Plant growth regulators(Ethylene)

Plant Growth Regulators
Growth retardants (Ethylene)
Prof. Dr./ Galal Ismail Eliwa
Head Of Pomology Department
Faculty Of Agriculture
Damietta University
E. mail/ geliwa2002@du.edu.eg

Ethylene (C2H4 or CH2=CH2)
 Ethylene the only gaseous plant hormone (C2H4)
 This is a simple gas that is produced naturally in small
quantities by many plant tissues and is able to diffuse
readily, via intercellular spaces, throughout the entire plant
body.
 Ethylene is involved primarily in plant responses to
environmental stresses such as flooding and drought, and in
response to infection, wounding and mechanical pressure.
 It also influences a wide range of developmental processes,
including shoot elongation, flowering, seed germination,
fruit ripening and leaf abscission and senescence.
4/4/2020 Galal Eliwa 3

Ethylene (C2H4 or CH2=CH2)
It was difficult to fathom how
a two carbon compound
floating freely in the air could
be seriously considered to be
a hormone.

Discovery of Ethylene
Ethylene is an endogenous hormone.
 Ethylene has been used in practice since the
ancient Egyptians, who would gas figs in order
to stimulate ripening.
Gashing promotes ripening in figs
(4 days later)
Sycamore Fig
(‫جميز‬)

 He discovered that what was
causing the abnormal
morphology was the air in the
laboratory. It turns out that
the laboratory was using coal
gas (aka illuminating gas) for
lamp light. The active
ingredient in the air that
caused this growth response
was ethylene, a byproduct of
goal gas combustion.
 The growth regulation properties of ethylene were first
noted by Dimitry Neljubow in 1901 who reported that
leaf abscission could be stimulated by coal gas.
Discovery of Ethylene

Ethylene Biosynthesis
 Ethylene is produced in all higher plants and is
produced from methionine in essentially all
tissues.
 Production of ethylene varies with the type of
tissue, the plant species, and also the stage of
development.

Ethylene Biosynthesis
 The pathway starts with a
common amino acid,
methionine (MET), which is
energized by ATP to produce
S-adenosyl methionine (SAM)
 The key enzyme in the
pathway, ACC synthase,
converts SAM to 1-
aminocyclopropane-1-
carboxylic acid (ACC), the
immediate precursor of
ethylene.

Where Ethylene produced?
 Ethylene is the gaseous hormone that can be
produced by most all part of the plant.
 It produced in high concentrations during
senescence, leaf abscission, and the ripening
of some type of fruits.
 This hormone synthesis is also stimulated by
wounding & stress (drought, flooding,
mechanical pressure, injury, & infection).

Plants synthesize ethylene in response to stress
Drought stress Biotic stress Flooding
Heat stress Wounding
 Cold stress
 Osmotic stress
 UV stress
 Pathogen attack
 Mechanical stress

Ethylene Action
•1- Causes horizontal growth of seedling, swelling
of axis & apical hook formation in dicot seedling.
(Neljubow in 1901)

Ethylene Action
2- Ethylene- fruit ripening
 Under natural conditions, fruits undergo a series of
changes, including changes in color, declines in organic
acid content and increases in sugar content.
 In many fruits, these metabolic processes often coincide
with a period of increased respiration, the respiratory
climacteric.
 During the climacteric there is also a dramatic increase in
ethylene production.
 Ethylene initiate the climacteric in a number of fruits and
is used commercially to ripen tomatoes, avocados,
melons, kiwi fruit and banana.

What Makes Fruit Ripen?

Mechanism of ripening

Exposure of climacteric
fruits to ethylene
advanced the onset of
irreversible rise in
respiration rate and
rapid ripening.
Climacteric (Ethylene producing) Non-climacteric (Non ethylene producing)
Fruits: apple, apricot, avocado, pear,
peach, plum, mango, banana, papaya,
guava, sapota, kiwifruit, passion fruit,
jack fruit, persimmon
Fruits: Cherry, blackberry, strawberry,
citrus fruits (lime, lemon, orange, grape
fruit, mandarin), dates, grapes, loquat,
pomegranate, pineapple, raspberry
Vegetables: Tomato, muskmelon Vegetables: Eggplant, cucumber, okra,
pea, bell pepper, summer squash,
watermelon, leafy vegetables

Ethylene in ripening rooms

Ethylene in ripening
 The bananas you get from the store have usually been
gassed with ethylene already, so their climacteric is already
underway and they will ripen quickly after you get them out
of the store.
 Putting them in the refrigerator helps slow this process, but
it also turns the skin a dark brown.

Removal astringency from persimmon fruit with
alcohol: Fruit are packed into cardboard cartons
before being treated (Kitagawa 1970).

Removal astringency from persimmon fruit with
alcohol whilst fruit is on the tree:
individual fruit are enclosed in polyethylene
bags containing a little alcohol.
The bags are left in place for about 3 days.

Apple slices inducing ripening of persimmons
8 days in
bag with
apple
slices
Controls,
8 days
outside
of bag

“one bad apple spoils the whole bunch”
Pathway of Ethylene Biosynthesis

When the key enzyme of ethylene synthesis, ACC
synthase, was removed from tomato fruits using
molecular techniques, the fruits no longer ripened
unless they were treated with ethylene gas

Ethylene during flowering and fruit ripening
Ethylene was first detected as flower buds opened and exhibited
oscillations with peak production prior to petal abscission. After
that C2H4 production fells to a low and relatively continuous level
until fruit had entered the latter stages of being non-expanded and
dark-green

Once fruit initiated red coloration, C2H4 release becomes
elevated in a linear fashion (without diurnal fluctuations).

Ethylene Action
3- Ethylene- 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

Ethylene Action
• 4- Ethylene- Flower senescence
 Ethylene also promotes flower senescence
(ageing) in plants such as petunias,
carnations and peas.
Negative effects of ethylene
 Dropping of buds, flowers and
leaves (moulting)
 Accelerated ripening/ageing
(shrinking)
 Leaf yellowing, curved growth
(horizontal shipping)

Ethylene Action
• 5- Ethylene- leaf senescence
 The leaf senescence process is the same process
used for fruit ripening.
 The hypothesis you tested in lab was that auxin
produced at low concentration by a blade and/or
cytokinins coming up from the roots maintain the
integrity (similar to fruit hardness) of the leaf.
 Its color is green and the abscission zone (where the
petiole attaches to the stem) is composed of cells
glued firmly together with pectins.
 But when the days get short (nights get long!) and
the nights are much colder than the days, the plant
initiates senescence. Ethylene production stimulates
respiration and the gene expression for enzymes.

 These enzymes degrade chlorophyll and the Magnesium and
Nitrogen and Phosphorus are loaded into the phloem and
put into the trunk of the trees for winter. Cheap pigments
(hydrocarbons mostly) such as anthocyanin and carotenoids
are left in the leaf.
 It is also true that leaf senescence in the autumn is repeated
in the leaf petiole to lead to leaf abscission. This too is just
another example of the senescence protocol. However, it is
magnified in a layer of cells at the base of the petiole.
 These cells are signaled by ethylene, their respiration rises,
they produce enzymes including pectinase, the pectinase
unglues the cells in the abscission zone, and the leaf falls
from the tree. This zone of specially-responding cells is called
the abscission zone.

• 5- Ethylene- leaf senescence

Ethylene Action
• Although it is known that a
reduction of ethylene production
in female floral meristem that
is provoked by external
treatments with AVG or STS
causes a partial transformation
of female flowers into
hermaphrodite flowers.
6- Ethylene in: Family Cucurbitaceae
 Ethylene is involved in the sex determination in monoecious
members of the cucumber family. High [gibberellin] leads to
maleness, and high [ethylene] leads to femaleness.

Ethylene Action
• 7- Ethylene- Degreening of oranges, lemons and
grapefruit: Lemon growers would store newly
harvested green lemons in sheds kept warm by
kerosene stoves until they turned yellow and ripened
enough to market.
 Ethylene gas breaks down chlorophyll and lets colors
show through. (with ethylene at 1.5 ppm)

Ethylene Action
• 8- Ethylene- The Triple Response:
The change in growth form in
response to a mechanical
stimulation such as touch.
 Causes elongation of internodes
of deep-water rice plants, helping
the upper part to remain above
the water level.

METHODS FOR ARTIFICIAL RIPENING
1- Use of Calcium Carbide:
Calcium carbide (commonly known as
‟Masala”), a grayish solid, is readily produced
by heating calcium oxide with charcoal
under reducing conditions. When hydrolyzed,
calcium carbide produces acetylene,
containing trace amounts of ethylene that
are sufficient to be used in fruit ripening.

2- Ethephon (2-chloroethylphosphonic acid)
Ethylene-releasing agent was also identified as a
very effective growth retardant in the 1960s but
its use on bearing trees was limited because it
was also a strong fruit thinner (Edgerton and
Greenhalgh, 1969).
Ethephon is commercially available (Ethrel,
Florel, cepa) and used for enhancing
postharvest ripening.

Approved Uses for Ethephon in US Agriculture.
Use Approved crops (* Approved in some states of USA)
Post-harvest fruit ripening Bananas, tomatoes*
Pre-harvest fruit ripening Peppers, tomatoes
Fruit removal Apples, carob, crabapples, olive
Defoliation Apples, buckhorn, cotton, roses
Fruit loosening Apples, blackberries*, cantaloupes, cherries*,
tangerines
Maturity or colour
development
Apples, cranberries*, figs*, grapes, peppers,
pineapple, tomatoes
De-greening (preharvest) Tangerines, lemons
Dehiscence walnuts
Flower induction Pineapple and other bromeliads
Sex expression Cucumber, squash

Ethephon application converts male
flowers to female flowers in muskmelon

3- Use of Ethylene Gas
 In this technique, the fruits are exposed to low level of ethylene
gas (10–100 ppm) in an air-tight ripening chamber for 24 to 72
hours so as to induce ripening.
 Air-tight rooms should be opened and completely aired at 12
hour interval to prevent accumulation of carbon dioxide,
which reduces the effectiveness of ethylene.
 The most important thing in this technique is temperature
and relative humidity control inside the ripening chamber,
which should range between 18–25°C and 90–95% relative
humidity, depending upon the fruit kind and maturity
stage carbon dioxide concentration should be less than
4% air circulation should be sufficient to ensure
distribution of ethylene within ripening room.

The Ethylene Biosynthesis Inhibitor
• aminoethoxyvinylglycine (AVG) was recognized as
having stop drop capabilities in 1978 (Bangerth,
1978) but it was not developed for this purpose
because daminozide was a very acceptable
compound, it possessed several additional assets
and an economical way was not known to produce
this product and be competitively priced.
• AVG was registered as a drop control compound on
apples. It remains today as the prominent drop
control PBR.

The ethylene biosynthesis inhibitor
The most recent candidate as a drop control PBR
is 1-methylcyclopropene (1-MCP) (Yuan and
Carbaugh, 2007). This is a compound that is
released as a gas which then binds irreversibly to
ethylene binding sites within the plant. It was
first used in the mid 1990s to extend the
postharvest life of ornamentals.

Negative effects of ethylene
 Dropping of buds, flowers and leaves
(moulting)
 Accelerated ripening/ageing
(shrinking)
 Leaf yellowing, curved growth
(horizontal shipping)
Growers’ treatment products which
have a base of silver thiosulphate/STS
(Chrysal AVB) or 1-MCP (Chrysal
Ethylene Buster), protect against the
above mentioned negative effects of
increased ethylene production
(internal and external)

silver thiosulphate/STS
For cut flowers it is possible to pulse the stems with a
solution of silver thiosulfate. The flowers take the
solution up through their stems and this protects them
from the effects of ethylene.

Physiological effects of ethylene
1. Fruit
Ripening
Ethylene in the form of gas helps ripens
fruits under natural conditions.
2. Flower
Initiation
Ethrel (Ethephon) and ACC promote
flower initiation in pineapple
3. Leaf and
Fruit
Abscission
Accelerates fruit abscission for
mechanical harvesting in fruit crops
such as grapes, cherries and citrus.
4. Inhibit
Vegetative
Growth
Ethephon may be used for inhibiting
vegetative growth of grape vines
resulting in higher yield and better
quality.

Thank you four your attention

Plant growth regulators(Ethylene)

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