The structural requirements of flavonols that induce pollen germination of conditionally male fertile Petunia (original) (raw)

Abstraet--Flavonols are essential for pollen germination and sustained tube growth in Petunia hybrida. An in vitro bioassay, based on biochemical complementation of flavonol-deficient pollen, was used to compare how modifications at different sites on the basic flavonol molecule affect the efficiency of pollen germination. This structural-activity analysis using methylated or glycosylated derivatives showed that only flavonols with unsubstituted hydroxyl groups at positions 3 and 7 could induce rapid pollen germination. In addition, the enhanced germination frequency associated with a hydroxyl group at position 5 was abolished by substituting a methyl group. Increased hydroxylation of the flavonol B-ring had an inhibitory effect on germination, but methylation of the same hydroxyl groups promoted germination. Additional hydroxyl groups within the A-ring at carbon 6 had a mixed effect, but a methoxyl group at position 6 enhanced germination in all cases. Substitutions at position 8 were somewhat inhibitory and introduction of an isoprenyl group into ring A was toxic to both mutant and wild type pollen.