1. Plants don’t have hormones do they?? Tropisms and polarity Clearly plant growth and development would not be possible without efficient communication among cells, tissues and organs. I hadn’t thought about that!

2. Phototropism Gravitropism Fruit ripening Embryo development

3. DR5::GUS reporter gene for auxin light Taiz/Zeiger, 2002 Lateral IAA movement increased IAA causes bending

4. Leaf development Apical dominance Lateral root development Vascular differentiation

5. Auxin transport and plant polarity

6. Avena coleoptile system

7. Classical auxin experiments

9. Indole-3-acetic acid (IAA) So that is what auxin looks like!! What was the material diffusing from Went’s agar block?

10. Went agar diffusion experiment

11. Auxin biosynthesis IAA

12. Taiz & Zeiger, 2002 control IAA Cell wall elongation assay of hypocotyl segments IAA induces an increase in the elasticity of the cell wall by reducing its pH. This allows the cells to expand easier

13. Figure 19.23 Kinetics of auxin-induced elongation and cell wall acidification in maize coleoptiles

14. Acid growth hypothesis  Acidic buffers induce cell elongation without auxin  neutral buffers inhibit auxin-induced cell elongation  inhibitors of H + -ATPase inhibit auxin-induced cell elongation ?

15. How could the acid growth hypothesis work?? auxin control ? ? ?

16. Cell wall structure Non-ordered wall structure Paralell ordered wall structure

17. Auxin and root gravitropism

19. Figure 19.31 Microsurgery experiments showed that the root cap supplies a root growth inhibitor

20. DR5-GFP in gravistimulated root DR5-GFP in gravistimulated root tips + 1µM NAA

21. Figure 19.29 pH changes in columella cells are involved in gravitropic signal transduction (B)

22. Root gravitropism

23. How to create cell polarity

24. How to NOT create cell polarity

25. Auxin importer AUX1 transports IAA and 2,4-D 1-NAA diffuses into the cell 1-NAA control

26. Polar auxin transport (basipetal) in stems AUX1 ABCB4 ABCB1/19 PIN1 anionic IAA - Undissociated IAAH

27. Polar auxin transport and the chemiosmotic model Influx: 1. Passive diffusion 25% 2. H+/IAA- symport (AUX1) Efflux: Membrane potential active transport PINs/ABCBs

28. PIN1 regulates auxin efflux

29. …it is localized at the basal end of the cell PIN1 is an integral membrane protein

30. PIN1 export regulator protein PIN protein is a regulator of auxin export from the cell. It is localized at the basal end of the cell Auxin can move from cell to cell

31. PIN proteins interact in networks

33. Mature tissues BR2 in maize is a AtPGP1 ortholog

34. Auxin regulates gene expression