ASEMINAR

ONPLANT AND ANIMAL VIRUSES

PROF. J. P. SHARMA ( DIRECTOR) PRESENTED BY

DR. R. K. RAO (PRINCIPAL) NIKITA DEWANGAN

GUIDED BY - RACHANA TIWARI M.SC. 1ST SEMESTER

BIOTECTNOLOGY

G.D. RUNGTA COLLEGE OF SCIENCE & TECHNOLOGY

KOHKA-KURUD, BHILAI DURG (C.G.)

PLANT AND ANIMAL VIRUSE

SYNOPSIS

INTRODUCTION

HISTORY

MORPHOLOGY OF VIRUSES

PLANT VIRUS

TOBACCO MOSAIC VIRUS (TMV)

1. SYMPTOMS

2. VIRUS STRUCTURE

3. PROTEIN SYNTHESIS

4. TRANSMISSION

5. MODE OF ACTION OF TMV

EFFECT OF VIRUS ON PLANT

ANIMAL VIRUS

CLASSIFICATION

DNA CONTAINING - SV 40 VIRUS

RNA CONTAINING - RHABDOVIRUS

CONCLUSION

REFRENCES

INTRODUCTION

Viruses are small obligate intracellular parasites which by definition contain either a

RNA or a DNA genome , surrounded by a protective virus – coded protein coat.

HISTORY

Edward Jenner (1798) introduced the term virus in microbiology.

Virus Greek means ‘’ poison’’.

In 1892 for the first time a Russian botanist DMITRI IWANOWSKI discover the virus.

MORPHOLOGY OF VIRUSES

SHAPE - Viruses are of different shapes such as spherical or cuboid ( adenovirus) ,

elongated (potato viruses), flexuous or coiled (beet yellow), bullet shaped (rabies virus),

filamentous ( bacteriophages M13) , pleomorphic.

SIZE - Variable size from 20 nm to 300 nm in diameter.

They are smallest than bacteria, some are slightly larger than protein and nucleic acid

molecules and some are about of the same size ( small pox virus) as the smallest

bacterium and some virus slightly large (300 – 400 nm).

VIRAL STRUCTURE

I. HELICAL ( CYLINDRICAL) VIRUSES -

The helical viruses are elongated, rod shaped, rigid or flexible.

There capsid is a hollow cylinder with a helical structure.

Capsid consists of monomers arranged helically in rotational axis.

The consist may be naked e.g. TMV or envelope e.g. influenza virus.

Fig ; - 1 ,structure of helical virus

II. POLYHEDRAL ( ICOSAHEDRAL) VIRUSES -

Polyhedral structure has the three possible symmetries such as

tetrahedral, octahedral and icosahedral.

The viruses are more or less spherical, therefore icosahedral symmetry is

the best one for packaging and bonding of subunits.

The capsomers of each face form an equatorial triangles and 12

intersepting point or corners.

They consist naked capsid e.g. adenovirus or envelope e.g. herpes simplex

virus.

Fig ; 2 , structure of polyhedral virus

III. COMPLEX VIRUSES -

The viruses which have the unidentifiable capsids or have the capsids with

additional structures are called complex viruses.

Capsids not clearly identified e.g. vaccinia virus etc.

Capsids to which some other structure are attached e.g. some

bacteriophages etc.

Fig ; - 3 structure of complex virus

ENVELOPE -

There are certain plant and animal viruses and bacteriophage both icosahedral

and helical , which are surrounded by a thin membranous envelope. This

envelope is about 10-15 µm thick . it is made up of protein , lipids and

carbohydrates.

Which are combined to form glycoprotein and lipoprotein.

Lipids provide flexibility to the shape , therefore viruses look of variable size

and shape.

Protein component of the envelope is of viral origin and lipid and carbohydrate

may be the feature of host membrane.

THE PLANT VIRUS

Plant viruses are viruses that affect plants , like all other viruses plant viruses are

obligate intracellular parasites that do not have the molecular machinery to replicate

without a pathogenic to higher plants.

1. TOBACCO MOSAIC VIRUS ( TMV)

TMV is the most serious pathogen causing mosaic on tobacco leaves.

It is transmitted by artificial inoculation but not by insect vectors.

TMV is the most resistant virus known so far of which the thermal death point is 90 ºc

for 10 minutes.

This is the first virus that was crystallized in 1935 by W.M. STANLEY in the U.S.A.

SYMPTOMS

TMV damages the salanaceous plants. However, it can infect the other plant too.

After infection, it developes symptoms of lightning of leaf colour along the veins in early

stages.

There after it turns into light and dark green mosaic symptoms.

Along the veins green colour turns into dark green and the internal region turns into

chlorotic.

Some times dark green blisters appear in the leaf blade.

The virus reduces the yield as well as quality of the products.

VIRUS STRUCTURE

Franklin et al (1957) have described the structure of TMV.

It is rod shaped helical virus measuring about 280×150µm with a molecular weight of 39

×106 daltons.

The virion is made up of 2130 protein subunit of identical size.

The protein subunits are arranged around a central hole of 4nm (40 Å).

Each protein subunit is made up of a single polypeptide chain which possesses 158 amino

acids the molecular weight 17500 daltons.

Inside the protein capsid there is a single stranded RNA molecule which is also spirally

coiled to form helix.

Virus RNA consists of 6500 nucleotides.

In one turn the RNA contain 49 nucleotides.

Total numbers of protein subunit counting in three turns is 49.

PROTEIN SYNTHESIS

The virus RNA utilizes the amino acids ribosomes and tRNA of the host and

synthesizes the complementary strand and protein i.e. coat proteins of 17500 daltons and

two other polypeptides.

The ratio of nucleic acid and protein differs with each virus.

Nucleic acid is about 5-40% of the virus and protein 60-70%.

Each protein subunit of TMV consists of 158 amino acid making a total number to about

17531.

TRANSMISSION

TMV is transmitted through the cell sap of host and enters a new host through wound

incision.

Wound is caused in plant due to various cultural operations such as clipping or topping

the shoot.

It is also transmitted by wind and water.

MODE OF ACTION

In the cell the tobacco mosaic virus form crystals in the chloroplast and accumulate.

Resulting pigment of cell which produces colour get affected, colour may turn to colour

less.

fig;4, structure of tobacco mosaic virus

EFFECT OF VIRUSES ON PLANT :-

1 . EXTERNAL SYMPTOMS :-

a) MOSAIC - Development of light (chlorosis) and dark green area on leaves

are due to disturbances of chloroplast and decrease in chlorophyll content.

b) CHLOROSIS , VEIN CLEARING AND VEIN BANDING -

Vein clearing symptoms develop adjacent to veins before chlorosis of tissue.

While broader bands of green tissue in chlorosis or necrosis is called vein

banding.

c) RINGSPOT - Ringspot is characterized by formation of concentric rings

or broken rings of infected dead cells. The ringspot may be chlorotic rings

rather than necrotic rings.

d) NECROSIS - Besides localized cell death in necrotic local lesion or

ringspots , necrosis in certain areas organs e.g. leaves, fruits, seeds , tubes or

entire plant. Affected leaves shows scattered necrotic patches of dead tissue.

e) LEAF ABNORMALITIES - Due to virus infection leaves show

abnormal growth like leaf curling, leaf rolling, crinkling, puckering

(depression)etc. the other abnormalities may also develop in leaves such as

smaller blistered and thickened leaves.

f) FLOWER SYMPTOMS - The colour breaking means streaks or sector

of tissue with such colour that are different from the normal one. This happens

due to loss or increase of anthocyanin pigment in petals.

2. INTERNAL SYMPTOMS

a) HISTOLOGICAL ABNORMALITIES - In leaves showing

mosaic symptoms. Mesophyl cells are smaller and less differentiated.

b) CYTOLOGICAL ABNOMALITIES - Many cytological

abnormalities are seen when virus infected cell are studied cytologically.

Moreover some viruses affect specific organelles only.

Tymovirus induces formation of marginal verticles in chloroplasts.

Tobacco rattle virus modifies mitochondria and aggregates to form

inclusion bodies.

TMV particles are found in cytoplasm where as TMV of strain U5

are round in chloroplast and nuclei.

Chloroplasts may be rounded swollen and clumped together in the

cells . chloroplast may be fragmented and colour may turn to colour

less.

THE ANIMAL VIRUSES

CLASSIFICATION - On the basis of types of nucleic acid the classification of

viruses are as :-

Class 1. dsDNA viruses

Adenoviruses genome size 35-40 kb.

Herpes virus genome size 120- 200 kb.

Papovavirus genome size 5-8 kb.

Pox virus genome size 120-300 kb.

Class 2. ssDNA viruses

Parvovirus genome size 4-5kb.

Class 3. (+) ss RNA viruses

Coranavirus genome size 16-21 kb.

Picorna virus genome size 7 kb.

Togavirus genome size 17 kb.

Class 4. (-) ssRNA viruses

Paramyxoviruses genome size 15 kb.

Rhabdovirus genome size 12- 1 kb.

Orthomyxovirus genome size 14 kb.

Class 5. dsRNA viruses

Reovirus genome size 18-30 kb.

Class 6. RNA – DNA viruses

In these viruses (+) ssRNA direct synthesis of (-) DNA which in turn acts as

template for the transcription of mRNA .

Retrovirus genome 7-10 kb.

Class 7. DNA- RNA viruses

This group consists of DNA containing hepatitis B viruses.

The DNA containing animal virus : - SV40 virus

SV40 is an oncogenic virus.

It is naked and icosahedral in morphology with a diameter of 45nm.

Capsid consists of 72 capsomeres.

SV40 is similar to polyoma virus in size and structure.

Polyoma is associated with tumour in mice.

a) REPLICATION

Virus enters the cell and directly migrats to the nucleus and then mutation cause

in genetic material of host resulting normal activity of cell inhibit which causes

tumor.

Replication of viral DNA takes place inside the nucleus.

Before the replication begins early proteins are synthesized in the nucleus of the

infected cells.

The ds- DNA in its native form is supercoiled ( i.e. covalently closed circle ) .

helix having the sedimentation coefficient of 215.

Total G+C content of acid is 41%.

After breaking the phosphodiester bond single stranded DNA helix is converted

into a relaxed circular form.

This form has the sedimentation coefficient of 165. A linear form ( of 145) is

formed after double stranded break in the supercoil.

Fig ; 5, SV40 virus structure

The RNA containing virus :- Rhabdovirus

Rhabdovirus are bullet shaped with one flattened end.

Rhabdo is a Greek word which means a rod but the term rod is not accurate to its

morphology.

Rhabdoviruses are found in vertebrates, invertebrates and plant.

The example of rhabdovirus are rabies virus, vesicular stromatitis virus (VSV)

and potato yellow dwarf virus.

VSV is the most extensively studied rhabdovirus.

It is a mild pathogen to cattle. Vesicular stromatitis virus affect the central

nervous system so host parasite do abnormal behavior.

VSV contain a nucleocapsid (70 – 180) which is envelope on its outer surface,

consists of numerous spikes of glycoprotein on inner surface and the membrane

(M) protein.

Inside the nucleocapsid, there is a (-) ssRNA molecule which is cylindrically

coiled to make the core hollow.

The RNA polymerase uses (-) RNA strand as the template and produce (+) RNA

strand.

The (+) RNA strand acts as mRNA and as a template for the synthesis of viral

RNA.

Fig; 6, structure of Rhabdovirus

CONCLUSION

It is concluded that a virus is a non- cellualar particle made up to genetic material and

protein that can invade living cell.

Virus can replicate its genetic material in the host cell.

Virus can naked as well as have envelope.

Virus can infect all type of life – animal , plant , human and cause diseases.

REFRENCES

R. C. DUBEY 2006 MICROBIOLOGY

SOME CONTENT FROM NET : - www.ncbi.nlm.nih.gov/books/NBK8174/virus

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