Ethylene is a plant hormone with the formula C2H4. It serves to stimulate or regulate fruit ripening, flower opening, and leaf shedding in plants. Ethylene was first discovered in 1864 to cause abnormal plant growth when released from street lamps. It has since been shown to induce various responses in plants like seed germination, fruit ripening, growth inhibition, abscission, flowering, and formation of adventitious roots and root hairs. Ethylene is biosynthesized from methionine and its effects are mediated by binding to a receptor and modulating gene expression.

2. INTRODUCTION
• Ethylene (IUPAC name: ethene) is a Hydrocarbon which has the
formula C2H4 or H2C=CH2. It is a colourless flammable gas with a faint
"sweet and musky" odour when pure. It is the simplest alkene.
• Ethylene serves as a hormone in plants. It acts at trace levels throughout the
life of the plant by stimulating or regulating the ripening of fruit, the
opening of flower, and the abscission(or shedding) of leaves. Commercial
ripening rooms use "catalytic generators" to make ethylene gas from a liquid
supply of ethanol. Typically, a gassing level of 500 to 2,000 ppm is used, for
24 to 48 hours.

3. HISTORY OF ETHYLENE
• In 1864, it was discovered that gas leaks from street lights led to stunting of
growth, twisting of plants, and abnormal thickening of stems
• Dimitry N. Neljubow (1901)(A Russian scientist) was the first to show the
importance of ethylene present in illuminating coal gas as a growth regulator of
plants.
• It was mainly concerned with the application of smoke to induce flowering in
pineapple and ripens banana.
• The active component of smoke was shown to be ethylene by Croker and Knight
(1908)
• Ethylene has been used since the ancient Egyptians, who would gash figs in order
to stimulate ripening (wounding stimulates ethylene production by plant tissues).
The ancient Chinese would burn incence in closed rooms to enhance the ripening
of pears

4. CHEMISTRY OF ETHYLENE:
• Ethylene is unsaturated hydrocarbon. It
is colourless gas which is lighter than
air at room temperature and sparingly
soluble in water.
• Ethylene is flammable and highly
volatile
• Ethylene is readily absorbed by
potassium permanganate (KMnO4). The
latter is frequently used to remove
excess ethylene from the storage
chambers.

5. OCCURRENCE, DISTRIBUTION, AND
TRANSPORT OF ETHYLENE IN PLANT

6. BIOSYNTHESIS OF ETHYLENE
• Ethylene is derived from amino acid Methionine.
• A non-protein amino acid, 1-amino cyclopropane-l-carboxylic
acid (ACC) is an important intermediate and also immediate
precursor of ethylene biosynthesis

8. • Break seed and bud dormancy
The dormancy of many seeds such as cereals can be broken by application of
ethylene
Ethylene application increases the rate of germination
Ethylene treatment sometimes used to promote bud sprouting in potato and
other tubers
• Fruit ripening
It Stimulate fruit ripening. The hormone is now known to accelerate ripening of
fruits in most cases including banana, apple, tomato etc.
In apple, the softening of fruits increases with increase in ethylene concentration.

9. • Growth inhibition
Exogenous application of ethylene inhibits the plant growth.
In most dicots, growth of stem, root and leaves inhibited but the hormone
enhances radial growth as a result both stem and root swell in response to
ethylene
• Stimulate abscission
It induces abscission of leaves fruits and leaves.
The abscission increases with ethylene concentration
Exposing fruiting cotton plants to 0.5ppm ethylene causes 100% abscission
of young fruits and floral buds within 2 days. In this respect, it is believed
that initial effect of ethylene is to lower the auxin content

10. • Induce flowering
In most cases ethylene inhibits flowering but in pineapple, mango and
litchi it has stimulatory effect
Plants can be treated with ethylene directly or by using ethylene releasing
compound like etherel stimulate ethylene production
• Sex Expression
Ethylene stimulate femaleness in plant. Cucumber and melon normally
produce male flowers earlier than female flowers. Ethylene stimulate the
early production of female flowers in these crops.
• Plumular Hook Formation
In etiolated dicot seedlings, the plumular tip (i.e., shoot apex) is usually
bent like a hook. This hook shape is advantageous to seedling for
penetration through the soil, protecting the tender apical growing point
from being injured

11. • 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
• 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 (i.e.,
diageotropism)
Triple response effects of etiolated seedlings were the first to be related
to beginning of discovery of ethylene as natural plant growth hormone.

12. INHIBITOR OF ETHYLENE
• Aminoethoxy- vinylglycine(AVG).
• Aminooxyacetic acid(AOA)
• Silver ions
• Carbon dioxide at high concentration(5-10%)
• trans- cyclooctane
• 1-methylcyclopropene

13. MECHANISM OF ETHYLENE ACTION
• Binding of ethane to a
receptor
• Activation of one or more
single transduction
pathway.
• Modulation of gene
expression leading to
cellular response.
1. Ethylene Gas (C2H4), 2. Plasma Membrane, 3.
Receptor, 4. Endoplasmic Reticulum, 5. CTR1 6.
EIN2 7. EIN3, 8. DNA, 9. mRNA ,10. HIS1
Differentiation and Growth