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Ethylene
Abscission of fruits,
flowers and
leaves
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
Functions of Ethylene
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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
Ethylene transport
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Transported as a gas
Diffuses through the airspace
Transported in the cytosol
Travels from cell to cell in the symplast and
phloem
Measurement of Ethylene
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Epinasty of leaves
Flower senescence
Root hair formation
Leaf abscission
Triple response
Gas chromatography
Biosynthesis of Ethylene
• Ethylene is produced from
L-methionine in higher
plants
• Methionine is activated by
ATP to form Ssdenosylmethionine
• ACC is the rate limiting
step of ethylene
production and its activity
is regulated by factors
such as wounding,
drought stress, flooding
and auxin
Stress induced Ethylene
• Ethylene is the stress
hormone
• Wounding
• Flooding
• Drought
• Chilling
• Heating
Three phases of leaf abscission
• Leaf maintenance phase
• Shedding induction
phase
• Shedding phase
Ethylene’s 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
Ethephon
O
ll
ll
Cl-----CH2----CH2----P----OH + OH-  CH2===CH2 + H2PO4- + Cll
l
OEthephon
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
Characterization of a nonabscission mutant in Lupinus
angustifolius. I. Genetic and
Structural aspects
Jon Clements and Craig Atkins
American Journal of Botany 88(1):
31-42, 2001
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
Biotechnology Relevance
• Delays in fruit
ripening
• Delays in petal fading
• Delays in abscission
• Abscission limits yield
and fiber quality of
cotton