1. Plant Hormones 101
MUPGRET Workshop

2. What are hormones?
“a group of naturally occurring organic compounds that influence physiological processes at low concentrations.”
“a substance that is transferred from one part of an organism to another.”
From: Plant Hormones: Biosynthesis, Signal Transduction, Action! Peter Davies, ed.
From: Went and Thimann Phytohormones.

3. Hormones
Can be synthesized locally or transported to their site of action.
They differ from mammalian hormones in this respect.

4. The first hormone Auxin Fits the original definition of a hormone.
Transported from site of synthesis to site of action.

5. Sachs
Hypothesized root forming and flowering forming compounds move through the plants and cause morphological changes in 1880.

6. Darwin First to observe phototropism, the bending of a plant to light.
Also in 1880.
Hypothesized that redistribution of a chemical within the young seedling caused it to bend toward the light.

7. Auxin Darwin’s compound that caused phototrophism.
Isolated several years later by extracting the chemicals that diffused from cut coleoptiles into blocks of agar.
More about this compound tomorrow when Dr. Hagen talks.

8. Classical Plant Hormones
Auxin
Gibberellins
Cytokinins
Abscisic Acid
Ethylene

9. New generation plant hormones
Brassinosteriods
Salicylic acid
Peptides
Polyamines

11. Auxin Indole-3-acetic acid (IAA) and its conjugates.
Synthesized from tryptophan or indole in leaf primodia, young leaves and developing seed.
IAA Structure

12. Auxin Transport In vascular cambium and procambial strands.
Possibly between epidermal cells.
Transport to root may occur through phloem.

13. Auxin Stimulates Cell enlargement Stem growth Cell division in cambium
Phloem and xylem differentiation
Root initiation
Root branching
Phototropism
Floral organ growth

14. Auxin functions to Delay leaf senescence Promote apical dominance
Delay fruit ripening

15. Auxin mutant
Brachytic 2 (br2) mutant in maize.

16. Gibberellin Family of 125 compounds.
Gibberellin acid (GA3)is the most common.
Synthesized in young shoots and developing seed.

17. Gibberellins Chloroplast is the initial site of synthesis.
Transported in phloem and xylem.

18. Gibberellin promotes Stem elongation
Cell division and elongation in stems
Germination if cold or light treatment is required.
Enzyme production, eg. α-amylase.
Fruit set

19. Gibberellin mutant Dwarf 8 (D8) mutant in maize.
The same gene in wheat is responsible for the Green Revolution.
Introduction of this gene into cultivated wheat earned Norman Borlaug the Nobel Prize.

20. Cytokinins Adenine derivatives. Zeatin is the most common.
Synthesized in root tips and developing seed.
Transported in xylem.

21. Cytokinin promotes Cell division if auxin is present.
Photomorphogenesis, eg. Crown gall formation
Lateral bud growth
Leaf expansion by cell enlargement
Stomatal opening
Chloroplast development

22. Cytokinin delays
Leaf senescence

23. Ethylene H2C=CH2 Gas Synthesized from methionine
Most tissues can synthesize ethylene in response to stress.
Chemical Structure

24. Ethylene Transport occurs by diffusion.
Not absolutely required for growth.
Mutants with non-functional ethylene gene develop normally.

25. Ethylene causes The triple response in dark Reduced stem elongation
Stem thickening
Lateral growth

26. Ethylene stimulates Defense response to wounding or disease
Release from dormancy
Shoot growth and differentiation
Root growth and differentiation
Adventitious root formation
Leaf and fruit abscission

27. Ethylene stimulates
Flower opening
Fruit ripening

28. Abscisic Acid
Synthesized from glyceraldehyde-3-phosphate through carotenoid pathway.
Synthesized in roots, mature leaves, and seeds.

29. Abscisic Acid Synthesis increases in response to drought.
Transported from roots in xylem.
Transported from shoots in phloem.

30. ABA stimulates Stomatal closure Root growth under water stress.
Storage protein synthesis in seeds.
Breaking dormancy
Defense response

31. ABA inhibits
Shoot growth under water stress.

32. Abscisic Acid Mutant
viviparous 5 (vp5) mutant in maize.

33. Polyamines Aliphatic amines.
Putrescine, spermidine and spermine are most common.
Effective at low concentrations.
Mutants have abberant development.
NH2
H2N
Spermidine structure

34. Brassinosteroids Sixty steroidal compounds.
Effective at low concentrations.
Brassinolide structure

35. Brassinosteriods stimulate
Cell division
Cell wall loosening
Vascular differentiation
Ethylene biosynthesis

36. Brassinosteroids Required for fertility
Inhibit root development and growth

37. Jasmonates Jasmonic acid is most common Methyl esters Scented
Methyl jasmonate

38. Jasmonate function Induce tuberization Important in plant defense
Inhibit growth
Inhibit germination
Promote senescence
Promote pigmentation

39. Salicylic Acid Synthesized from phenylalanine.
Promotes production of pathogenesis related proteins.
Can reverse effects of ABA in some cases.

40. Signal Peptides
Small molecules that can be transported throughout the plant and effect development.
Involved in defense response
Help determine cell fate
Involved in self-incompatibility
Involved in nodule formation in legumes