Ask A Scientist© Biology Archive

Author:      stephanie
Text:        Do plants have an immune system?  How does it work?  Are plants 
able to "fight off" infections such as Dutch Elm disease?

Response #:  1 of 1
Author:      wizkid
Text:        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.