[27]

FLAVONOIDS REGULATE AUXIN TRANSPORT DURING GRAVITY RESPONSE IN ARABIDOPSIS Avery McGuire, Aaron M. Rashotte, and Gloria K. Muday Department of Biology, Wake Forest University, Winston-Salem, North Carolina, 27109

     Flavonoids have been implicated in the regulation of polar auxin transport in Arabidopsis.  One class of flavonoids, the aglycone flavonols, is believed to be central in regulation of auxin transport.  Arabidopsis plants with the tt4 (2YY6) mutation in the gene encoding the first enzyme in flavonoid biosynthesis, chalcone synthase, make no flavonoids.  This tt4 (2YY6) mutant has elevated auxin transport consistent with the absence of an endogenous inhibitor of transport.   In a recent series of studies, the gravitational responses of tt4 (2YY6) seedlings were examined and compared with wild-type seedlings.  Roots of tt4 (2YY6) plants showed both a distinct lag in initiation of gravitropic bending and have a much slower rate of bending in response to gravity.  These investigations will be extended to include examination of the effect of the tt4 (2YY6) mutation on hypocotyl gravitropism and phototropism.  Additionally, the effect of gravity stimulation on the location and concentration of flavonoids will be examined with a dye that becomes florescent in response to binding flavonoids.  Expression of auxin-responsive promoter constructs will also be examined in relationship to the changes in flavonoid localization.  As a whole, these experiments should provide insight into how flavonoids act to control auxin transport during gravitropic bending and when and why the absence of flavonoid.