Integration and Control • Animals?

• Plants?

Integration and Control • Animals?

–nervous impulses & hormones • Plants?

–phytohormones

Important Plant Functions • Growth -

– increase in size • increase organs - roots, stems, leaves – orient favorably in the environment • seedling growth • growth of adult organs (?)

Phototropism

• First investigated by Charles and Frances Darwin (1881) – canary grass

Phalaris canariensis

L

.

– The Power of Movement in Plants (1881) – Seedlings • coleoptile • plumules

Phototropism

Phototropism - 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.

Phototropism - 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

Phototropism - Fritz Went’s Experiment

Phototropism - 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

Phototropism

Distribution of Auxin in an Oat Seedling (

Avena savita

) • Auxins are produced in growing tips (meristems); transmitted in the phloem. Basipetal, Acropetal

Distribution of Auxin in an Oat Seedling (

Avena savita

) • Polar Transport * Auxins are produced in growing tips (meristems); transmitted in the phloem. Basipetal, Acropetal Influx carriers basal efflux carriers Becomes protonate in CW space

Distribution of Auxin in an Oat Seedling (

Avena savita

) • Polar Transport * Auxins are produced in growing tips (meristems); transmitted in the phloem. Basipetal, Acropetal Influx carriers protonate IAA basal efflux carriers nonprotonate IAA Becomes protonate in CW space

Naturally Occurring Auxins

have been chemically isolated and analyzed (acid side chain on a aromatic ring) • Fig15-2a

Synthetic Auxins (precursors)

• Fig15-2b

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 extensins

Other Normal Effects of Auxins in Plants 2. Cell Elongation extensins Phytohormones serve as signals - signal receptionion transduction response

Other Normal Effects of Auxins in Plants • 1. Phototropism • ----- • 2. Cell Elongation • 3. Geotropism

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

Other Normal Effects of Auxins in Plants • • 11. Parthenocarpic development (Pollination -> fertilization -> ovary development) – Massart 1902 • dead pollen grains -> fruit development in orchids – Fitting 1910 • pollen extract -> fruit development in orchids – Yasuda 1934 • pollen extract -> fruit development in cucumbers • pollen extract -> auxins (IAA) – Gustafson 1936 • IAA paste -> fruit development in several plants

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

Bound Auxins (To inactivate - IAA-conjugates)

Bound Auxins (To inactivate - IAA-conjugates)

Bound Auxins (To inactivate - Decarboxylation)

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 • At least 125 different forms.

• Produced mainly in apical meristems.

• Low concentration required for normal stem elongation.

Gibberellins • Low concentration required for normal stem elongation.

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

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 • 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.

Gibberellins • Controls bolting in rosette-type plants.

• Important factor in bud break.

• Promotes cell elongation and cell division.

Gibberellins • Controls bolting in rosette-type plants.

• Important factor in bud break.

• Promotes cell elongation and cell division.

• Antisenescent.

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.

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)

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.

Gibberellins • Promotes flower and fruit development.

– “juvenile stage” --> “ripe to flower”

Antigibberellins - Growth Retardants • Block steps in Gibberellin biosynthesis. Prevents “lodging”.

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.

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 • Promotes

leaf expansion

.

• Prevents

senescence

.

• Promotes

seed germination

in some plants.

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

) • High auxin:cytokinin ratio

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

.

– declining metabolic rates – decrease in protein synthesis – (Daylight and temperature affects production.)

Ethylene • Can be made from the amino acid

methionine

(S) • Promotes

leaf curling

(epinasty).

• Promotes

senescence

.

• Promotes

fruit ripening

.

Ethylene • Can be made from the amino acid

methionine

(S) • Promotes

leaf curling

(epinasty).

• Promotes

senescence

.

• Promotes

fruit ripening

.

• Promotes

etioloation

and the maintenance of the

hypocotyl hook

and

plumular arch

.

• Is

autocatalitic

.

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