Description on Chemical composition and physical properties of plant viruses

1. Chemical composition and
physical properties of
plant viruses
N. H. SHANKAR REDDY
Ph.D., Plant Pathology
Annamalai University

2. Chemical composition
Nucleic acid (NA)
 The composition of NA ranges from 5 - 40 % (TMV – 5 %)
 Its contains RNA or DNA as genetic material, but never both
 Elongated viruses contain lower nucleic acid, whereas spherical
virus contain higher percentages of nucleic acid.
 NA is the infectious material of plant virus (Gierrer and Schramm,
1956)
 Weight of viral nucleic acid ranges from 1-3 million daltons
 Different methods are used to obtain nucleic acids, i.e. hot salt
method, phenol method, detergent method and alkaline method.

3. Protein coat (PC)
 The composition of protein ranges from 60 - 95 % (TMV – 95 %)
 The protein coat is called ‘capsid’, the structural subunits of capsids are called
‘capsomere’
 Protein coat only protects nucleic acid (NA) from unfavourable extracellular
environment and has no role in disease spread or transmission.
 It facilitates nucleic acid entry into the host cells and interacts with vector for specific
transmission.
 PAGE and western blotting are widely used to analyse viral proteins.

4. Virus NA content
(%)
Protein
content (%)
All viruses 5 - 40 60 – 95
TMV 5 95
Turnip yellow mosaic virus
(TYMV)
34 66
PVX 6 94
PVY 6 94
Cucumber mosaic virus (CMV) 18 82
tobacco ring spot virus (TRSV) 40 60

5. Physical properties of viruses
Thermal inactivation temperature (TIP)
 The temperature at which the infectivity of virus can be completely lost is called as
TIP.
 TIP may vary with viruses, TIP for the most of the viruses ranges from 55-70 o C,
whereas TMV requires 93o C.

6. Dilution end point (DEP)
 The lowest dilution at which sap from an infected plant is still infectious when
mechanically inoculated is known as DEP
 The DEP may vary with viruses and ranges from 10-1 to 10-7
 The DEP of TMV is 10-6, Carrot yellow mosaic virus is 10-4

7. Longevity in crude sap (LIV)
 The storage time after which the sap losses its infectivity is called as LIV. To
determine LIV the crude sap sample can be normally stored at 20o C
 In vitro longevity of infected sap of TMV is 3000 days, the purified virions
are remains viable for 50 years when kept at 5o C, whereas the longevity of
Nicotiana glutinosa is 102 h at 8-18o C

8. Local lesion assay
• A tool by which virus could be measured by showing that the amount of virus
present in the plant sap preparation is proportional to the number of lesions
produced on appropriate host plant leaves rubbed with the sap.
• A quantitative estimation of the infectivity of a preparation of a pathogen,
Eg - a suspension of bacteria or viruses, from the number of lesions
produced in inoculated leaves.

9. Video available at you tube
Channel – Geeky Researcher