Pollination- or Wound-Induced Kaempferol Accumulation in Petunia Stigmas Enhances Seed Production

Flavonols are essential for pollen germination and tube growth in petunia and can be supplied by either the pollen or stigma at pollination. HPLC analysis and a sensitive bioassay demonstrated that both pollination and wounding induce flavonol accumulation, especially kaempferol, in the outer cell layers and exudate of the stigma. Pollination and wounding induced nearly identical flavonol kinetics and patterns of accumulation in the same target tissue, suggesting that they share elements of a common signal transduction pathway. The wound response was systemic, because kaempferol accumulated in the stigma when distal tissues, such as the corolla, stamens, or sepals, were wounded. We have exploited the germination requirement for flavonols and the high level of kaempferol that accumulates after wounding to enhance plant fecundity. Seed set was significantly increased by mechanically wounding the corolla and stamens prior to the application of pollen to the stigma. A reproductive role for a plant secondary metabolite and the specific function of stigmatic kaempferol are discussed from an evolutionary perspective.