Thidiazuron-induced hypertrophic growth from foliar disks of <Emphasis Type="Italic">Kalanchoe pinnata</Emphasis> leads to visualization of a bioactive auxin gradient across the leaf plane

Thidiazuron induces a variety of effects in foliar explants of K. pinnata cultured in vitro. Of these, the induction of an organized hypertrophic growth at the vein ending on the proximal side of leaf disks is a significant morphogenetic effect. This polarized hypertrophy is considered an exclusive auxin-mediated response, as the effect is completely reversed by auxin efflux inhibitor 2,3,5-triiodobenzoic acid. With the magnitude of hypertrophic growth from individual disks taken as a manifestation of putative auxin levels, the occurrence of a gross, decreasing bioactive auxin gradient from median-basal to peripheral locations across the leaf plane has been observed.