Cultural taboos keep most humans from inbreeding, but plants
must rely on a complex internal warning system. In a new study,
scientists have teased apart how this botanic chastity belt
operates. As many commercial plant species have lost the ability
to guard against incest, the findings may help breeders
circumvent inbreeding to create more robust plants. Since the
early 20th century, scientists have known that many plants
reject their own pollen as well as that from close relatives.
Only in the 1980s did researchers find a class of enzymes in the
pistil, or female part of plants, that could destroy
"incompatible" pollen. If compatible pollen entered the flower,
the reasoning went, these enzymes, called S-RNases, were somehow
cleared away before they could do any damage. Now Bruce McClure,
a biochemist from the University of Missouri at Columbia, and
colleagues have upset this notion. When the researchers examined
compatible and incompatible pistil-pollen combinations in
tobacco plants, they found that S-RNas