Name: Sharon H.
Why is it that when a very small virus infects a plant cell by crossing its
membrane, the virus spreads rapidly throughout the entire plant without crossing additional
Plant cells have cell walls too besides cell membranes.
Anthony Brach, Ph.D
The question 'why' is simple to answer: in order to increase the chance that virus
offspring will reach their next victim (or host, as we say). If virus particles were
confounded to the one cell originally infected, they would never make it to the next
plant. Think about it, would that be a success-story in biology? Would it not be required
to pass on to neighbour cells, and then to neighbour plants, in order to survive? You
probably also want to know how. The question 'how' is often more interesting, and also
more difficult than 'why' (the latter is more phylosophical). Viruses have special
strategies to spread through their host, or, more importantly (but with the same intend)
from host to host. For instance, the common cold virus makes you sneeze, to increase the
chance it is leaving the body in droplets, that are then inhaled by the next patient-to-be.
Since plants do not sneeze, plant viruses depend on insects
to be transferred from one plant to another (plant viruses also are more commonly
transferred vertically, that is, from mother to daughter plant, than animal viruses are).
So they must spread to the edible parts of the plant. They can do this via the plant sap,
by actively passing plant cell membranes. I am not sure that is not possible but it will
depend on the type of virus.
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Update: June 2012