Discovery , biosynthesis , effect

1. ETHYLENE : GASEOUS
HORMONE
DONE BY:
Maha Ayman Hussien

2. Ethylene
• Ethylene is a gaseous hormone
produced by plants that aids
in the ripening and aging
process of plants. It is a
naturally occurring
hydrocarbon gas that can also
occur through combustion and
other methods

3. Ethylene Discovery
• During the nineteenth century ,
when coal gas was used for
street illumination it was
observed that the trees in the
vicinity of streetlamps defoliated
more extensively than other trees
Then they discovered that ethylene was
the
active component for coal gas

4. Properties of Ethylene
• It is the simplest alkene
• Lighter than air under
physiological conditions
• Flammable
• Can be oxidized to ethylene
oxide
• Can be completely oxidized to
CO2
• Highly active at very low
concentration

5. What Promotes Ethylene Biosynthesis ?
• Leaf abscission
• Flower senescence
• Fruit ripening
• Stress like:
Drought stress
Heat stress
Biotic stress
Wounding
Flooding

6. • Ethylene biosynthesis can be
stimulated by ACC synthetase
stabilization meaning that it is
better to increase the stability of
ACS than increasing the expression
of ACS genes
• Auxin is able to promote ethylene
synthesis by enhancing ACC
synthetase activity

7. Ethylene Diffusibility & Trapping Systems
• Ethylene is released easily from
the tissue and diffuses in the
gas phase through the intercellular
spaces and outside the tissue
• How to trap ethylene?
By potassium permanganate (KMnO4) is
an effective absorbent of ethylene
used frequently during the storage of
fruits and vegetables so it extends the
storage life of the fruit

8. Ethylene Biosynthesis
• Ethylene is derived from the amino acid
methionine, that is converted to S-adenoysl-
methionine (AdoMet) by AdoMet synthetase.
• ACC synthase (ACS) catalyzes the conversion
of AdoMet to 1-aminocyclopropane-1-carboxylic
acid (ACC), which is the first rate-limiting step
in ethylene biosynthesis.
• Then ACC oxidase catalyzes the conversion of
ACC to ethylene which is the last step

9. • The CH3-S group of
methionine is recycled via
the yang cycle
• Without this recycling the
amount of reduced sulfur
would limit methionine and
the synthesis of ethylene

10. Developmental & Physiological Effects of
Ethylene
Fruit Ripening
• Ethylene is known as aging hormone that accelerate the
ripening of some fruits
• Not all fruits responds to ethylene
climacteric fruits ripens in response to ethylene in which it
exhibits respiratory rise before the ripening phase
Non climacteric fruits don’t respond to ethylene and don’t
exhibit respiration

15. Triple Response:
• Ethylene causes ‘triple response’ of
etiolated seedling such as in pea
which consists of:
• (i) Inhibition of stem elongation,
• (ii) Stimulation of radial
swelling of stems and
• (iii) Horizontal growth of stems
with respect to gravity

16. Leaf Epinasty:
When upper side (adaxial side) of the petiole of the leaf
grows faster than the lower side (abaxial side), the leaf
curves downward. This is called as epinasty.

17.  Flowering:
• Although Ethylene is known to inhibit flowering in plants, it
induces flowering in pineapple and also mango. Ethylene is
used commercially to synchronize flowering and fruit set in
pineapple.

18.  Leaf abscission
Is the process by which plants
shed its different parts
Ethylene regulates gene
expression of cellulases and
pectinases and accelerates
abscission
Ethylene also enhances the
growth of cells in the abscission
zone generating a mechanical
force that allow shedding of
plant parts.

19.  Seed dormancy and Germination
• Ethylene breaks seed
dormancy and stimulate
seed germination
• Seeds inability to
convert ACC to ethylene
may results in reduced
seed germination

20. Formation of
Adventitious Roots and
Root Hairs:
• Ethylene induces formation
of adventitious roots in
plants from different plant
parts such as leaf, stem,
peduncle and even other
roots. In many plants
especially Arabidopsis,
ethylene treatment
promotes initiation of root
hairs

21. Ethylene Inhibitors
• 1- Aminoethoxy-vinyl-glycine (AVG)
• 2- Aminooxyacetic acid (AOA)
Blocks the conversion of AdoMet to ACC
• 3- silver ions
Potent inhibitors of ethylene action
• 4- High concentration of CO2
Inhibits the effect of ethylene such as the induction of
fruit ripening

22. Benefits of These Inhibitors
• Helps to distinguish between different hormones having
identical effects on plant.
• For example:
Ethylene mimics high concentration of auxins by inhibiting
stem growth and causing epinasty so the use of specific
inhibitors made it possible to distinguish between the action
of auxins and ethylene .
Thanks for these inhibitors that showed that ethylene is the
primary effector of epinasty and that auxin act indirectly by
causing an increase in ethylene production

23. How Ethylene is Measured?
• Gas chromatography is a very accurate and effective way in
measuring ethylene
• How it works?
Take 1ml of the sample & pass it to the column through a
carrier gas, a photoionization sensor detects ethylene
concentration

24. Ethylene Signal Transduction Pathway
Presence of Ethylene
• Ethylene binding inactivates the ethylene receptor allowing the
response to occur
1st ethylene complexes with a cupric ion
2nd ethylene binding in EIN2
3rd deactivation of CTR1
4th activation of of EIN2 that will activate the transcription
factor EIN3
5th EIN3 will travel into the nucleus and intiate the transcriptional
response of ethylene

25. Absence of Ethylene
• CTR1 will stay
activated
• No activation for
EIN2
• No signal will travel
to EIN3
• No ethylene response

27. High affinity binding of ethylene to its
receptor requires a copper cofactor
Even before the identification of ethylene receptor
scientists predicted that ethylene would bind to its receptor
via a transition metal cofactor most likely copper or zinc
This prediction was based on the high affinity of olfins for
these transition metals
Analysis of the ethylene receptor demonstrated that a
copper ion was coordinated to the protein and that this
copper was necessary for high affinity ethylene binding

28. Any substitiutions for COPPER IONS??
• Silver ion could substitute for copper to yield high affinity
binding which indicates that SILVER blocks the action of
ethylene
NOT By:
interfering with ethylene binding ,but by preventing the
changes in the protein that normally occur when ethylene
binds to the receptor.