INHIBITION BY 2,4-D OF SOMATIC EMBRYOGENESIS IN CARROT AS EXPLORED BYITS REVERSAL BY DIFLUOROMETHYLORNITHINE

The development of somatic embryos is, in many plants, inhibited by 2, 4-dichlorophenoxyacetic acid (2,4-D) and other auxins. The finding tha t difluoromethylornithine (DFMO) can counteract this inhibition has be en used to test some of the hypotheses for the mechanism of inhibition . Inhibition of somatic embryogenesis in carrot (Daucus carota L.) by exogenous ethylene (from ethephon), antioxidants (ascorbic acid and gl utathione), ethanol/acetaldehyde and abscisic acid was not counteracte d by DFMO, indicating that the inhibitory effect of 2,4-D is not manif est through the formation of these compounds. Embryogenesis was abolis hed by micromolar concentrations of the polar auxin transport inhibito rs 2, 3, 5-triiodobenzoic acid (TIBA), N-1-naphthylphthalamic acid (NP A) and 9-hydroxyfluorene-9-carboxylic acid (HFCA). This inhibition was counteracted to a considerable extent by DFMO. Inhibition by relative ly high concentrations of the antiauxin 2-(p-chlorophenoxy)-isobutyric acid (CPIB), which does not affect polar auxin transport, was in cont rast not counteracted by DFMO. These findings indicate that exogenous auxins may inhibit embryogenesis by interfering with the ability of po stglobular embryos to set up internal auxin gradients necessary for po larized growth.