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Tobacco mosaic virus is also known as TMV is the most extensively studied virus in plants. It was discovered by Iwanowski (1892) and obtained in a pure state by Stanley (1935). It has helical symmetry.
Tobacco Mosaic Virus Structure
TMV is a cylindrical structure with a molecular weight of 40 million and a dimension of 160 x 3000 A°. Through X-ray diffraction and electron microscopy, various extensive studies have been done.
Not only this, these studies have been done at various stages of solubility properties, and dissociation including the studies of RNA components and separate proteins.
These studies have yielded the extravagantly thorough and exact structure of the virus particle.
Detailed TMV Structure
The virus has a coat made up of protein which consists of 2130 identical protein subunits. Each of these sub-units has a molecular weight of 18,000.
The sub-unit is composed of a singular chain of a known sequence of 158 amino acids. An ellipsoid with an axial rotation of 3:1 is produced by the folding of the chain. The virus has a single strand of RNA. It has a 2.4 million molecular weight with 6500 nucleotides.
The helix formed by the RNA strand has a radius of 40 A° which is embedded into the helix with a radius of 85 A° of the identical pitch of 23 A° that is further formed by the protein subunits.
Tobacco Mosaic Virus Diagram
Down the middle of the molecule runs a cylindrical hole with a radius of 20 A° that can be seen in the electron microscope if a special staining technique with phosphotungstic is used.
The rod is elongated and twists to form a uniform spiral structure just like a hollow rod with a central core of RNA. A protein sheath surrounds this RNA core.
Under appropriate conditions, the viral particles induce the formation of a crystalline structure known as an inclusion body. The TMV with having a crystalline inclusion body also known to have true virus particles.
Tobacco Mosaic Virus Symptoms
The TMV virus attack is confirmed when on the younger leaves of tobacco plants, the veins may show a clear ring, which is later on followed by mottling.
With the enlargement of leaves, dark green spots of abnormal size appear, and at a later stage, they transformed into crumpled blister areas which are irregular.
On the other hand, the remaining portion of tissue becomes more chlorotic with the passage of time. Also, the growth of plants to many degrees remains stunted.
The disease is characterized by the mottling of leaves referred to as ‘mosaics’.
Tobacco Mosaic Virus Life Cycle
Well, in the extracted host plant juice, the TMV remains active up to a time limit of 25 years. It is infectious in dilutions up to 1: 1,000,000 and withstands heat up to 90°C for 10 carry the virus on his hands to healthy plants.