (against Alternaria spp)

Mineralisation of organic matter

Actinomycetes can degrade enormous
number and variety of organic compounds
and are extremely important in the mineralization
of organic matter.

Harmful

As animal pathogen

Several members of actinomycetes are pathogens
of cattle and farm animals

Corynebacterium pyogenes causes mastitis,
pharyngitis and urethrites in sheep, cows, swine
and horses. Mycobacterium farcinogenes causes
subcutaneous inflammation of lymph nodes and
vessels in cattle.

As Human pathogen

They  are causative agents of a few human diseases  
such as actinomyosis, various abscesses.

T

I Semester Important Questions

I Unit

Short Questions
1. Heterocyst   2. Hormogones   3. Akinetes   4. Endospores    5. Actinomycetes    6. Archaebacteria

7. Bio fertilisers  8. Phycobiont and Mycobiont   9. Types of lichens

Long Questions

Brief account on Archaebacteria
General Characters, Cell Structure and thallus organisation in cyanobacteria
Structure and reproduction of Nostoc
Structure and reproduction of Anabaena
Structure and reproduction of Oscillatoria
Sexual Reproduction of Lichens
Internal Structure of Lichens
Special structures of Lichens

II Unit
Short Questions
1. Capsid and Capsomeres  2. types of viruses   3. Gram staining    4. Koch Postulates
5. Binary fission   6. Bacterial Flagella  7. Types of Bacteria depending on shape
8. control of viral diseases  9. TMV   10, Bacteriophage  11. Lytic and lysogenic phage  12. Prophage

Essay Questions
Structure of Bacterial cell and nutrition in Bacteria
Sexual Reproduction in Bacteria
Asexual Reproduction inBacteria
Reproduction or replication in Virus - Lytic and lysogenic phase
Economic importance of Bacteria - Useful and Harmful
Diseases caused by viruses and its prevention

Unit III
Short Questions
1. Algal Flagella  2. Pigments in Algae  3. Reserve Food In Algae  4. Gonidium  5. Globule and Nucule   6. Nandria   7. Gonidia  8. Plakea Stage   9. Algal Blooms   10, Bio Fouling  11. Cap cell
12. Coenobium  13. Asexual Reproduction in Volvox   14. stephanokontic zoospores  15. Amylum stars
Essay
General characters of Algae
Economic Importance of Algae
Thallus Structure in Algae
Reproduction in Oedogonium
Life Cycle of Volvox
Life Cycle of Chara
Life Cycle of Ectocarpus
Sexual Reproduction in Polysiphonia
POst fertilisation changes in polysiphonia and structure and importance of Cystocarp

Unite IV
1. Autoecious and Heteroecious rust  2. Micro and Macrocyclic rust   3. Mycorrhizae  4. Budding
5. Nutrition in Fungi  6. Importance of Penicillium


Essay
Asexual reproduction in Albugo
Sexual Reproduction in Albugo
LIfe cycle of Yeast
Sexual Reproduction in Penicillium
Rust on Wheat or primary host
Rust on Barberry or secondary host
Economic importance of fungi

Puccinia

                                                                Puccinia   

Diagrams are same as drawn in the Record

         

                                                                                                    Division : Eumycota

                                                                                                            Sub Division : Basidiomycotina

                                                                                                            Class : Teliomycetes

                                                                                                            Order : Uredinales

                                                                                                            Family : Pucciniaceae

                                                                                                            Genus : Puccinia

The species of Puccinia are obligate parasites on higher plants. They are popularly known as Rust fungi, because of characteristic reddish, brown colour of their spores. The genus includes about 700 species and of them about 147 species are recorded in India.

They are of great economic importance as they cause destructive rust diseases of major corps such as wheat, barley, sorghum, maize, bajra, groundnut, sunflower etc.

The rusts have a pleomorphic life cycle, having more than one independent form or spore – stage in the life cycle. Many rust have a complex life – cycle producing five different types of spores, produced at 5 reproductive stages. The spores are –

            Stage 0       : Spermogonia  ( Pycnidia) bearing spermatia ( Pycniospores) and receptive hypae

            Stage I        : Aecia bearing aeciospores

            Stage II      : Uredinia bearing Uredospores

            Stage III    : Telia bearing teleutospores

            Stage IV    : Promycelia bearing basidiospores

The rust fungi which produce all the five types of spores in their life cylcle are called as macrocyclic rusts. If one or two spore stages are missing in the life cycle, it is described as microcyclic rusts.

The species which complete their life cycle producing all the spores types on a single host  are called as autoecious speices, ex – P. Asparagi, P. helianthi. The species which complete their life cycle producing all the spores types on two different unrelated host plants, are called heteroecious, Ex – P. graminis

In the case of heteroecious rust, the host which bears uredial and telial stages (sexual or perfect stage) is called the primary host. The host which bears pycnidial and aecial stage is called the secondary host or alternate host.  Some autoecious rust produce the same type of spores on several unrelated host plants. These unrelated host plants are called collateral hosts.

Life Cycle of Puccinia graminis tritici

P. graminis tritici is the casual organism of the black rust disease of wheat. The fungus is polymorphic in nature, as it produces five types of spores during its life cycle. It is therefore also called macrocyclic rust. The life cycle is completed on two different host plants, hence called heteroecious rust.

The wheat plant on which the parasite passes its dikaryotic phase is called the primary host and the Barberry (Berberis vulgaris) is the secondary or alternate host. The fungus can survive in the absence of the alternate host, but it can produce new races by hybridization only on barberry.

Out of the five spore types in the life cycle, urediniospores and teliospores are produced on the wheat plant, whereas pycniospores and aeciospores are produced on the alternate host.

Life Cycle on Wheat

When aeciospores released from the infected barberry plants falls on the wheat leaves, they germinate under favourable conditions and germtubes enter the leaves through stomata. the mycelium is intercellular, septate and branched. The septal  pore is simple.

The mycelium is dikaryotic, each cell contains a pair of nuclei (n + n) constituting a dikaryon. To obtain the nutrition the intercellular hyphae develop intracellular food absorbing haustoria.

Reproduction

Within about 7 -21 days of infection, the dikaryotic mycelium reproduces by sporulation. The spores produced are of two kinds – the uredospores and teleutospores.

Urdineal Stage:

The dikaryotic mycelium begin to aggregate below the epidermis of the infected organ such as leaf, leaf sheath, stem. From the mycelium, many vertical hyphae called sporophores arise towards the epidermis. They are arranged in a close palisade –like layer. The tip of each hyphal stalk swells to form a single binucleate uredopsore or uredeniospore. The uredospores are thus formed in groups. Each group is called a uredosorus or uredinium.

Structure of Uredospore:

Each uredospore is a unicellular, dikaryotic, oval and brown structure. It has a thick, echinulate or spiny wall. The wall consists of two layers – outer thick spiny exospores having four germ pores, and an inner delicate, hyaline endospore. The uredospores contain cytoplasm, oil globules and brown pigment. In masses the uredospores appear rusty red colour.

The huge number of uredospores exert pressure on the epidermis which is, at first, lifted but finally ruptured in form of slits or blisters. They appear in form of reddish – brown patches on the stems and leaves and called as pustules. This stage is called the ‘Red Rust of Wheat’. As a result of this, the entire field crop appears to be burnt by fire (Gr. Urere = to burn).

The uredospores get detached from their stalks and are disseminated by wind.

Germination of Uredospores

On falling on another wheat plant and in the presence of moisture and optimum temperature ( 20 -25⁰ C)  the uredospore germinates within a few hours. The endosporium comes out in form of a slender tube through germ pore. More than one germ tubes may be produced by the same uredospore.

The germ tube by elongation grows over the surface of the host leaf till it reaches a stomata where its tip swells to form an appresorium. The two nuclei and the protoplasm of the germ tube migrate to the appresorium.

The peg – like outgrowth, the infection peg arises from the appresorium. It enters the stomatal aperature. Reaching the substomatal cavity the tip of the infection peg swells into a vesicle. The contents of appresorium pass through the infection peg into the vesicle. One or more hyphae develop from the vesicles, grow  into dikaryotic mycelim and ramify in the intercellular spaces.

This mycelium is again capable of producing urediniospores. These spores are thus ‘’ repeating spores” and they multiply and propagate the disease in the field as long as the weather is favourable. This repeated cycle recurs several times in a single growing season.

Telial Stage

Late in the growing season another kind of spore develops form the same dikaryotic mycelium. This spores are termed as teliospores or teleutospores. The pustules are called telia or teleutosours.

The teleutospores are developed among the uredospores in the same uredosorus. Gradually , as the season progresses more and more teleutospores are produced , whereas the number of uredospores is reduced. Finally, the sori conatin only the teleutospores. These sori are called the teleutosori. 

The cells of the mycelium producing the teleutospores are called the telia. The teleutospores are dark brown or black colour. The teleutospores exert pressure on the epidermis, which is ruptured and the telia appear as black raised streaks along the leaf sheaths and stems. Hence, this stage is called the black stem rust.

Structure of teliospore

The teleutospores are black or dark brown, stalked, two-celled, spindle shaped structures. The spore wall is thick and smooth. There is a single germ pore in the wall of each cell. It is at the apex in the upper cell and below the septum in the lower cell.

This stage in the life cycle, in which teliospores ( Gr. Telos = end) are produced is called the telial stage, because these are formed towards the end of the growing season.

The telial stage is considered the perfect stage of the Uredinales because it is in the teleutospores that karyogamy and meiosis takes place.

As the spores mature, the two nuclei in each cell of the teleutospore fuse to form a diploid nucleus. After the harvesting period mature teleutospores remain dormant on straw, stubble and survive even the severest winters.

Basidial stage

After the resting period the teleutospores germinates on return of favourable conditions – high humidity, presence of moisture and freezing condition prior to germination.

The teliospores germinate to give rise to the basidial stage in the life cycle of Puccinia.

Each cell of the teleutospore containing a diploid nucleus represents the probasidium or hypobasidium. A short, slender hypha of limited growth grows out through the germ pore from each cell, this is called the promycelium or epibasidium.

The diploid nucleus of the teleutospore migrates into the promycelium. There the diploid nucleus undergoes meiosis form four haploid nuclei. Septa appear between the nuclei dividing the epibasidium into four uninucleate haploid cells.

From each  of the three lower epibasidial cells develops a short narrow tube, the sterigma. From the terminal cell of the epibasidium the sterigma arises from the apex. The free tip of each sterigma swells to form a basidiospore.

Two out of the four basidiospores on each epibasidium are of plus strain and the other two of minus strain.

Each basidiospore is a small, unicellular, uninucleate haploid structure.

The basidiospores are forcibly discharged into air. They are carried by wind to the leaves of alternate host barberry which they infect. The basidiospores remain viable only for a few days. They cannot infect the wheat plant and thus perish soon if the alternate host is not available.

Life Cycle of Barberry Plant

The basidiospore germinates on the leaf of the alternate host – barberry provided the moisture and temperature conditions are suitable. Each basidiospore gives out a germtube, which enters the host tissue directly through the epidermis.

Once within the host tissue it grows vigorously and branches freely to form the primary mycelium, also called monokaryotic or haplomycelium. The primary mycelium is septate, uninucleate. The mycelial hyphae ramify in the intercellular spaces between the mesophyll cells of the leaf.

They produce haustoria which penetrate the cells of the host tissue and obtain nutrition for the growth of the mycelium. The basidiospores are either of plus or minus strain. Several basidiospores of different strain infect the same barberry leaf. Naturally mycelia will be to two different strains, and develop side by side.

Spermagonial or Pycnidial Stage

After 3-4 days of infection, the hyphae begin to collect beneath the upper epidermis. They form a dense mat. Fromt he mycelial mat arise groups of hyphae which develop into small, flask-shaped structures called the spermagonia or pycnidia. The pycnidia like the mycelia form which they arise, are of plus or minus strain.

When pycnidia mature, the infected areas become swollen and are seen as small, orange yellow bumps on the upper surface of infected leaf.

Each spermogonium consists of a wall surrounding a cavity. It opens to the upper surface of the host leaf through small pore called the ostiole. From the wall of the spermagonium arise three kinds of hyphae:

i.                 Spermatiophores or pycnidiophores:

Numerous, elongated, uninucleate, hyphae arise from the cells of the wall. They project into the cavity of the spermagonium and are called the spermaiophore are pycniosphores. They are closely packed and arranged in a palisade – like layer.

Each spermatiophore by successive divisions forms  number of small cells one after the other. These are spermatia or pycnidia. Each spermatium has a single nucleus and very little cytoplasm. The mature spermatia fall into the spermagonial cavity. They are non-motile and cannot infect either host.

ii.               Periphyses:

They are long, delicate sterile hyphae which develop near the ostiole form the spermagonial wall. They are unbranched, tapering, orange-coloured, and called the  periphyses. They project through and beyond the ostiole end.

iii.             Receptive hyphae

Adjacent to the ostiole and among the periphyses, develop another kind of hyphae. They are slender, delicate, cylindrical with blunt free tips. Being flexous these are named the receptive or flexuous hyphae.

Spermatisation:

The mature spermatia exude from the ostiole of spermagonium in a drop of sticky, thich liquid called nectar. The nectar with its scent and sugary content attracts the insects to the leaf. The spermatia stick to the leags of the visiting insects are thus are dispersed from leaf to leaf or from one spermagonium to another.

When a compatible spermatium or pycniospores is deposited on the receptive hyphae, the intervening wlls at the point of contact dissolve. The spermatium nucleus passes through the opening into the receptive hypha.

The spermatial nucleus reaches the basal cell of the receptive hyphae, which thus comes to possess two nuclei which lie side by side in a pair. This coming together of opposite strain ( - and + ) is called the spermatization.

One of these nuclei is of minus strain and the other of plus strain. This pair of nuclei of opposite strains is called a dikaryon.

The spermatial nuclei from the basal cells of the receptive hyphae by repeated mitotic divisions forms several nuclei. The daughter nuclei so produced are passed on to the rest of the cells of the mycelium through the septical pores of the hyphae. The result is that theentire mycelium becomes dikaryotic.

Aecidial or Aecial Stage

Along with the formation of spermagonium, the haploid primary mycelium also produces a globose mass of hyphae, within the lower epidermis. This mass is called aecial primordium.

Each aecial primordium consists of a closely packed theft of hyphae, called basal cells; and a group of larger parenchyma cells. As a result of spermatization, the basal cells of the aecial primordium become dikaryotic. Dikaryotization leads to formation of aecia and aeciospores.

The dikaryotized basal cells are called the aecidiospore mother cells. The aecidiospore mother cell increase in length. The two nuclei in it divide conjugately. A small daughter cell is then cut off at its terminal end and it is called the aeciospores initial. Two of the nuclei remain in the aecidiospore mother cell and other two pass into the aecidiospore initial. The initial cell increases in size and divides into two, upper bigger binucleate aecidiospore cell and lower smaller binucleate, sterile disjunctor or intercalary cell.

Each aecidiospore mother cell undergoes a series of such divisions and closely packed chains of cells are formed at the tips of the aecidiospore mother cells. The mass of aeciospores is surrounded by a membrane called peridium. All these structures form a cup – like aecium or aecial cup.

The yound aecium is closed and buried deep in the leaf tissue. When the aecium matures, the spore chain pushes through the roof of the peridium and the peridium hangs down the lower epidermis. The aecial cups are visible externally as circular spots of reddish purple colour on the ventral surface of the leaf.

Each aeciospores is a polyhedral, binucleate, unicellular, thin-walled, orange coloured structures. The spores absorb water, round off suddenly and thus are jerked out of the aecidium. They are disseminated by the wind. The aeciospores are unable to germinate on the host barberry plant on which they are produced. They infect wheat plant. Under suitable conditions, the aeciospores germinates and produce dikaryotic mycelium in wheat to repeat the life cycle.

Oedogonium

Oedogonium

                                                                                                                  Classification         (Fritsch1931)

                                  Class   – Chlorophyceae
                                                                                                                 Order -  Oedogoniales
                                                                                                                  Family -  Oedogoniaceae
                                                                                                                Genus – Oedogonium
Occurrence
Oedogonium (Gr Oedos-swelling, gonos – reproductive bodies) is a freshwater, filamentous algae. This genus was named by Link. The genus has 400 species.
It grows in ponds, lakes and shallow tanks. The filaments are attached to rocks, logs or epiphytic on aquatic plants ( e.g., Hydrilla) and other algae. Some species are terrestrial, growing on moist soils e.g., O. terrestris, O. randhawa.

Structure of the Thallus:
The thallus is multicellular and filamentous. The filaments are unbranched and uniseriate. The filament consists of a single row of elongated, cylindrical cells arranged end to end. All the cells of a filament appear more or less similar except the basal cell and the distal or apical cell.
The basal cell is modified to form a holdfast or hapteron. It is devoid of chloroplast. The holdfast is expanded into a flattened disc with finger like outgrowths or projections. It helps in attachment of the filament to the substratum.
The terminal or apical cell of the filament may be rounded, acuminate or sometimes prolonged to hair-like structure (e.g., O.ciliate). Thus, the filament show clear apical-basal polarity.

Cell Structure:
The cells are elongated and cylindrical with a slightly swollen or dilated upper end. The green cell consists of a thick, rigid cell wall enclosing the protoplasts.
The cell wall is made up of three layers; an outer chitinous, a middle layer of pectin and an inner layer of cellulose. There is no mucilage on the surface of the filament.
The centre of the cell is occupied by a large vacuole containing the cell sap. The protoplast forms a thin layer in between the central vacuole and the cellulose layer of the cell wall.
There is a single, large, reticulate chloroplast present in the protoplasm. The chloroplast extends from one end of the cell to the other. The strands of the chloroplast are parallel to the long axis of the cell. A number of pyrenoids are characteristically present in the chloroplast particularly in the region of intersections.
There is a single large parietal nucleus which lies near the middle of the cell embedded in the cytoplasm just within the chloroplast. The nucleus is haploid.
Growth and cell division :
Growth in Oedogonium takes places as a result of cell division which is largely intercalary. Only certain cells in the filament divide.
Every cell division is accompanied by the formation of a specialized structure called the cap cell. The cell division in Oedogonium is peculiar and unique.
The cell division starts with the movement of the peripheral nucleus to the centre of the cell. A ring like thickening of hemicellulose develops at the apical end of the cell. The ring gradually increase in thickness and becomes grooved.
By this time, the nucleus divide mitotically. The division of the nucleus is followed by the formation of a floating cytoplasmic strand between the two daughter nuclei. For sometime, the cytoplasmic strand remains unconnected with the later wall.
The outer and the middle layers external to the groove then ruptures allowing the free elongation of the ring. Consequently, the cell elongates with the distal half having a new membrane formed from the stretched new wall material of the thickened ring. It is intercalated between the upper and the lower ends of the old rupture wall.
At the same time, the septum is pushed upwards and finally becomes fixed near the lower end of the intercalated membrane. The upper daughter cell thus formed has now a new bounding wall consisting mainly of the intercalated membrane formed from the thickened ring and the newly synthesized piece. There is however, a portion of the ruptured parent cell wall fitting like a cap at its upper end. This forms a characteristic ring-like mark, the apical ring or apical ring.
The upper daughter cell with its apical cell is called cap cell and the lower daughter cell is called the sheath cell. Only the cells with cap divide again. After each division a new cap is formed. Thus, the number of apical rings the cap cells contains denotes the number of divisions the cell has undergone.
Reproduction
All three types, Vegetative, Asexual and Sexual reproduction are seen in Oedogonium.
Vegetative Reproduction
The vegetative reproduction takes place by means of fragmentation. The fragmentation takes place by (i) Dying out of some cell here and there in the filament, (ii) through accidental breaking, (iii) formation of zoospores or gametes and liberation because of wall splitting. Each fragment by cell division and growth develops into a new filament.
Asexual Reproduction
In Oedogonium, asexual reproduction takes place by three kinds of asexual spores (i) Zoospores, (ii) Akinites and (iii) Aplanospores
Zoospores
Zoospore formation is the most common and effective method of asexual reproduction. They are produced singly in the specialized cell called zoosporangium. Any cap cell usually , the recently divided onw which contains abundant reserved food material may become zoosporangium.
The entire protoplast of the zoosporangium contracts from the cell wall and becomes a rounded mass. The nucleus moves towards one side of the protoplast.
A semi-circular, colourless area appears on one side due to receding of the chloroplast towards other side. A single or double row of blepharoplast granules then appear at the base of the hyaline area. The basal granules are connected by fibrous strands to form complete circular ring.
From each granule arise a single flagellum. In this way a ring of flagella is formed around the base of colourless beak like area of the protoplast.
With the formation of zoospore, the cell wall near the upper end splits transversely and the upper portion of cell is lifted off like a lid. The mature zoospores enclosed in a delicate mucilage vesicle, slips out through the aperture.
The mucilaginous vesicle soon disappears and makes the zoospore swim freely in the water. The liberated zoospore is a deep green, spherical or pear shaped. It has a ring of short flagella at the base of colourless, beak like anterior end. This kind of flagellar arrangement is called stephanokont.
The zoospore possesses an eye spot, a chloroplast, a haploid nucleus and numerous vacuoles. The liberated zoospore remains motile for about an hour. Then it settles down, attaches itself to the substratum by colourless flagellar end. It withdraws the flagella and secrets a cell wall.
The one celled zoospore divides transversely forming an basal cell and a apical cell. The basal cell remains colourless and doesnot divide again. It develops into a cylindrical hapteron or holdfast. The upper cell by the normal methods of division and redivision of its daughter cells forms the new filament.
Akinete Formation
In some species of Oedogonium, during unfavourable conditions, resting cells or akinetes are formed. They are thick walled, reddish brown, rounded or oval structures. They are formed in chains, each inside an inflated cell resembling an oogonium.
The akinetes are rich in starch as reserve food material and reddish orange oil. On returning of favourable condition each akinete germinates into a new filament.
Aplanospore formation
In some species of Oedogonium aplanospores are also formed. They are slightly oblong or spherical and formed one or two in each cell.
 Sexual Reproduction
The sexual reproduction in Oedogonium is Oogamous type. The sexual cells or the gametes are structurally and physiologically different. They are produced in highly specialized reproductive organs, the gametangia.
The male gametangia is called the antheridium and the female gametangia is called the oogonium. Depending on the distribution of sex organs, species of Oedogonium are grouped into two categories: 1. Macrandrous species and 2. Nannandrous species.
Macrandrous species:
The species of Oedogonium that produces antheridia and oogonia in normal filament is called Macrandrous species. They may be monoecious (O.fragile) producing antheridia and oogonia on the same filament or dioecious (O. crissum, O, aquaticum) producing antheridia and oogonia on different filaments.
Nannandrous species:
The species of Oedogonium that produce oogonium in normal filament and antheridium in small, dwarf filament or nannadria is called Nannadrous species.
Sexual Reproduction in Macrandous forms:
The development of antheridia and oogonia is similar in both monoecious and dioecious species.
Antheridia
Antheridia are formed in either terminal or intercalary cell of the filament. Any cap cell may function as antheridial mother cell. The antheridial mother cell divides into two unequal cells, the upper small antheridium and the lower larger sister cell.
The sister cell divides again repeatedly, so as to give rise a series of 2 to 40 antheridia. The protoplast of each antheridia divides mitotically, by transverse or vertical wall into two haploid daughter protoplasts. Each protoplast becomes pear-shaped and develops a ring of flagella around a colourless portion at its one end and metamorphoses into an antherozoid or sperm. Thus two antherozoids are produced in each antheridium.
The pattern of division decides the arrangement of antherozoids i.e., they may lie superimoposed (one above the other) or side by sied in an antheridium.
The wall of antheridium ruptures transversely and two antherozoids are freed into a thin vesicle. Soon, the vesicles dissolves and two antherozoids swim freely in the water. The liberated sperms are pale green, yellowish green spherical bodies. Each has a sub-apical ring of short flagella at the base of colourless, beak-like antherior end.
The morphology, flagellation and liberation mechanism of the antherozoids is similar to the zoospores. However, antherozoids are smaller in size and have fewer flagella. The liberated antherozoids swim freely and finally reach the oogonia.
Oogonia
The oogonia are highly differentiated female gametangia. Each oogonium develops from an actively growing cap cell called the oogonial mother cell.
The oogonial mother cell divides by a transverse wall into two cells. The upper cell is riches in cytoplasm, has larger nucleus than the lower cell. It functions as an oogonium. It has one or more caps at the upper end.
The lower cell supports the oogonial cell and is called suffultory cell or supporting cell. It often remains undivided. In some species, it again functions as an oogonium mother cell and undergoes further divisions to form a chain of two or three or four oogonia.
The oogonium becomes prominently enlarged and is filled with reserve food material. The oogonia is always  much broader than filaments a characteristic feature of order Oedogoniales.
The entire protoplast is converted into a single ovum. Owing to presence of chlorophyll the ovum is green. It is non-motile and retained within the oogonium. Prior to fertilization, the ovum or egg protoplast slightly receds from the oogonial wall to form a small clear patch, the receptive spot. The oogonial wall develops a small pore or transverse slit near the anterior end above the receptive spot. It forms a sort of a conduit leading down to the ovum and provides a passage to antherozoids entrance during fertilization.
Thus, a mature oogonium complex consists of an oogonium and a supporting cell. Enclosed inside the wall are a large nucleus and an anterior receptive spot. The ovum remains laden with reserve food material.

Sexual Reproduction in Nannadrous forms:
The nannandrous species are dioecious. They exhibit a curious dimorphism of sexual plants. The oogonia are produced on normal, large filaments. The antheridia are produced by special, short, few celled filament called the dwarf or nannadria.
The dwarf male are produced by the germination of peculiar type of motile spores called the androspores. The androspores are produced within cells called the androsporangia.
If oogonia and androsporangia are present in the same plant, the condition is called gynandrosporous, e.g., O. concatenatum. The species in which androsporangia are borne in a separate filament, it is named as idioandrosporous, e.g., O. iyengarii.

Structure and germination of Androspores
Androsporangia are similar to antheridia in development and are produced by unequal division of mother cell but are rather larger. The androsporangia are flat, discoid cells. Its protoplast metamorphoses into a single androspore.
The androspore are motile and are provided with a sub-polar crown of flagella. They are larger than antherozoids but smaller than zoospores. On liberation, the androspore is surrounded by the mucilaginous vesicle. This vesicle soon vanishes and andropsore swims freely till it reaches and attaches itself to the wall of the oogonium or supporting cell.
The attached androspore germinates on the oogonium or supporting cell producing 2-3 celled filament called the dwarf male or nannadrium. The lower, rhizoid-like elongated cell of the dwarf male is called the stalk. The stalk cell cuts off one or more cells at its tip. These are antheridia.
The protoplast of antheridium divides mitotically into two daughter protoplasts. Each daughter protoplast develops a ring of many flagella at one end and forms a multiflagellated sperm or antherozoid.
The antherozoids are liberated either by the disorganization of the antheridial cell or by the separation of a cap like lid at the top.
Oogonium:
Oogonial development in Nannadrous species is similar to that of Macrandrous species.
Fertilisation:
It is similar in both Nannarous and Macrandrous forms. The antherozoids swimming in water enter the oogonium through a pore or tansverse slit in the oogonial wall. There is a chaemotatic attraction between the antherozoids and oogonium (Hoffman 1973)
One of the antherozoid, probably the first to arrive enters the egg at the receptive spot. The male and female nuclei in the egg fuse to form the diploid nucleus and a diploid zygote is formed.
Oospore:
The zygote secretes a 2-3 layered thick wall to form an oospore. Due to accumulation of reddish oil oospore appears red in colour. The oospore is liberated from the filament by the decay of the oogonial wall and rests on the mud at the bottom of the pond where it enters into a period of rest.
Germination of Oospore:
After a period of rest, the oospore germinates. Prior to germination, the diploid oospore nucleus undergoes zygotic meiosis to form four haploid nuclei. The protoplast loses, its red colour and turns green. The haploid nuclei are organized into four uninucleate daughter protoplasts by cleavage of the oospore protoplast.
Soon, each haploid daughter protoplasts furnishes itself with a crown of flagella to become a motile spore resembling the zoospore of the asexual stage. It may be called a meiozoospore.
The oospore wall ruptures to liberate the mature, motile meiozoospores. They are at first surrounded by a delicate vesicle. The vesicle soon disappears. The liberated meiozoospores swims about for a while and then settles down to germinate. They grow into haploid Oedogonium plants. In dioecious species, two zoospores develop into male and two into female filaments, eg., O.plagiostomum.
Life Cycle:
The life cycle is known as haplontic because the plant is haploid. The only diploid stage is the zygote which soon undergoes meiosis resulting in 4 haploid zoospores. The zoospores germinate into new haploid filaments.