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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
Secondary messengers 1. Involve in the transfer informa:on from sources to
targets
2. Amplify the signal produced by the phytohormone
Phytohormones
Plant hormones are organic compounds that are effec:ve at very low concentra:on (1g 20,000 tons-‐1) They interact with specific target :ssues to cause physiological responses
• Growth • Fruit ripening
Phytohormones
• Hormones s:mulate or inhibit plant growth 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
Arabidopsis thaliana
EARLY EXPERIMENTS ON PHOTROPISM SHOWED THAT A STIMULUS (LIGHT) RELEASED CHEMICALS THAT INFLUENCED GROWTH
Phytohormones
Auxin causes several responses in plants: * Phototropism * 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)
Auxins
Addi:on of auxins produce parthenocarpic fruit. 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
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 Dioxin usually contaminates 2,4,5-‐T, which is linked to miscarriages, birth defects, leukemia, and other types of cancer.
Auxins
In 1964, zea:n was the first naturally occurring cytokinin isolated from corn. Zea:n and zea:n riboside are found in coconut milk.
Natural
Synthe:c
Cytokinins
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.
Ethylene
• Is found only in the gaseous form • Induces ripening (e.g., green bananas). • Epinasty (causes leaves to droop in the fall ) • Causes abscission of fruits and flowers
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).
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
Abscisic acid (ABA)
Viviparous mutants Reduced sensi:vity for ABA
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
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)
bol6ng
Gibberellins
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 messenger: Calcium
Geotropism or gravitropism Phytphormones: cytokinin and auxin
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
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
Venus Flytrap, Dionaea muscipula. Acid growth (cells that to elongate or expand quickly at low pH) and turgor
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.
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
According to their photoperiods, plants can be classified into three groups: a) Short day plants. Examples: Nico8ana tabacum, soybean, strawberry, and
chrysanthemum. b) Long day plants. Examples: Onion, carrot and spinach. c) Day neutral plants. Examples: Tomatoes, cucumbers, sunflower, dandelions and
colon.
External factors and plant growth. Photoperiodism
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