Molecular And Biochemical Steps In Biosynthesis Of Ethylene In Plant

1. MOLECULAR AND BIOCHEMICAL STEPS IN
BIOSYNTHESIS OF ETHYLENE IN PLANT
Course No. PP - 504
Course Title - Hormonal regulation of plant growth and development
Submitted to,
Dr. M.M.Burondkar
Prepared by,
Name- CHAVAN MAHADEO RAJARAM
Reg. No.- ADPM/15/2419
Class- Jr. M. Sc. Agriculture
Genetics and Plant Breeding

2. Ethylene
Ethylene is a gaseous plant hormone that affects
developmental processes and fitness responses, including
germination, flower and leaf senescence, fruit ripening, leaf
abscission, root nodulation and responsiveness to stress and
pathogen attack.
 Ethylene is the plant hormone mainly responsible for
ripening of fruits.
 It is gas, CH2=CH2or C2H4 at room temperature and is
produced in minute quantities by plant tissues & active at
low concentrations(well below 1 part in 10 million of air).

3. H H
/
C = C
/
H H
 Ethylene is not easily soluble in aqueous medium and
volatilizes into the intercellular space from where it is released in
the outer atmosphere.
 The meristems and the nodes are the chief sites for the
production of ethylene.
Chemical Formula of ethylene -

4. In 1901, Dimitry Neljubow demonstrated that the gas
ethylene was the active factor which caused leaves to
drop from trees that were near leaking gas mains.
 Plants produce ethylene in response to stresses
such as drought, flooding, mechanical pressure,
injury, and infection.
 Ethylene production also occurs during fruit
ripening and during programmed cell death.
 Ethylene is also produced in response to high
concentrations of externally applied auxins.

5. • Ethylene instigates a seedling to perform a
growth maneuver called the triple response that
enables a seedling to circumvent an obstacle.
• Ethylene production is
induced by mechanical
stress on the stem tip.
• In the triple response, stem
elongation slows, the stem
thickens, and curvature
causes the stem to start
growing horizontally.

6. • As the stem continues to grow horizontally, its tip
touches upward intermittently.
– If the probes continue to detect a solid object above,
then another pulse of ethylene is generated and the stem
continues its horizontal progress.
– If upward probes detect no solid object, then ethylene
production decreases, and the stem resumes its normal
upward growth.
• It is ethylene, not the physical obstruction per se,
that induces the stem to grow horizontally.
– Normal seedlings growing free of all physical
impediments will undergo the triple response if ethylene
is applied.

7. • Arabidopsis mutants with abnormal triple
responses have been used to investigate
the signal transduction pathways leading
to this response.
–Ethylene-insensitive (ein) mutants fail to
undergo the triple response after exposure to
ethylene.

8. Site of synthesis:-
• It is naturally produced in plants & synthesized
from any part of the plant.
• The production of ethylene in accelerated at the
time of ripening of fruits, leaf fall, senescing
flowers, injuries, drought stress etc.
• Maturing fruits, meristematic region, nodal region
are the sites of actively synthesis .
Synthesis :-
• Ethylene get synthesised naturally in mature
fruits, aging leaves etc.
• Physiological stress like - wounding, bruising,
flooding, chilling, temperature, cutting etc.

9. Biosynthesis Pathway of Ethylene
Methionine
ATP Ado Met Synthatase
ADP+Pi
S-Adenosyl Methionine(AdoMet)
ACC Synthase
1-Amino cyclopropane-1 –Carboxylic acid(ACC)
½ O2 ACC Oxidase
HCN+O2
Ethylene
The chief precursor of ethylene is the sulphur containing amino acid methionine.

12. Biosynthesis of Ethylene
1) Pathway of ethylene synthesis is given by Yang 1980
2) The amino acid methionine is precursor of ethylene and ACC
(1-aminocyclopropane - 1 carboxylic acid ) serves as an
intermediate between methionine and ethylene.
3) When methionine is conjugated with adenosine gives rise to
SAM (S - adenosyl methionine) in presence of enzyme
adomate synthetas and it used a molecule of ATP .
4) SAM in presence of amynocyclopropane carboxylic acid
synthetas (ACC synthetase) break down into
amynocyclopropane carboxylic acid and s -
methylthioadenosine .
5) Aminocyclopropane finally converted into ethylene in
presence of ACC oxidase.
• Precursor - Methionine

13. Cont…….
• Adam and Yang (1977) have worked out the
pathway for the biosynthesis of ethylene from
amino acid methionine.
• Methionine is activatedv by ATP to give rise to S-
adenosilmethionine (SAM)in the presence of an
enzyme methionine adenosyl transferase.
o The compound SAM in presence of enzyme ACC
synthetase break into S-Methelthioadenosine
(MTA) and aminocyclopropane carboxylic acid
(ACC).
ACC is finely converted into ethylene.
o This reaction is presumed to be triggered by
ethylene forming enzyme( EFE).

14. OUTLINE OF SYNTHESIS
OF ETHYLENE

15. CH3-S-CH2-CH2-CH(NH2)-COOH
(Methionine)
CH3-S-CH2-CH2-CHO
Methanol
CH3-S-CH2-CH2-CO-COOH
4-Methyl mercepto-2-oxo butyric
acid
CH2=CH2
ETHYLENE
FMN+Light
Transminase
Peroxidase +H202Peroxidase +H202

16. Transport
• In comparison to ACC synthase and ACC
oxide, less is known about ethylene perception
and single transduction, because of difficulties
in isolation and purifying ethylene.
• Ethylene released by tissue and diffuses in the
form of gas through intracellular space .
• Transport by diffusion.

17. Mechanism of ethylene action
Membrane permeability –
• Ethylene acts by changing permeability of the cell
membrane.
• Ethylene is lipid soluble, hence it gets dissolved in lipid
membrane and alters the permeability of membrane.
Nucleic acid and protein metabolism - Some responses
like fruit ripening & abscission are due to gene
expression and protein synthesis. Synthesises specific
mRNA and enzymes.
Regulation of auxin metabolism – Reduces biosynthesis
of auxins and inhibits its transport.

18. MECHANISM OF ACTION
• Increased permeability increases RNA and Protein
synthesis.
• It also accelerates the secretion of variety of enzymes
like polygalactourinase, cellulase and phospholipases
they cause softening and degradation of cell wall.
• α-amylase enzyme it results in hydrolysis of starch into
sugars.
• High permeability increases respiration thereby hastens
fruit ripening process.

19. ELIMINATING SOURCES OF ETHYLENE
• Specific anti-ethylene compounds: STS,
I-MCP
• Inhibition of ethylene biosynthesis:
AVG and AOA
• Activated or brominated charcoal
• Catalytic oxidizers: Platinized asbestos
• Chemical removal: KMnO4 (Purafil)

20. Anti-ethylene
• Ethylene is used commercially to ripen tomatoes,
bananas, pears and a few other fruits. Ethylene gas
is used to do this and it is a postharvest use.
• There are commercial liquid products that release
ethylene..
• These are only used preharvest. There are several
anti-ethylene chemicals. Silver thiosulfate (STS) is
used on flowers. AVG (trade name ReTainTM) blocks
ethylene synthesis.

21. • It is a liquid that is applied preharvest. The fruit
(plant) will not produce much ethylene, so there is not
an ethylene response. However, the plant can respond
to ethylene from another source.
• In contrast, 1-MCP blocks ethylene binding to its
receptor. It is applied postharvest. The fruit (plant)
may still produce some ethylene but there is no
response to any ethylene, regardless of source.

22. References
 Textbook of plant physiology – V. Verma
 Plant physiology – S.N.Pandy and B.K.Sinha
 Internet website www.plant physiol.org
www.plant cell
 Internet www.cab direct.

23. Thank you