Another interesting features is that plant viruses do not generally replicate in the cells into which they are injected. Rather, they become systematically distributed throughout the the plant through the fine pores(plasmodesmata) in the cell walls, and also possible through the phloem.
Our information concerning replication of plants viruses is based mostly upon the work done in Tobacco mosaic virus.
Life cycle of Tobacco Mosaic Virus:
Tobacco mosaic viruses are single stranded RNA viruses.
Following entry into a host cell, the uncoating of the virion occurs. The plant cells are structurally more complex than bacteria and the enzymes involved in RNA replication and transcription are confined to the nucleus. The uncoated viral RNA gains access to the nucleus of the host and induces to form an enzyme called RNA-dependent RNA polymerase. This enzyme utilizes the viral RNA as a template and forms complementary RNA. This complimentary copy of RNA, called-strand(antisense-strand), serves as a template to produce more virus+strands. The +strands may serve as mRNA for translation of capsid proteins. The coat protein molecules are synthesized either in the cytoplasmin vicinity of nucleus or in nucleus. The coat protein molecule are synthesized either in the cytoplasm in vicinity of nucleus or in nucleus. The coat protein molecules aggregate around the RNA molecules and the mature virions are produced.
Normally, cell lysis does not occur and the progeny TMV particles are released from the cell, possibly owing to the mechanical damage.
Satellite Plant Viruses
Sometimes, one virus depends upon another virus for its proper replication in a host cell. Such a situation is known as satellism and the virus that is dependent on another virus is called a satellite virus. The term 'activator' is applied to the virus that helps the satellite virus to successfully infect and replicate in the host cell and the phenomenon is called activation. The first satellite virus(SV) to be recorded was found in association with tobacco necrosis virus, which measures about thirty nm in diameter, often occurs quite independently in roots of tobacco, and is able to replicate normally. Sometimes, both tobacco necrosis virus and the small satellite virus occur together in the roots of the host plant. Satellite virus in contrast is unable to multiply in the host cell and depends upon the assistance of tobacco necrosis virus for its own replication.