Plant immune systems
Date: Around 1993
Do plants have an immune system? How does it work? Are plants
able to "fight off" infections such as Dutch Elm disease?
In the broadest sense, an immune system is any method an organism
has protect itself from succeeding to another organism's efforts to undermine
its health and integrity. In this sense, yes, plants have immune systems.
Plants do NOT have "active" immune systems, like humans, including
macrophages, lymls, antibodies, complements, interferon, etc., which help us
ward off infection. Rather, plants have "passive" mechanisms of protection.
For instance, the waxy secretion of some plants (cuticle) functions to help
hold in moisture and keep out microorganisms. Plants can also secrete
irritating juices that prevent insects and animals from eating it. The thick
bark of woody plants is another example of a defensive adaptation, that
protects the more delicate tissues inside. The chemical secretions of some
plants are downright poisonous to many organisms, which greatly enhance the
chances of survival for the plant. Fruits of plants contain large amounts of
vitamin C and bioflavonoids, compounds which have been shown in the lab to be
anti-bacterial and antiviral. So in these ways, plants can improve their
chances of survival. Hundreds of viruses and bacteria attack plants each
year, and the cost to agriculture is enormous. I would venture to guess that
once an organism establishes an infection in a plant, the plant will not be
able to "fight" it. However, exposure to the sun's UV light may help control
an infection, possibly even defeat it, but the plant does not have any
inherent "active" way to fight the infection.
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Update: June 2012