Ethylene

1
Ethylene

• Abscission of fruits, flowers and leaves

2
The Discovery of Ethylene

• The oldest identified growth regulator
• Was used by the ancient Egyptians to cause fig
  ripening
• The Chinese burned incense in closed rooms to
  cause pear ripening
• Discovered in 1901 by Dimitry Neljubow
• In 1910 H. H. Cousins showed that plants can
  produce their own ethylene
• Discovery of Ethylene's role in abscission was in
  1917 by S Doubt
• In 1934 ethylene was shown as a natural plant
  product

3
Functions of Ethylene

• Stimulates shoot root growth differentiation
• Stimulates the release of dormancy
• May have a role in adventitious root formation
• Stimulates bromiliad flower induction
• Induction of femaleness in dioecious flowers
• Stimulates flower opening
• Stimulates flower leaf senescence
• Stimulates fruit ripening
• Stimulates leaf, fruit and flower abscission

4
Ethylene transport

• Transported as a gas
• Diffuses through the airspace
• Transported in the cytosol
• Travels from cell to cell in the symplast and
  phloem

5
Measurement of Ethylene

• Epinasty of leaves
• Flower senescence
• Root hair formation
• Leaf abscission
• Triple response
• Gas chromatography

6
Biosynthesis of Ethylene

• Ethylene is produced from L-methionine in higher
  plants
• Methionine is activated by ATP to form
  S-sdenosylmethionine
• ACC is the rate limiting step of ethylene
  production and its activity is regulated by
  factors such as wounding, drought stress,
  flooding and auxin

7
Stress induced Ethylene

• Ethylene is the stress hormone
• Wounding
• Flooding
• Drought
• Chilling
• Heating

8
Three phases of leaf abscission

• Leaf maintenance phase
• Shedding induction phase
• Shedding phase

9
Ethylenes Affects

• Cross section of a cabbage
• Stored in a room containing apples
• Ethylene produced from the apples caused
  abscission of the leaves from the stalk, even
  though the cabbage was immature

10
Ethephon

• 
  O
• 
  ll
• 
  ll
• Cl-----CH2----CH2----P----OH
  OH- ? CH2CH2 H2PO4- Cl-
• 
  l
• 
  l
• 
  O-
• 
  Ethephon
  Ethylene

• Stable at low pH, but at neutral or high pH,
  breaks down to give off ethylene
• Mixing with water is a convenient method of
  exposing plants to high doses of ethylene

11
Characterization of a non-abscission mutant in
Lupinus angustifolius. I. Genetic and Structural
aspects

• Jon Clements and Craig Atkins
• American Journal of Botany 88(1) 31-42, 2001

12
Lupinus angustifolius (Abs-)

• Spontaneous mutant (Abs-) that does not abscise
  any organ, but still maintains normal patterns of
  growth and senescence
• A recessive single gene mutation
• This mutant is specific to abscission, and may be
  caused by a lack or delay in the expression of
  hydrolytic enzymes which are specifically
  associated with abscission zone differentiation
  and separation

13
Biotechnology Relevance

• Delays in fruit ripening
• Delays in petal fading
• Delays in abscission
• Abscission limits yield and fiber quality of
  cotton