Polyamines, auxins and organogenesis in leafy spurge (Euphorbia esula L.)

Canaline and canavanine (inhibitors of polyamine biosynthesis) effects on root and shoot formation were determined in vitro for etiolated hypocotyl segments of leafy spurge (Euphorbia esula L.). Canaline (an ornithine analogue) at 10 to 100 μmol/L inhibited root and shoot formation. The simultaneous application of putrescine did not reverse canaline-induced inhibition of root formation. Ornithine, a precursor of putrescine via the ornithine decarboxylase pathway, unexpectedly inhibited root formation. Canavanine (an arginine analogue) at 30 to 100 μmol/L inhibited root and/or shoot formation. Inhibition of root formation by canavanine was not reversed by agmatine or putrescine, but was partially reversed by arginine. Indoleacetic acid (IAA) inhibited shoot formation, stimulated root formation, and partially reversed the inhibition of root formation by either canaline or canavanine. IAA generally increased endogenous levels of free polyamines in controls and canalineor canavanine-treated tissues, but these changes were small and probably had little effect on organogenesis. IAA also partially reversed the inhibition of root (but not shoot) formation by arcaine and pentamidine, inhibitors of polyamine action in mammals. The roles of the polyamines in plants is not clear, but the polyamines may play only minor roles in root and shoot formation.