In flowering plants, reproduction is initiated when the pollen (the male) reaches the pistil (the female). For successful fertilization, the pollen must germinate and form a tube that grows within the pistil in order to reach the ovule. As the pollen tube extends, molecular information is exchanged that determines the compatibility of the pollen and pistil, such as their degree of genetic relatedness. In some plants, a toxin called S-RNase poisons the pollen tube if the pollen and pistil are too closely related, thus preventing inbreeding. Recent studies by Bruce McClure suggest the toxin is sequestered until the compatibility decision is made.

Credit: Nicolle Rager Fuller, National Science Foundation

This photomicrogaph shows a pollen tube (light blue) growing through the cells of a pistil. A toxin, S-RNase (dark blue), poisons the pollen to prevent plant inbreeding when necessary.

Credit: Ariel Goldraij, Mayandi Sivaguru, and Bruce McClure, University of Missouri-Columbia