Plant Growth Regulators - 8 • In addition, auxins: • Promote other hormone production, especially ethylene, when auxin concentration changes • Promote flower initiation • Reduced auxin initiates leaf abscission by promoting ethylene synthesis • Fruit development requires auxin produced by the developing seed. Auxin pastes applied to developing ovaries can promote parthenocarpy (fruit development in the absence of viable seeds). Parthenocarpy is also induced by abscisic acid. Normal Fruit No fruit with seeds removed One row of seeds removed Auxins are toxic in large concentrations. These concentrations affect mostly eudicots but not monocots. Monocots seem to be able to rapidly degrade the synthetic auxins. Synthetic auxin herbicides include 2-4-D and 2-4-5-T. (Agent orange of the Vietnam era contained synthetic auxins.) • Used as defoliants • Used as weed killers While "poorly" documented, adverse effects on humans are also asserted from the use of synthetic auxins in high concentrations. Cytokinins
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