Inhibition by 2,4-D of somatic embryogenesis in carrot as explored by its 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 that difluoromethylornithine (DFMO) can counteract this inhibition has been 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 glutathione), ethanol/acetaldehyde and abscisic acid was not counteracted by DFMO, indicating that the inhibitory effect of 2,4-D is not manifest through the formation of these compounds. Embryogenesis was abolished by micromolar concentrations of the polar auxin transport inhibitors 2, 3, 5-triiodobenzoic acid (TIBA), N-1-naphthylphthalamic acid (NPA) and 9-hydroxyfluorene-9-carboxylic acid (HFCA). This inhibition was counteracted to a considerable extent by DFMO. Inhibition by relatively high concentrations of the antiauxin 2-(p-chlorophenoxy)-isobutyric acid (CPIB), which does not affect polar auxin transport, was in contrast not counteracted by DFMO. These findings indicate that exogenous auxins may inhibit embryogenesis by interfering with the ability of postglobular embryos to set up internal auxin gradients necessary for polarized growth.
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Nissen, P., Minocha, S. Inhibition by 2,4-D of somatic embryogenesis in carrot as explored by its reversal by difluoromethylornithine. Physiologia Plantarum. December, 1993;89(4):673-680. doi: 10.1111/j.1399-3054.1993.tb05272.x