TRANSPORT OF IAA AND ACC IN FLORAL ORGANS OF IPOMOEA-NIL (CONVOLVULACEAE)

The involvement of the stamens as transporters of plant growth regulators in flowers was examined by measuring the movement of C-14-indole-3-acetic acid (IAA) and C-14-1-aminocyclopropane-1-carboxylic acid (ACC) through floral organs of Ipomoea nil. During the transport of C-14-IAA through isolated filament segments, the polar accumulation of C-14-IAA in receiver blocks increased with time during filament development, which correlated with polar efflux rates at older stages of filament development. An inhibitor of polar IAA transport, 2,3,5-triiodobenzoic acid, disrupted the polarity of auxin transport by reducing the movement of C-14-IAA from filaments into receiver blocks. Transport of both C-14-IAA and C-14-ACC through filaments into other floral organs also was monitored in isolated flower buds in the laboratory and intact buds in the greenhouse. In isolated and intact buds 21 hr before anthesis, substantially higher levels of isotope were recovered in corolla tissue when C-14-ACC was transported through the filaments than when C-14-IAA was transported from the filaments. In isolated buds, substantial levels of both isotopes accumulated in the pistil (69 hr and 45 hr before anthesis), but minimal amounts were observed in receptacle and calyx tissues (69 hr to 21 hr before anthesis). In intact buds, high levels of both isotopes were recovered in receptacle, calyx, and pistil tissues (69 hr to 21 hr before anthesis). The results from this study support the hypothesis that Ipomoea stamens are transporters for ACC and IAA to regulate ethylene production in the corolla and other floral tissues.