Phytohormones

The growth and development of a plant are influenced by:

•Genec factors •External environmental factors •Chemical hormones inside the plant

Secondary messengers

1. Involve in the transfer informaon from sources to targets 2. Amplify the signal produced by the phytohormone

Phytohormones

Plant hormones are organic compounds that are effecve at very low concentraon

(1g 20,000 tons-1)

They interact with specific target ssues to cause physiological responses •Growth •Fruit ripening

Phytohormones

•Hormones smulate 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

Arabidopsis thaliana

Phytohormones

EARLY EXPERIMENTS ON PHOTROPISM SHOWED THAT A STIMULUS (LIGHT) RELEASED CHEMICALS THAT INFLUENCED GROWTH

Auxins

Auxin causes several responses in plants:

*

* Geotropism

* Promoon of apical dominance

* Flower formaon

* Fruit set and growth

* Formaon of advenous roots

* Differenaon of vascular ssues (de novo or repairing existent vascular ssue)

Auxins

Addion of auxins produce parthenocarpic fruit.

Stenospermocarpy Biological mechanism that produces seedlessness in some fruits (many table grapes, watermelon)

diploid + tetraploid parent = triploid vegetave parthenocarpy Plants that do not require pollinaon or other smulaon to produce parthenocarpic fruit (cucumber)

Auxins

Synthec auxins

Widely used in agriculture and horculture • prevent leaf abscission • prevent fruit drop • promote flowering and fruing • control weeds

Agent Orange - 1:1 rao 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.

Cytokinins

In 1964, zean was the first naturally occurring cytokinin isolated from corn.

Zean and zean riboside are found in coconut milk. Natural

Synthec

Cytokinins

Lateral development

Move non-polarly in •shoot iniaon Callus development xylem, phloem, and •roots <[auxin] = roots parenchyma cells. •seeds <[kinen] = buds •fruits •young leaves •chloroplast development

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

Ethylene

Most produced organic compound 107 million metric tons in 2005

Once fruit iniated red coloraon, ethylene release becomes elevated in a linear fashion (without diurnal fluctuaons).

Abscisic acid (ABA)

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 germinang

Viviparous mutants Reduced sensivity for ABA

Gibberellins

In 1930's, Ewi Kurosawa and colleagues were studying plants suffering from bakanae, or "foolish seedling" disease in rice. •Synthesized in apical porons of stems and roots

Thompson seedless grapes (Vis vinifera)

Can be readily obtained in large quanes from fermentaons of the fungus Gibberella fujikuroi •cell division and elongaon •break dormancy •speed germinaon

Gibberellins

bolng

External factors and plant growth. Tropic responses

Tropic responses Direconal movements by growth in response to a direconal smulus

Phototropism is a response to blue light Phytphormone: Auxin Second messenger: Calcium

Geotropism or Phytphormones: cytokinin and auxin

External factors and plant growth.

Thigmotropism is direconal growth response to contact with an object.

Greek thigma = touch Rapid response Diferenaon in the elongaon of the cells

tendrils External factors and plant growth. Nasc movements and heliotropism

Nasc movements are independent of the smulus' posion

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 moon of plant parts (flowers or leaves) in response to the direcon of the .

During the night, the flowers may assume a random orientaon

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 Day Night Endogenous and synchronized by the environment Biological clock

Photosynthesis Movement

External factors and plant growth. Photoperiodism

According to their photoperiods, plants can be classified into three groups: a) Short day plants. Examples: Nicoana tabacum, soybean, strawberry, and chrysanthemum. b) Long day plants. Examples: Onion, carrot and spinach. c) Day neutral plants. Examples: Tomatoes, cucumbers, sunflower, dandelions and coon.