This document summarizes the movement and physiology of virus-infected plants. It discusses three types of virus movement: intracellular, intercellular, and long-distance. Intracellular movement relies on the endoplasmic reticulum and cytoskeleton, while intercellular movement occurs through plasmodesmata connecting adjacent cells. Long-distance movement involves viruses entering the vascular system and moving systemically through the plant. It also examines effects on the infected plant's photosynthesis, respiration, membrane permeability, translocation, and transcription/translation, such as reduced chlorophyll and sucrose content as well as increased respiration and permeability.

1. Movement of viruses,
physiology of virus
infected plants
N. H. SHANKAR REDDY
Ph.D., Plant Pathology
Annamalai University

2. • From the site of infection, the virus first moves to adjascent cells, from there they
move to vascular system, there by systemic spread of the virus takes place from
root to distal part of young unfurling leaves
• In the case of vector transmission of phloem limited virus, the viruses are directly
delivered into the phloem paranchyma by the vector.

3. The movement of the virus can be
categorized into three types
1. Intracellular
2. Intercellular (Cell to cell)
3. Long distance.

4. 1. Intracellular
• Viruses are dependent on endoplasmic reticulum and the
cytoskeleton of the host (consisting of microtubules and
microfilaments) for movement within the cell.

5. 2. Intracellular movement
• In cell to cell movement of the virus is through the cytoplasmic connections
called plasmadesmata between the walls of the adjascent cells.
• Plasmadesmata: there are cytoplasmic connections between the adjascent
cells constituting systemic continuous throughout the plant

6. Movement proteins :
• There are protein encoded by the viral genome which
are involved in movement function. They have 3 main
basic features.
1. They bind to either ssRNA or ssDNA.
2. They are associated with plasmadesmata;
either modify SEL or form tubules.
3. They interact with cytoskeleton protein .
4. They transport themselves and the viral
genome from cell to cell.

7. 4 types of movement proteins
1. Type I - TMV
2. Type II - Its seen in Hordeiviruses and potexviruses. The movement is
governed by three overlapping ORFs known as triple gene block. (TGB—
TGR1, TGR2 and TGR3).
3. Type III - Seen potyvirus,
4. Type IV - Commovirus, Caulimovirus

8. 3. Long distance/ systemic movement
• Virus enter vascular system after crossing the bundle sheath cells
• Form vascular (phloem paranchyma), virus reaches the companion cells
• From companion cells the virus reaches the nucleate sieve elements- from
where it can move entire plants
• Virus are unloaded/ transported only through major veins. They exit from
phloem (unloading only from major veins) some of the viruses are retained in
phloem only. Virus does not enter apical meristem

9. physiology of virus infected
plants
Photosynthesis
Respiration
Permeability of cell membranes
Translocation of water and nutrients
Transcription and translation

10. i. Photosynthesis
The influence of virus infection
• Reduction of chloroplast numbers
• Reduction in chlorophyll content
• Chloroplast abnormalities
• Reduction in photochemical activity
• Stimulating CO2 incorporation at early stage of infection, but declined after
virus infection for several days.
• Reduction in sucrose content

11. ii. Respiration
• Pathological respiration induced by viruses
Respiration rate
• Nonhypersensitive hosts (systemic hosts)
Slightly increase in respiration rate of inoculated leaves
• Hypersensitive hosts
A much more pronounced increase in respiration activity than
systemic hosts.

12. iii. Permeability of cell membranes
• Pathogens can change the permeability of host cell membranes by
mechanical injury, enzymatic degradation, or toxins.

13. iv. Translocation of water and nutrients
Plants infected by viruses
• Although there are exceptions, virus infection generally leads to a
reduction in transpiration rate, which is often correlated with a reduced leaf
stomatal aperture.
• Accumulation of carbohydrates in leaf tissue is a characteristic of severe
virus diseases. It is usually accompanied by phloem necrosis and/or
gummosis, particularly in the later stage of disease.

14. v. Transcription and translation
• Transcription and translation of host cells usually increase in response to
pathogen infection, but with a higher level for resistant plants, since the
resistant plants need to proceed the defense reactions.

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