CHALCONE SYNTHASE AND FLAVONOL ACCUMULATION IN STIGMAS AND ANTHERS OFPETUNIA-HYBRIDA

Flavonol aglycones are required for pollen germination in petunia (Pet unia hybrida L.). Mutant plants lacking chalcone synthase (CHS), which catalyzes the first committed step in flavonoid synthesis, do not acc umulate flavonols and are self-sterile. The mutant pollen can be induc ed to germinate by supplementing it with kaempferol, a flavonol aglyco ne, either at the time of pollination or by addition to an in vitro ge rmination system. Biochemical complementation occurs naturally when th e mutant, flavonol-deficient pollen is crossed to wild-type, flavonoid -producing stigmas. We found that successful pollination depends on st igma maturity, indicating that flavonol aglycone accumulation may be d evelopmentally regulated. Quantitative immunoblotting, in vitro and in vivo pollen-germination, and high-performance liquid chromatographic analyses of stigma and anther extracts were used to determine the rela tionship between CHS levels and flavonol aglycone accumulation in deve loping petunia flowers. Although substantial levels of CHS were measur ed, we detected no flavonol aglycones in wild-type stigma or anther ex tracts. Instead, the occurrence of a conjugated form (flavonol glycosi de) suggests that a mechanism may operate to convert glycosides to the active aglycone form.