1. The redistribution of auxin during gravitropism in maize roots

2. Developmental effects of auxin ¤ Regulate apical dominance ¤ Promote lateral and adventitious root formation – even though auxin inhibit the primary root elongation ¤ Delay the onset of leaf abscission ¤ Regulate the floral bud development ¤ Promote fruit development ¤ Induce vascular differentiation

3. Developmental effects of auxin ¤ Regulate apical dominance ¤ Promote lateral and adventitious root formation – even though auxin inhibit the primary root elongation ¤ Delay the onset of leaf abscission ¤ Regulate the floral bud development ¤ Promote fruit development ¤ Induce vascular differentiation

4. Regulate apical dominance – apical bud inhibits the growth lateral buds + TIBA (efflux inhibitor) in lanolin placed below the shoot apex  Axillary bud formation Direct-inhibition model  Auxin is synthesized in the shoot apex and is transported basipetally to the axillary buds ( [auxin] gradient)  axillary buds are more sensitive to auxin than other shoot tissues + IAA inhibits the growth of lateral buds

5. However ¤ After decapitation 4 h, the level of IAA is 5-fold increase ¤ Applied auxin directly to terminal bud, [auxin] shoot , axillary bud outgrowth ¤ radiolabeled auxin does not enter basipetal the bud ¤ axr1 mutant (unable to respond to auxin), much branching phenotype ¤ Transgenic plant (02): auxin-responsive promoter + luciferase (LUX) gene decapitated  the expression of LUX increase in and around the axillary buds ¤ After decapitation, an increase in cytokinin imported from root via xylem, Add cytokinin in axillary buds  bud growth (but bud growth prior to the increase of cytokinin) ¤ After decapitation, ABA level decrease, in some species. ¤ Carotenoid cleavage product ¤ Grafting studies Root signals interact with auxin in the xylem  ongoing research Web Essay 19.4

6. Auxin induce vascular differentiation – is polar and occurs from leaves to roots Auxin  Cytokinin  Xylem and phloem differentiation: high auxin conc. Only phloem differentiation: low auxin conc.

7. Auxin promote fruit development produce auxin

8. The commercial uses of synthetic auxins ¤ prevention of fruit and leaf drop ¤ promotion of flowering ¤ induction of parthenocarpic fruits – seedless fruits ¤ thinning of fruit ¤ rooting of cutting ¤ herbicide for dicot weeds