Phototrophism

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 Wents 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 Wents Experiment
6
Phototrophism - Fritz Wents 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 -gt
• 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 1930s 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 Anns 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 --gt ripe to flower
• The juvenile stage for most conifers lasts 10 -
  20 years. Exogenous application of GA can cause
  precocious cones.

32
Cytokinins

• Discovered during the early days of tissue
  culture.
• Stewart 1930s
• carrot phloem cells coconut milk --gt
  whole plant
• Skoog 1940s
• tobacco pith cells auxin coconut medium --gt
  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 ----gt 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 cytokininauxin ratio

42
Ethylene

• A gas produced in various parts of the plant.
• (CH2CH2)
• 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 1930s.
• Promotes winter and summer dormancy.

50
Abscisic Acid

• Isolated from dormant buds in the 1930s.
• Growth inhibitor in seeds.
• ABA -----------------------gt ABA-glucoside
  cold water stress
• 
  (may wash out)

51
Abscisic Acid

• Isolated from dormant buds in the 1930s.
• 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 1600s.
• Ubiquitous in living tissue. Common biochemical
  pathway in all organisms.

55
Polyamines

• First observed as crystals in human semen by Van
  Leeuwenhooke in the 1600s.
• Ubiquitous in living tissue.
• Investigated by plant physiologists beginning in
  the 1970s. 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