Petunias show that the mechanisms behind inbreeding prevention are similar to immune response. This diagram shows non-self pollen fertilizing a petunia and, conversely, self-pollen perishing. The female part of the petunia flower secretes an enzyme that is designed to deter pollen tube growth, thereby preventing fertilization. However, in the cases that the pollen has come from a genetically different plant, the pollen produces its own protein that combats the pistil's enzyme. With the enzyme out of the way, the pollen tube can keep growing and fertilization can occur. To learn more, see the NSF news release.

Credit: Zina Deretsky, National Science Foundation