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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 :

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Phototrophism

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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 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”


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

  • 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

  • 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

  • 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

  • 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

    • “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


“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


Cytokinins

  • Play an antagonistic role with auxins in apicaldominance.


Cytokinins

  • 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


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