Histologic Changes in Virus-Infected Plants

Questions and Answers

What occurs during phenotypic mixing in virus strains?

RNA of one strain is replaced with that of another strain.

Both genotype and phenotype are changed.

Only the genotype of the virus is altered.

Particles contain RNA from one strain clothed with proteins from another strain. (correct)

How does phenotypic mixing differ from genetic recombination?

Phenotypic mixing changes both genotype and phenotype.

Only phenotype is altered in phenotypic mixing. (correct)

Genetic recombination occurs naturally, while phenotypic mixing does not.

Both processes result in hybrid viruses.

What factor can influence virus variability and the appearance of new strains?

The time of year the viruses are studied.

The species of the host plant.

Humidity levels in the environment.

The temperature at which the plant is grown. (correct)

What do temperature-sensitive mutants impact during virus reproduction?

Synthesis of envelope proteins. Signup and view all the answers

What is a possible consequence of the emergence of hybrid viral particles in plants?

Increased virulence and decreased yield. Signup and view all the answers

What role do different strains of the same virus play with regards to vector species?

They can be adapted to various vector species. Signup and view all the answers

What specific changes occur in temperature-sensitive mutants?

Amino acid substitutions lead to impaired functionality. Signup and view all the answers

Which of the following is a characteristic of phenotypic mixing?

It results in particles with mixed protein coats but unchanged RNA. Signup and view all the answers

What phenomenon can lead to the emergence of aggressive viral strains?

Natural mixed populations of viruses. Signup and view all the answers

What happens to strains that cannot reproduce efficiently at higher temperatures?

They have amino acid substitutions in their structural proteins. Signup and view all the answers

Which method allows for the detection of stable bacilliform and filamentous viruses through direct immersion?

Crushed suspension method Signup and view all the answers

What is the primary benefit of using a 2% glutaraldehyde solution in virus diagnostics?

It stabilizes the virions in leaf tissues Signup and view all the answers

What is the role of reverse transcription in the polymerase chain reaction (PCR) method for diagnosing viruses with RNA genomes?

It converts RNA into complementary DNA (cDNA) Signup and view all the answers

Which statement accurately describes the use of negative contrast in virus preparation?

It is used for stabilizing unstable virions during preparation Signup and view all the answers

What type of inclusions were first discovered by D.I. Ivanovsky?

X-bodies Signup and view all the answers

Which chemical can induce the formation of viral inclusions by changing the pH of cell sap?

Acetic acid Signup and view all the answers

What factor contributes to the high sensitivity and selectivity of the PCR method for virus detection?

The ability to amplify a specific DNA sequence Signup and view all the answers

Which of the following is NOT a characteristic of the crushed suspension method?

It can be used for any type of virus Signup and view all the answers

Why is the polymerase chain reaction (PCR) considered expensive?

It needs specialized equipment and materials Signup and view all the answers

Which method combines serology with electron microscopy for virus diagnostics?

Immunoelectron microscopy Signup and view all the answers

Study Notes

Histologic and Cytologic Changes

Virus-infected plants exhibit external features due to histological and cytological modifications in infected cells.
Structural analysis performed by phytovirologists utilizes light, phase-contrast, and electron microscopy.
Histological changes include hypertrophy and hyperplasia, leading to tumor formation and enation.
Example viruses include wound tumor virus, which causes tumors on various plants, and tomato aspermia resulting in enations.
Many viruses affect the vascular system, resulting in tilla formation, cell death, and associated plant wilting.
Symptoms include delayed outflow of assimilates, necrosis in different plant parts, and overall plant dwarfism.
Viral infections may lead to chlorosis and mosaic coloration in leaves due to the formation of vesicles around chloroplasts and chloroplast deformation.
Viruses like tobraviruses also cause mitochondrial aggregation into inclusions.
Viral particles can be found in cytoplasm, chloroplasts, nuclei, and near mitochondria, often as inclusion bodies with crystalline or amorphous structures.

Physiological Changes in Virus-Infected Plants

Viral infections disrupt metabolic activities, particularly affecting water regime, photosynthesis, and nitrogen metabolism.
Changes in the water regime due to transpiration intensity decrease can lead to water supply issues and plant death.
Transpiration reduction results from necrosis affecting leaf surfaces and conductive system alterations.
Photosynthetic activity declines as chloroplasts are destroyed or altered by viral infection, leading to chlorophyll degradation.
The reduction in photosynthesis correlates with the virus strain, phase of the disease, and environmental conditions.
Carbohydrate metabolism is directly impacted, resulting in decreased carbohydrate content and transport disruption when the phloem is affected, causing leaves to thicken and become brittle.
Nitrogen metabolism disturbances are common, with increased proteolytic activity and soluble nitrogen content observed in infected plants.
Infected plants show increased respiration activity initially, attributed to the host plant's defense mechanisms, eventually resulting in decreased respiration intensity as virion synthesis escalates.
Viral infections often induce growth disturbances, leading to abnormal shapes and excessive bud formation.

Properties of Phytoviruses

Antigenicity, primarily determined by the viral protein coat, is crucial for diagnosing viral infections.
Viruses trigger antibody production in immunized animals, utilized for serological testing.
Immunogenicity allows antigens to stimulate specific antibodies that react with them.
Variability of viruses leads to the emergence of new strains capable of infecting resistant crops, defined taxonomically as 'strains.'
Strains exhibit variations in morphology, antigenic affinity, host range, pathogenicity, and symptoms.
More than 200 strains of BTM have been identified, each demonstrating different virulent behaviors and symptoms.
Viral mutations, often caused by environmental factors like UV radiation and chemicals, contribute to strain variability which can affect RNA integrity.
Genetic recombination occurs when RNA from different strains exchanges during simultaneous infections, creating hybrid strains with new properties.
The temperature at which a plant is grown can affect virus replication and mutation rates, leading to the development of temperature-sensitive mutants.

Methods of Diagnosing Phytoviruses

Various methods for diagnosing phytoviruses include visual inspection, infectivity tests, plant-indicator methods, serological techniques, electron microscopy, and polymerase chain reaction (PCR).

Visual Method of Diagnosis

Diagnosis through external symptoms provides initial insights into viral diseases in plants across diverse biocenosis conditions.
Attention must be paid to weeds as potential virus reservoirs and invertebrates as vectors.

Determining Infectivity

Establishing infectivity requires demonstrating the pathogen's presence through artificial infection methods.
Key methods for confirming viral diseases include mechanical inoculation, vector transmission, and inoculation through dodder.

Inoculation Techniques

Inoculum preparation includes stabilizing the virus with specific buffers and stabilizers, and it is often applied using techniques like leaf rubbing.
Adsorbents can be mixed into the inoculum to enhance stability.
Symptoms can develop from 3 to 30 days post-inoculation, varying based on the virus.

Plant-Indicator Method

Indicator plants react visibly to virus infection, allowing for easier identification of specific viruses.
Common indicator plant families include Solanaceae, Chenopodiaceae, and Cucurbitaceae.
Indicator plants are classified by their response type: localized, systemic, and mixed reactions.

Serological Method

Developed in 1927, the serological method relies on the antigen-antibody interaction.
Antigens are primarily proteins and polysaccharides and provoke specific antibody production in the host.
Diagnostic serums are created by injecting viral antigens into rabbits, followed by the purification of antibodies for testing against samples.

ELISA (Enzyme-Linked Immunosorbent Assay)

ELISA is a leading laboratory test for identifying specific antibodies and quantifying them in various biological materials.
Known for its high sensitivity (90%) and specificity (95%), ELISA is widely used in multiple fields.
The method includes the adsorption of antibodies to plates, addition of plant sap, and measurement of enzyme activity to determine virus concentration.

Other Advanced Methods

Radial diffusion and latex methods increase sensitivity of virus detection through enhanced agglutination reactions.
Radioimmunologic analysis utilizes radioactive isotopes to study antigen properties.
Immunofluorescence involves covalent attachment of antibodies to fluorescent dyes, allowing visualization under a fluorescent microscope.

Practical Considerations

Proper isolation and sterilization procedures are crucial for working with indicator plants.
Environmental conditions such as temperature and lighting influence the sensitivity and responsiveness of indicator plants to viral infections.
Various physical and biochemical methods are used to enhance detection, ensuring identification of pathogens even at low concentrations.### Molecular Technologies in Phytosanitary Control
Molecular technologies increasingly replace traditional and serological methods in the phytosanitary control of agricultural plants.
Offer 10-100 times higher sensitivity compared to ELISA.

Electron Microscopy in Viral Disease Diagnosis

Used for diagnosing viral diseases and studying virus biology, plant-virus-vector relationships, and virion concentration.
First electron micrograph of viral transmission models (VTMs) and citrus vein clearing (CVC) viruses captured in 1939.
Biological samples must have high electrical conductivity, resistance to vacuum, and a large atomic mass.
Fresh materials are critical for the preparation of biological samples to be viewed under an electron microscope.
Contrast techniques like metal sputtering (with chromium, tungsten, gold, etc.) enhance visibility of virions.

Preparation Techniques for Electron Microscopy

Immersion Method: Suitable for filamentous and bacilliform viruses; involves immersing freshly cut leaf edges in distilled water.
Crushed Suspension Method: Involves crushing leaf samples to create a homogenous suspension, then applying it to a grid.

Stabilization Methods for Virions

G.M. Razvyazkina and G.P. Polyakova introduced a negative contrasting method for the Russian mosaic virus.
E.I. Larina enhanced this method by stabilizing virions with glutaraldehyde before preparing samples.

Other Diagnosis Techniques

Ultrathin sections of plant and vector tissues can be prepared using ultramicrotomes.
Immunoelectron microscopy combines serology with electron microscopy, treating substrate films with specific antiserum.

Viral Inclusions

Discovered by D.I. Ivanovsky, inclusions can be crystalline or amorphous, indicating intensive viral replication.
Induced by altering pH with acid solutions, which can be visualized using light or electron microscopy.

Polymerase Chain Reaction (PCR) Method

PCR amplifies specific DNA sequences in vitro; applicable to many phytoviruses that contain RNA.
Reverse transcription into complementary DNA (cDNA) followed by amplification using thermostable DNA polymerase.
Involves repeated cycles of denaturation, primer annealing, and elongation, resulting in exponential DNA increase.
Although PCR requires special equipment, its high sensitivity and speed make it suitable for widespread use in phytopathology.
Notable applications include diagnostics of viral pathogens in strawberries and detection of the genome of plum pox potyvirus.

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Description

Explore the histological and cytological changes occurring in virus-infected plants. This quiz covers the structural effects on plants due to viral infections and examines methodologies such as light and electron microscopy used by phytovirologists. Learn about phenomena like hypertrophy, hyperplasia, and their implications.