Ethylene

Discovery

1901 Neljubow in St. Petersburg Russia:

Coal gas = illuminating gas in cities (gas lights)
Causes triple response: dwarf stem, fat stem, agravitropism in stem in peas also leaf abscission in nearby trees
Identified ethylene from the gas as the causative agent.
(OLDEST IDENTIFIED GROWTH REGULATOR)

1910 Oranges cause bananas to ripen prematurely (natural ethylene?)

1934 Ethylene is a natural product (plant hormone?)

Forgotten for many years as possible hormone....

1959 Burg & Thimann rediscover old research and begin studies showing ethylene as possible hormone

What is ethylene?

Simplest olefin hydrocarbon: C₂H₄
Gas at room temperature
Flammable
Oxidizes to ethylene oxide C₂H₄O and ultimately ethylene glycol OH-C₂H₄-OH

Controlling the Pool Size

Synthesis:

Methionine->S-adenosylmethionine->aminocyclopropanecarboxylic acid->ethylene

Pathway elucidated completely in 1979 (Adams & S. F. Yang)
ACC synthase (usually limiting enzyme in path)
Ethylene Forming Enzyme (sometimes limiting, esp fruit senescence)

Degradation:

Ethylene -> Ethylene oxide C₂H₄O -> oxalic acid HOOC-COOH -> 2 CO₂

Transport:

Gas generally diffuses rapidly but not under waterlogging immersion.
ACC is transported in nonpolar way

Adsorption on charcoal and KMnO₄ (potassium permanganate)

Ventilation important!

Conjugation:

ACC ---> Malonyl ACC--NOT STORAGE...irreversible

Pool Size:

1 uL/L (= 1 ppm) is active in most responses

Stress and IAA stimulate ethylene biosynthesis at ACC synthase

Receptors: Bind Ag+ ions and CO₂ as well as C₂H₄ and contains Cu cofactor

EFFECTS

Fruit Ripening

Abscission; leaf flower fruits (thinning, harvesting)

Epinasty

Triple Resonses

Hook Closure Maintenance

Initiates Germination in Grains

Activates dormant buds (potatoes in storage)

Stem elongation in deep-water rice

Induces Flowering in Pineapple

Promotes Female Expression in Flowers

Flower and Leaf Senescence: Ag preventative (vase life)

Go back to the Course Schedule