Tobacco Mosaic Virus TMV (History + Symptoms + Structure + Life Cycle)
Tobacco Mosaic Virus Symptoms, Structure and Life Cycle of TMV, Mosaics Definition
Tobacco mosaic virus also known as TMV is the most extensively studied virus in plants. It was discovered by Iwanowski (1892) and obtained in pure state by Stanley (1935). It has a helical symmetry. TMV is a cylindrical structure with a molecular weight of 40 million and 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 done at various stages of solubility properties, dissociation with including the studies of RNA component and separate protein. These studies have yielded the extravagantly thorough and exact structure of the virus particle.
TMV Symptoms – Mosaics Definition
Tobacco Mosaic Virus Symptoms: The TMV virus/viruses 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 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 plant to many degrees remains stunted. The disease is characterized by mottling of leaves referred to as ‘mosaics’.
Tobacco Mosaic Virus Structure: The virus has a coat made up of protein which consists of 2130 identical protein sub-units. Each of these sub-units have a molecular weight of 18,000. The sub-unit is composed of a singular chain of 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 RNA strand has a radius of 40 A° which is embedded into the helix with the radius 85 A° of identical pitch of 23 A° that is further formed by the protein sub-units. 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 special staining technique with phosphotungst 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 inclusion body. The TMV with having a crystalline inclusion body also known to have true virus particles.
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 heating up to 90°C for 10 carry the virus on his hands to healthy plants.