| MadSci Network: Botany |
"Cancers" in plants are called galls. Crown gall disease is probably the most well known. As you state in your question, the bacterium Agrobacterium tumefaciens causes the disease.
The microbe carries a plasmid (called Ti). This plasmid enters the infected cell and carries genes which become inserted in the plant's genome. The genes lead to uncontrolled growth of the plant cell, and also cause it to produce and secrete compounds called opines which the bacteria use as a source of food. In essence, the bacteria create "plant cancers" so they can eat! A related species, Agrobacterium rhizogenes causes the development of galls consisting of roots (even if present on the stem of the plant).
Some species of wasps lay their eggs in plant tissues. The larvae secrete chemicals which cause galls to develop. The larvae complete their development inside the gall.
Your student may also wish to look up something called a witch's broom which is most commonly noted in pines (at least all ones I have seen have been in pines..). The "broom" represents a disorganization of branches and needles in the tree, and can be associated with genetic rearrangements.
-L. Bry, MadSci Admin
References: Genetics of Bacterial Diversity, D.A. Hopwood, 1989
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