1. Growth regulators 1.Auxins 2.Cytokinins 3.Gibberellins 4.Abscisic acid 5.Ethylene 6.Brassinosteroids All are small organics: made in one part, affect another part

2. Growth regulators All are small organics: made in one part, affect another part Treating a plant tissue with a hormone is like putting a dime in a vending machine. It depends on the machine, not the dime!

3. Auxin 1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark Uneven amounts of "transmissible influence" makes bend 1926: Went showed that a chemical that diffused from tips into blocks caused growth If placed asymmetrically get bending due to asymmetrical growth Amount of bending depends on [auxin] = assay 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending

4. Auxin 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending IAA is the main auxin in vivo. Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA)IBA PA 4-CI-IAA IAA

5. Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identifiedIAA

6. Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work!IAA

7. Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agricultureIAA

8. Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agriculture to promote growth (flowering, cuttings)IAA

9. Auxin IAA is the main auxin in vivo. Many synthetic auxins have been identified No obvious structural similarity, yet all work! Widely used in agriculture to promote growth (flowering, cuttings) as weed killers! Agent orange was 1:1 2,4-D and 2,4,5-TIAA

10. Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T 2,4,5-T was contaminated with dioxin, a carcinogenIAA

11. Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T 2,4,5-T was contaminated with dioxin, a carcinogen 2,4-D is still widely used: selectively kills dicotsIAA

12. Auxin weed killers! 2,4-D is still widely used: selectively kills dicots Controls weeds in monocot crops (corn, rice, wheat) Mech unclear: may cause excess ethylene or ABA production.IAA

13. Auxin weed killers! 2,4-D is still widely used: selectively kills dicots Controls weeds in monocot crops (corn, rice, wheat) Mech unclear: may cause excess ethylene or ABA production.IAA

14. Auxin >90%of IAA is conjugated to sugars in vivo!

15. Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated!

16. Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay!

17. Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay! Critical concentration varies between tissues

18. Auxin >90%of IAA is conjugated to sugars in vivo! Inactive, but readily activated! Best way to measure [auxin] is bioassay! Critical concentration varies between tissues Roots are much more sensitive than leaves!

19. Auxin Critical concentration varies between tissues Roots are much more sensitive than leaves! Made in leaves & transported to roots so [IAA] decreases going down the plant Most cells are IAA sinks!

20. Auxin Synthesis Made in leaves & transported to roots so [IAA] decreases going down the plant Most is made from trp

21. Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp

22. Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp Path used varies between tissues

23. Auxin Synthesis Most is made from trp Also made by trp-independent pathway: exits before trp Path used varies between tissues No way to run out of IAA

24. Auxin Levels No way to run out of IAA! [IAA] depends on metabolism

25. Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks!

26. Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal

27. Auxin Levels No way to run out of IAA! [IAA] depends on metabolism Most cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal IAA transport therefore affects growth & development

28. Auxin Transport IAA transport therefore affects growth & development is polar and basipetal: New roots form at base of stem even if stored upside-down

29. Auxin Transport IAA transport therefore affects development: is polar and basipetal. New roots form at base of stem even if stored upside-down. Stem sections only move IAA basipetally