1. Phototrophism First investigated by Charles and Frances Darwin (1881)
canary grass Phalaris canariensis L.
The Power of Movement in Plants (1881)
Seedlings
coleoptile
plumules

2. Phototrophism

3. Phototrophism - Darwins’ Experiment
Conclusion:
Some chemical is produced in the tip and transmitted down the stem to somehow produce bending.
There is a growth-promoting messenger.

4. Phototrophism - Fritz Went’s Experiment
Dutch Plant Physiologist 1929
Oat seedlings
Diffusion of phytohormone from growing tip in agar blocks
Agar blocks placed on oat seedlings

5. Phototrophism - Fritz Went’s Experiment

6. Phototrophism - Fritz Went’s Experiment
Conclusion:
A growth substance (phytohormone) must be (1) produced in the tip; (2) transmitted down the stem; and somehow (3) accumulate on the side away from the light.
“Auxin” (to increase, by Went)
Either
H.1: is destroyed on the lighted side or
H.2: migrates to the dark side

7. Phototrophism

8. Synthetic Auxins (precursors)
2, 4-D and 2,4,5-T are herbicides for broad-leaved plants at very low concentrations.
Widely used commercially for 30 years - defoliant in Viet Nam.
Contaminant of 2,4,5-T
tetrachlorobenzo-para-dioxin “dioxin”

9. Other Normal Effects of Auxins in Plants
1. Phototropism
------
2. Cell Elongation
causes polysaccharide cross-bridges to break and reform

10. Other Normal Effects of Auxins in Plants
1. Phototropism
------
2. Cell Elongation

11. Other Normal Effects of Auxins in Plants
1. Phototropism
------
2. Cell Elongation
3. Geotropism (Gravitropism)
4. Initiation of adventitious root growth in cuttings
5. Promotes stem elongation and inhibits root elongation

12. Other Normal Effects of Auxins in Plants
6. Apical Dominance

13. Other Normal Effects of Auxins in Plants
6. Apical Dominance
7. Leaf Abscission - Abscission Layer - pectin &
cellulose
ethylene ->
pectinase &
cellulase

14. Other Normal Effects of Auxins in Plants
7. Leaf Abscission

15. Other Normal Effects of Auxins in Plants
1. Phototropism
2. Cell Elongation
3. Geotropism (Gravitropism)
4. Initiation of adventitious root growth in cuttings
5. Promotes stem elongation and inhibits root elongation
6. Apical Dominance
7. Leaf Abscission
8. Maintains chlorophyll in the leaf
9. Seedling Growth
10. Fruit Growth (after fertilization)
11. Parthenocarpic development

16. Auxins Work at very small concentrations (500 ppm)
Action Spectrum: primarily blue
Tryptophan is the primary precursor
Auxins must be inactivated at some point by forming conjugates or by enzymatic break down by enzymes such as IAA oxidase

17. Trypophan-dependent Biosynthesis of IAA

18. Gibberellins Isolated from a fungal disease of rice -
“Foolish Seedling Disease”
Gibberella fugikuroa
Isolated in the 1930’s Japan
Gibberellic Acid (GA)

19. Gibberellins
Gibberellic Acid
125 forms of Gibberellins

20. Gibberellins
Produced mainly in apical meristems (leaves and embryos). Are considered terpenes (from isoprene).

21. Gibberellins

22. Gibberellins
Produced mainly in apical meristems (leaves and embryos).

23. Gibberellins Low concentration required for normal stem elongation.
Can produce parthenocarpic fruits (apples, pears …)

24. Gibberellins Low concentration required for normal stem elongation.
Can produce parthenocarpic fruits (apples, pears …)
Important in seedling development.
breaking dormancy
early germination

25. Gibberellins Low concentration required for normal stem elongation.
Can produce parthenocarpic fruits (apples, pears …)
Important in seedling development.

26. Gibberellins Important in seedling development.
Controls the mobilization of food reserves in grasses.

27. Gibberellins Important in seedling development.
Controls the mobilization of food reserves in grasses.
- cereal grains

28. Gibberellins Important in seedling development.
Controls the mobilization of food reserves in grasses.

29. Gibberellins Controls bolting in rosette-type plants.
Lettuce, cabbage (photoperiod)
Queen Ann’s lace, Mullein (cold treatment)
premature bolting

30. Gibberellins Controls bolting in rosette-type plants.
Important factor in bud break.
Promotes cell elongation and cell division.
Antisenescent.
Transported in both the phloem and xylem.
Application of GA to imperfect flowers causes male flower production. (monoecious, dioecious)
Probably function by gene regulation and gene expression.

31. Gibberellins
Application of GA to imperfect flowers causes male flower production. (monoecious, dioecious)
Probably function by gene regulation and gene expression.
Promotes flower and fruit development.
“juvenile stage” --> “ripe to flower”
The juvenile stage for most conifers lasts years. Exogenous application of GA can cause precocious cones.

32. Cytokinins Discovered during the early days of tissue culture.
Stewart 1930’s
carrot phloem cells + coconut milk --> whole plant
Skoog 1940’s
tobacco pith cells + auxin & coconut medium --> whole plant
“CYTOKININ”

33. Cytokinins ZEATIN - most abundant cytokinin in plants.
Adenine is the basic building block.

34. Terpene Biosynthesis - cytokinin (Can be made from isoprene via the melvonic acid pathway.)
Produced mainly in apical root meristems.

35. Cytokinins Transported “up” the plant in the xylem tissue.
Mainly affects cell division.
“Witches’ Broom”
mistletoe; bacterial, viral or fungal infection

36. Cytokinins “Witches’ Broom”
mistletoe; bacterial, viral or fungal infection

37. Cytokinins “Crown Gall”
a neoplasic growth due to infection by Agrobacterium tumifaciens.
A. tumifaciens carries the genes for production of cytokinin and auxins on a plasmid. Plasmid genes become a part of host cell genome.

38. Cytokinins
Play an antagonistic role with auxins in apical dominance.

39. Cytokinins Promotes leaf expansion. Prevents senescence.
Promotes seed germination in some plants.
Both cytokinins and auxins are needed for plant tissue cultures.

40. Cytokinins
Both cytokinins and auxins are needed for plant tissue cultures. (Skoog and others…)
Cell Initiation Medium (CIM)
Approximately equal amounts of cytokinin and auxins will proliferate the production of undifferentiated callus.
EXPLANT ----> CIM

41. Cytokinins
Both cytokinins and auxins are needed for plant tissue cultures. (Skoog and others…)
Cell Initiation Medium (CIM)
Root Growth Medium (RIM)
Shoot Growth medium (SIM)
High cytokinin:auxin ratio

42. Ethylene A gas produced in various parts of the plant. (CH2=CH2)
Production promoted by various types of stress - water stress, temperature, wounding & auxins.
Can be made from the amino acid methionine (S)

43. Ethylene Can be made from the amino acid methionine (S)
Promotes leaf curling (epinasty).

44. Ethylene Can be made from the amino acid methionine (S)
Promotes leaf curling (epinasty).
Promotes senescence.
Promotes fruit ripening.
Promotes etioloation & hypocotyl hook.
Is autocatalitic.
Promotes bud dormancy.
Inhibits cell elongation.

45. Ethylene
Causes hypocotyl hook & plumular arch.

46. Ethylene Signal Transduction Pathway
Arabidopsis mutants
Silver Thiosulfate

47. Abscisic Acid
Produced mainly in leaves (chloroplasts) and transported through the phloem.

48. Terpene Biosynthesis - Abscisic Acid (Can be made from isoprene via the melvonic acid pathway.)

49. Abscisic Acid Isolated from dormant buds in the 1930’s.
Promotes “winter’ and “summer dormancy”.

50. Abscisic Acid Isolated from dormant buds in the 1930’s.
Growth inhibitor in seeds.
ABA > ABA-glucoside cold water stress
(may wash out)

51. Abscisic Acid Isolated from dormant buds in the 1930’s.
Growth inhibitor in seeds.
Causes stomatal closure.
(Response to chloroplast membrane changes during water stress.)

52. Brassinosteroids Found in Brassica rapus. Isolated from most tissues.
Polyhydrated Sterol

53. Brassinosteroids Found in Brassica napus. Isolated from most tissues.
Stimulates shoot elongation, ethylene production; inhibits root growth and development.

54. Polyamines
First observed as crystals in human semen by Van Leeuwenhooke in the 1600’s.
Ubiquitous in living tissue. Common biochemical pathway in all organisms.

55. Polyamines
First observed as crystals in human semen by Van Leeuwenhooke in the 1600’s.
Ubiquitous in living tissue.
Investigated by plant physiologists beginning in the 1970’s. Effect on macromolecules and membranes discovered.
Role in normal cell functioning in both prokaryotic and eukaryotic cells.
Growth factor.

56. Phytohormones, Senescence and Fall Color Change in Deciduous Trees