Some of the Most Important Properties of Plant Viruses are as follows:
Properties of various plant viruses have been studied in detail. Since the development of virology (science of viruses), tobacco mosaic virus has been the main source for investigations, and most of the virus properties described below are based on it.
1. Viruses are highly infectious. Bawden working on tobacco mosaic virus found it to be infectious even in 1/1,000,000 dilution.
2. Viruses are highly resistant to acids, alkalies and salts. Tobacco mosaic virus is affected by hydrochloric and nitric acids only when 1 gm. of acid is added to 100 c.c. virus solution. They are more affected by alkalies, such as sodium hydroxide and sodium carbonate. Salts like sodium chloride, silver nitrate, and mercuric chloride however do not affect them much, 1 gm copper sulphate in 100 c.c. virus solution, and 4% formaldehyde solution destroy tobacco mosaic virus completely. According to Vinson, acetone and alcohol have no effect on viruses at low temperatures.
3. Viruses are resistant to high temperatures. Tobacco mosaic virus can infect healthy plant even after being kept at 80°C for two days. However, it loses its power of infection within 10 minutes at 85°C-90°C temperatures.
4. Direct sunlight has no effect on viruses. Tobacco mosaic virus is not affected by X-rays and mercury vapours, till the exposures do not exceed half an hour and one hour respectively.
5. Viruses can be filtered through Brefeld and Chamberlain filters, but according to Mulvania, they can be filtered through collodian membrane also.
6. Viruses can retain the power of infection for long periods, even out of the living cells. Tobacco mosaic virus retains its infectivity in extracted cell sap for 5 years (Dickson, 1925) and according to Valleau and Johns, it remains infectious in dried tobacco leaves for 31 years.
7. Vinson and Petre precipitated viruses with the solution of safranin solution, acetone and ethyl alcohol. The precipitate obtained by safranin solution, has no power of infection but it regains it when ethyl alcohol added to the precipitate.
8. When the cell-sap contaminated with virus is subjected to a high speed centrifuge, viruses get sedimented like proteins.
9. Viruses increase in number and size within the living protoplasm of cell.
10. They can be transmitted from infected plant to a healthy plant by mechanical and biological means.
11. Insects which transmit viruses are known as vectors. A particular virus can be transmitted only by a particular species of insect and on a definite species of host. This sort of selection of the vector and the host is known as physiologic specialization.
The general properties described above are more or less common and the differences are of degree only.