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If genetically unrelated (nonmatching) pollen lands on the stigma, the pollen germinates and produces a pollen tube that then runs through the plant's pistil and into the plant's ovaries. Fertilized eggs then develop into seed ready to be grown in a garden or a producer's field.

However, if "self-related" pollen lands on the stigma, the stigma's outer (epidermal) layer genetically recognizes the type of pollen and precipitates a self-incompatible reaction that inhibits the pollen tubes from growing. The Cornell group found that pollen recognition is based on highly specific lock-and-key interactions between receptors (the lock) on the stigma surface and ligands (the key) on the pollen surface. "If the pollen is matching kin, the receptor on the stigma is activated to prevent pollen tube growth," says Kachroo. "If the pollen is nonmatching, the receptor is not activated and pollen tubes can grow."

With this revelation, scientists are one step closer to understanding the reproductive barriers of flowering plants and their evolution. "The potential is to finally grasp -- at the molecular level -- which genes are needed for pollen rejection," says Mikhail Nasrallah. "The ability to silence, mutate and transfer the genes that control the self-incompatibility barrier could be a boon to breeders. Even self-fertilizing crops like tomatoes and rice can benefit from increased genetic variability."

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Contact: Blaine P. Friedlander Jr.
bpf2@cornell.edu
607-255-3290
Cornell University News Service
6-Sep-2001