Phytohormones - Napa Valley College · Phytohormones$ Results on growth of coleoptiles of canary...
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Transcript of Phytohormones - Napa Valley College · Phytohormones$ Results on growth of coleoptiles of canary...
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The growth and development of a plant are influenced by:
• Gene:c factors • External environmental factors • Chemical hormones inside the plant
Receptor Ac:va:on or repression of sets of genes in the nucleus
Secondary messengers mediate the phytohormone responses
1. Involve in the transfer informa:on from sources to targets
2. Amplify the signal produced by the phytohormone
Hormone, from the Greek word horman, meaning "to s:mulate”.
Hormones control • Growth • Development • Movement.
Phytohormones
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Plant hormones are chemical messengers
Hormones are organic compounds that are effec:ve at very low concentra:on (1g 20,000 tons-‐1)
Usually synthesized in one part of the plant and are transported to another loca:on.
They interact with specific target :ssues to cause physiological responses • Growth • Fruit ripening
Each response is oWen the result of two or more hormones ac:ng together.
Phytohormones
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• Hormones s:mulate or inhibit plant growth
• Growth regulators rather than s:mulators.
Major groups of hormones: 1. Auxins 2. Gibberellins 3. Ethylene 4. Cytokinins 5. Abscisic acid 6. Brassinostereoids 7. Salicylic acid 8. Polyaminas 9. Jasmonates 10. Systemin 11. Nitric oxide
Phytohormones
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Results on growth of coleoptiles of canary grass and oats suggested that the reception of light in the tip of the shoot stimulated a bending toward light source.
EARLY EXPERIMENTS ON PHOTROPISM SHOWED THAT A STIMULUS (LIGHT) RELEASED CHEMICALS THAT INFLUENCED GROWTH
Phytohormones
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Auxin causes several responses in plants:
* Bending toward a light source (phototropism)
* Downward root growth in response to gravity (geotropism)
* Promo:on of apical dominance
* Flower forma:on
* Fruit set and growth
* Forma:on of adven::ous roots
* Differen:a:on of vascular :ssues (de novo or repairing existent vascular :ssue)
Precursors of hydathodes produced auxins
Auxins
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Addi:on of auxins produce parthenocarpic fruit.
Natural or ar:ficially induced produc:on of fruit without fer:liza:on of ovules.
Stenospermocarpy Biological mechanism that produces seedlessness in some fruits (many table grapes, watermelon)
diploid + tetraploid parent = triploid seeds
vegeta6ve parthenocarpy Plants that do not require pollina:on or other s:mula:on to produce parthenocarpic fruit (cucumber)
Auxins
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polar auxin (IAA) transport
Acropetal transport
Basipetal transport
• Passive diffusion • Ac:ve transport
Auxins
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Synthe:c auxins
Widely used in agriculture and hor:culture • prevent leaf abscission • prevent fruit drop • promote flowering and frui:ng • control weeds
Agent Orange -‐ 1:1 ra:o of 2,4-‐D and 2,4,5-‐T used to defoliate trees in Vietnam War.
Dioxin usually contaminates 2,4,5-‐T, which is linked to miscarriages, birth defects,leukemia, and other types of cancer.
Auxins
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In 1964, zea:n was the first naturally occurring cytokinin isolated from corn.
Zea:n and zea:n riboside are found in coconut milk.
All cytokinins (ar:ficial or natural) are chemically similar to adenine.
Cytokinin from Cytokinesis
Natural
Synthe:c
Cytokinins
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Cytokinins
Callus development <[auxin] = roots <[kine6n] = buds
• shoot ini6a6on • roots • seeds • fruits • young leaves • chloroplast development
Lateral bud development
Move non polarly in xylem, phloem, and parenchyma cells.
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Ethylene • Is found only in the gaseous form • Induces ripening (e.g., green bananas). • Epinasty (causes leaves to droop in the fall ) • Non polarly in xylem, phloem, and parenchyma cells. • Causes abscission of fruits and flowers
Ethylene was first detected as flower buds opened and exhibited diurnal oscilla:ons with peak produc:on prior to petal abscission
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Plants oWen increase ethylene produc:on in response to stress
Is found in high concentra:ons within cells at the end of a plant's life.
Methionine is the precursor of ethylene
Most produced organic compound 107 million metric tons in 2005
Ethylene
Once fruit ini:ated red colora:on, ethylene release becomes elevated in a linear fashion (without diurnal fluctua:ons).
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Abscisin is made from carotenoids and moves non-‐polarly through plant :ssue.
Abscisic acid (ABA) is a general plant-‐growth inhibitor.
Induces dormancy Prevents seeds from germina:ng
High concentra:ons of ABA in guard cells during periods of drought stress play a role in stomatal closure
Abscisic acid (ABA)
Viviparous mutants Reduced sensi:vity for ABA
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In 1930's, Ewi: Kurosawa and colleagues were studying plants suffering from bakanae, or "foolish seedling" disease in rice.
• Synthesized in apical por:ons of stems and roots • Transport is non-‐polar
Can be readily obtained in large quan::es from fermenta:ons of the fungus Gibberella fujikuroi
• cell division and elonga:on • break seed dormancy • speed germina:on
Gibberellins
Thompson seedless grapes (Vi/s vinifera)
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bol6ng
Gibberellins
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External factors and plant growth. Tropic responses
Tropic responses Direc:onal movements by growth in response to a direc:onal s:mulus
Phototropism is a response to blue light Phytphormone: Auxin Second mesenger: Calcium
Geotropism or gravitropism Phytphormones: cytokinin and auxin
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Starch -‐ statolith hypothesis: Gravity has caused amyloplast to fall inside this statocyte, lodging them against other cell components. Protoplast pressure hypothesis:
The weight of the en:re mass of the protoplast is involved in the percep:on.
Tesengrity model
Tension between structural components
External factors and plant growth. Geotropism
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Thigmotropism is direc:onal growth response to contact with an object.
tendrils
Greek thigma = touch Rapid response Diferen:a:on in the elonga:on of the cells
External factors and plant growth. Thigmotropism
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External factors and plant growth. Nas6c movements and heliotropism
Nas:c movements are independent of the s:mulus' posi:on
Touch, mechanical, electrical, thermal or chemical
In Mimosa pudica. change in the osmo:c poten:al (turgor) of cells of the pulvinus due to the movement of K+ ions and contrac:on of the cytoskeleton 1cm/sec.
Venus Flytrap, Dionaea muscipula. Acid growth (cells that to elongate or expand quickly at low pH) and turgor (> 1 second)
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External factors and plant growth. Heliotropism
Heliotropism is the diurnal mo:on of plant parts (flowers or leaves) in response to the direc:on of the sun.
During the night, the flowers may assume a random orienta:on
Heliotropism is a response to blue light.
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External factors and plant growth. Circadian rhythms
Roughly 24-‐hour cycle in the biochemical, physiological, or behavioral organisms’ processes
Hours of light
Endogenous and synchronized by the environment Biological clock
Photosynthesis Movement
Night Day
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According to their photoperiods, plants can be classified into three groups:
a) Short day plants. Examples: Nico7ana tabacum, soybean, strawberry, and chrysanthemum.
b) Long day plants. Examples: Onion, carrot and spinach. c) Day neutral plants. Examples: Tomatoes, cucumbers, sunflower, dandelions and
coqon.
Phytocromes are the photoreceptors for photoperiodism
External factors and plant growth. Photoperiodism