Immunity
ated with the plant’s reaction to pathogens. It is a kind of
suicide reaction by the plant initiated in order to kill or
limit the threat of the pathogen that is attempting to invade
the plant—and is one of the most fascinating aspects of the
plant immune system. You might have seen whole branches
of a tomato plant curl up and die shortly after a bite from
an insect—the concept is to burn the bridges in front of
the invading pathogen in order to save the plant as a whole.
This process spreads rapidly and is often quite effective. For
gardeners tending plants exhibiting this reaction, the plant
should be stripped back to the stem or branch just before
the dying portion in order to help minimize the amount of
‘HR’ that will occur and the pathogens that might invade.
Other plant reactions are also initiated as a result of ‘HR.’
Local and systemic-acquired resistance is often found very
near the site of pathogen attack—or sometimes quite some
distance away, indicating the key role of these forms of
resistance in the plant. Many studies have examined these
plant responses and the results clearly indicate the complexity of the regulation of these responses within the
plant and the interplay of the signals between
the pathogen, the environment and the
host plant itself. The hypersensitive
cell-death response is one of the most
powerful mechanisms the plant has to
defend itself and as gardeners we need
to be able to recognize this response as
being something different from plant
failure. Some pathogens—such as those
“The hypersensitive cell-death
response is one of the most
powerful mechanisms the
plant has to defend itself.”
carried by an insect—are not transferable in themselves
to other plants and therefore the entire plant need not be
removed. It is the insect itself in this case that spreads the
disease to other plants.
Another very interesting method of plant self-defense is
when they ‘tag’ an invading insect with a protein. When
digested by the attacking insect this tagging protein converts
to another chemical within the insect, a chemical that will
then be recognized by a plant when the insect is feeding
from it. The chemical gives off a sort of SOS to the other
plants to alert them that this particular insect is a bad guy.
They then immediately begin to put into force their defense
systems, which will repel the insect before it has had much
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Maximum Yield USA | March 2012