When plant breeders want to re-generate plants that are virus-free using asexual multiplication (in order to obtain clones of the primary unhealthy plant), they often collect the apical meristem from the infected plant, and cultivate it in appropriate media, so that a new, complete and virus-free plantlets develop. The fact that viruses spread systematically in the whole plant except the meristems when they colonize a new plant host, via phloem vascular element, is well known. But nothing is said about the putative molecular and cellular mechanisms that allow the pluripotent cells of the meristems to stay uninfected. Do you have some clues about this issue, or does this still remain a complete mystery of plant virology?
In the meristem there is no cells differentiation. Virus can't move from cell to cell through plasmodesmesta using their Movement protein.
according to me, I think that the phloem is not enough developped in the meristem, so that the virus can't spread very quickly at the meristem. Another hypothesis, there is a very intense metabolic activity in the meristem
In the meristem there is no cells differentiation. Virus can't move from cell to cell through plasmodesmesta using their Movement protein.
no vascular system in meristem is available for virus movement, viral replication (viral inactivating system) cannot cope with faster meristem cell division and auxin level might also limit viruses.
Apical meristem are actively diving cells they dont have well established vascular system like old tissues do. I suppose that these actively dividing cell maybe secreating some sort of chemical( plant hormones) that keep away viruses and bacteria from entering or surviving. I also think maybe its due to high metabolic activity and high level of chemicals( high concentration) which is too much for microorganism to coop with.
Dear Hervé!
I think even when you do tissue culture, using meristems there is no guarantee that all plants will be free of viruses. You'll get some free plants viruses and another infected. You should test samples from plants produced from each meristem to see if they are actually virus free. Thus, also in the early stages of laboratory is important to keep plants produced from each meristem identified and separated until have the results of the testing of virus. The efficiency of the elimination of virus will depend on the size of the meristem used, the ability of the technician to remove the meristem and which viruses were present in the plant.
Three main reasons-
* High metabolic processes(Enzymes activity)
*High concentration of auxin and Cytokinin hormone (Low pH)
*Cell multiplication very high and Plamodesmata size very small which prevent the movement of the virus from one cell to another cell.
Dear Hervè!
A recent paper about this topic:
Citrus leaf blotch virus invades meristematic regions in Nicotiana benthamiana and citrus
JESÚS AGÜERO, MARÍA CARMEN VIVES, KARELIA VELÁZQUEZ, SUSANA RUIZ-RUIZ†,
JOSE JUÁREZ, LUIS NAVARRO, PEDRO MORENO AND JOSÉ GUERRI*
MOLECULAR PLANT PATHOLOGY (2013) 14(6), 610–616
Sincerely yours,
Paulo
Dear all,
probably something to see with silencing (again!).
Some papers going in this direction:
http://www.ncbi.nlm.nih.gov/pubmed/16040651
http://www.ncbi.nlm.nih.gov/pubmed/20015979
Best wishes
Franck
on newly growing meristem, there is high rate of cell divition, so it is a result of virus free cell duplication
Meristematic cells are considered as virus free because:
1). Meristematic cells have high multiplication rate than viral cell multiplication rates.
2). Viruses generally move in plant body through vascular bundles. There is the absence of vascular bundles in meristematic regions.
3). High auxin concentration and cytokinin concentration and low pH value at which viruses could not survive.
4). High metabolic activity.
5). RNA silencing mechanism. According to some findings, it has been hypothesized that the defense systems in meristematic regions treat viruses as foreign particles thus prevent the viruses into the meristematic regions.
The viruses are associated with the vascular system of the plants. In the newly developed meristem as the the growth is very fast, the vascular tissues are not yet developed. As the virus moves via vascular tissues, so it can not reach the apical meristem.
Fast cell multiplication in apical meristem region faster than virus multiplication is another reason of less virus presence.
Thank you Potshangbam for this new contribution. Can you please give references for your affirmation? I found it surprising since I believe viruses are usually described as very fast replicating compared to eucaryotic cells!
a recent publication on this topic :
Mystery solved: How do tips of plants stay virus-free?
https://globalplantcouncil.org/mystery-solved-how-do-tips-of-plants-stay-virus-free/
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