Distribution and Metabolism of IAA in Relation to the Growth of Helianthus Hypocotyls

Abstract

A 2-μl droplet of 3H-IAA was applied to the apical cut surface of hypocotyl sections of light-grown Helianthus seedlings. Dark and morphactin pretreatments caused significant but opposite effects on diffusible auxin levels, even though both enhanced hypocotyl elongation. Dark treatment increased the amount of diffusible auxin, while there was no detectable IAA in the diffusates from morphactin-treated plants. In dark-treated plants, total peroxidase activity was reduced, although the pattern of isoenzymes was the same as in controls and morphactin-treated plants. The results indicate that auxin transport is not necessary for maintaining elongation.