Tobacco Mosaic Virus (TMV)

Classification

Tobacco Mosaic Virus (TMV)

It is an RNA virus that infects members of the Solanaceae family of the plant kingdom – its main host plant is the tobacco plant. The main symptoms of this disease are the mottling of the leaves, i.e. spots or patches on them. Due to the destruction of chlorophyll in the leaves, discoloration begins. Yellow spots first appear on new leaves, after which mottling becomes clearly visible. On mature leaves of tobacco, deep greenish-yellow, chlorotic irregular spots (mosaic) appear and the growth of the plant stops.

The disease in tobacco plants was known since the end of the nineteenth century and in 1883 a scientist named Adolf Meyer reported that this disease spreads from one infected plant to another in the same way as other bacterial diseases. In 1892 Ivanovsky discovered this virus while Rosalind Franklin worked on its crystallization but his experiments proved futile.

After his death, Stanley (1936) completed its crystallization. In 1958, Stanley presented the model of this virus.

virus has a rod-like structure. After crystallization, these viruses look like fine needles. The virus is rod-like, about 300 nm long and 18 nm in diameter. The electron graph obtained by negative staining technique makes it clear that in the center of the virus particle there is a stranded RNA molecule of about 4 nm diameter. Surrounding it, a protein coat is found on the outside, which is called capsid. The genomic RNA is 6890 nucleotides long, whose molecular weight is about 4 lakhs. All the genetic signals for the formation of virus particles are found in the nucleic acid of TMV. With these signals, viral RNA is replicated in the host cell and the coat protein is synthesized.

The RNA molecule remains coiled inside the protein coat, twisting like a hairpin. The protein coat is made up of 2130 subunits (capsomeres) which get together and wrap around the RNA in the form of a ring and form a rod-like shell. These subunits remain wrapped around this shell and form a rod-like shell. This shell has about 130 rings. Each ring cycle contains 16.3 protein subunits (capsomeres). These amino acids are arranged in four alpha-telics. The weight of each protein subunit is 17500. The molecular weight of each TMV particle is 40 million. From the chemical structure point of view, 94.4 percent protein and 5.6 percent nucleic acid are found in TMV.

Multiplication of Tobacco Mosaic Virus (TMV) This virus enters the plants through the cuts and infects them. The infection usually spreads from the plant sap of the diseased plant to the healthy plants. On reaching the host cells, the virus particles break down into protein and RNA. Using the enzymes and other genetic material and machinery of the host cell, the RNA is repeatedly multiplied and viral protein is synthesized, after which capsomere units are formed. Capsomeres and RNA get organized and form many tobacco mosaic virus particles. These virus particles are transmitted in the fields through air, water and transportation methods.

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