Download Integration and Control - Academic Resources at Missouri Western

Phototrophism
• First investigated by Charles and Frances
Darwin (1881)
– canary grass Phalaris canariensis L.
– The Power of Movement in Plants (1881)
– Seedlings
• coleoptile
• plumules
Phototrophism
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.
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
Phototrophism - Fritz Went’s
Experiment
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
Phototrophism
Synthetic Auxins (precursors)
• 2, 4-D and 2,4,5-T are herbicides for broadleaved 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”
Other Normal Effects of Auxins in Plants
• 1. Phototropism
• -----• 2. Cell Elongation
– causes polysaccharide cross-bridges to break and
reform
Other Normal Effects of Auxins in Plants
• 1. Phototropism
• -----• 2. Cell Elongation
Other Normal Effects of Auxins in Plants
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1. Phototropism
-----2. Cell Elongation
3. Geotropism (Gravitropism)
4. Initiation of adventitious root growth in cuttings
5. Promotes stem elongation and inhibits root
elongation
Other Normal Effects of Auxins in Plants
– 6. Apical Dominance
Other Normal Effects of Auxins in Plants
– 6. Apical Dominance
– 7. Leaf Abscission - Abscission Layer - pectin &
–
cellulose
– ethylene ->
– pectinase &
– cellulase
Other Normal Effects of Auxins in Plants
– 7. Leaf Abscission
Other Normal Effects of Auxins in Plants
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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
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
Trypophan-dependent Biosynthesis of IAA
Gibberellins
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Isolated from a fungal disease of rice “Foolish Seedling Disease”
Gibberella fugikuroa
Isolated in the 1930’s Japan
Gibberellic Acid (GA)
Gibberellins
• Gibberellic Acid
• 125 forms of
Gibberellins
Gibberellins
• Produced mainly in apical meristems
(leaves and embryos). Are considered
terpenes (from isoprene).
Gibberellins
Gibberellins
• Produced mainly in apical meristems
(leaves and embryos).
Gibberellins
• Low concentration required for normal stem
elongation.
• Can produce parthenocarpic fruits (apples,
pears …)
Gibberellins
• Low concentration required for normal stem
elongation.
• Can produce parthenocarpic fruits (apples,
pears …)
• Important in seedling development.
– breaking dormancy
– early germination
Gibberellins
• Low concentration required for normal stem
elongation.
• Can produce parthenocarpic fruits (apples,
pears …)
• Important in seedling development.
Gibberellins
• Important in seedling development.
• Controls the mobilization of food reserves in
grasses.
Gibberellins
• Important in seedling development.
• Controls the mobilization of food reserves in
grasses.
• - cereal grains
Gibberellins
• Important in seedling development.
• Controls the mobilization of food reserves in
grasses.
Gibberellins
• Controls bolting in rosette-type plants.
– Lettuce, cabbage
(photoperiod)
– Queen Ann’s lace,
Mullein
(cold treatment)
– premature bolting
Gibberellins
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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.
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 10 - 20
years. Exogenous application of GA can cause
precocious cones.
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
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“CYTOKININ”
Cytokinins
• ZEATIN - most abundant cytokinin in plants.
– Adenine is the basic building block.
Terpene Biosynthesis - cytokinin
(Can be made from isoprene via the melvonic acid pathway.)
• Produced mainly in apical root meristems.
Cytokinins
• Transported “up” the plant in the xylem
tissue.
• Mainly affects cell division.
– “Witches’ Broom”
• mistletoe; bacterial, viral or fungal infection
Cytokinins
– “Witches’ Broom”
• mistletoe; bacterial, viral or fungal infection
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.
Cytokinins
– Play an antagonistic role with auxins in apical
dominance.
Cytokinins
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Promotes leaf expansion.
Prevents senescence.
Promotes seed germination in some plants.
Both cytokinins and auxins are needed for
plant tissue cultures.
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
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
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)
Ethylene
• Can be made from the amino acid
methionine (S)
• Promotes leaf curling (epinasty).
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.
Ethylene
– Causes hypocotyl hook & plumular arch.
Ethylene Signal Transduction Pathway
• Arabidopsis mutants
• Silver Thiosulfate
Abscisic Acid
• Produced mainly in leaves (chloroplasts)
and transported through the phloem.
Terpene Biosynthesis - Abscisic Acid
(Can be made from isoprene via the melvonic acid pathway.)
•
Abscisic Acid
• Isolated from dormant buds in the 1930’s.
– Promotes “winter’ and “summer dormancy”.
Abscisic Acid
• Isolated from dormant buds in the 1930’s.
• Growth inhibitor in seeds.
– ABA -----------------------> ABA-glucoside
cold
water stress
–
(may wash out)
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.)
Brassinosteroids
• Found in Brassica rapus.
• Isolated from most tissues.
• Polyhydrated Sterol
Brassinosteroids
• Found in Brassica napus.
• Isolated from most tissues.
• Stimulates shoot elongation, ethylene
production; inhibits root growth and
development.
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.
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.
Phytohormones, Senescence and
Fall Color Change in
Deciduous Trees