Plant Growth Regulators Growth retardants (Ethylene)

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Plant Growth RegulatorsGrowth retardants
(Ethylene)

• Prof. Dr./ Galal Ismail Eliwa
• Head Of Pomology Department

Faculty Of Agriculture Damietta University
E. mail/ geliwa2002_at_du.edu.eg
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Ethylene (C2H4 or CH2CH2)

• 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.

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Ethylene (C2H4 or CH2CH2)
It was difficult to fathom how a two carbon
compound floating freely in the air could be
seriously considered to be a hormone.
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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.

Sycamore Fig(????)
Gashing promotes ripening in figs (4 days later)
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Discovery of Ethylene

• 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.

• 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.

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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.

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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.

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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).

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Plants synthesize ethylene in response to stress
Flooding
Biotic stress
Drought stress

• Cold stress
• Osmotic stress
• UV stress
• Pathogen attack
• Mechanical stress

Heat stress
Wounding
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Ethylene Action

• 1- Causes horizontal growth of seedling, swelling
  of axis  apical hook formation in dicot seedling.

(Neljubow in 1901)
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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.

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What Makes Fruit Ripen?
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Mechanism of ripening
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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
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Ethylene in ripening rooms
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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.

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Removal astringency from persimmon fruit with
alcohol Fruit are packed into cardboard cartons
before being treated (Kitagawa 1970).
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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.
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Apple slices inducing ripening of persimmons
8 days in bag with apple slices
Controls, 8 days outside of bag
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one bad apple spoils the whole bunch
Pathway of Ethylene Biosynthesis
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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
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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
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Once fruit initiated red coloration, C2H4 release
becomes elevated in a linear fashion (without
diurnal fluctuations).
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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

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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)

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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.

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• 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.

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• 5- Ethylene- leaf senescence

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Ethylene Action

• 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.

• 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.

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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)

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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.

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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.

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METHODS FOR ARTIFICIAL 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.

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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
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Ethephon application converts male flowers to
female flowers in muskmelon
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METHODS FOR ARTIFICIAL RIPENING

• 3- Use of Ethylene Gas
• In this technique, the fruits are exposed to low
  level of ethylene gas (10100 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 1825C and 9095 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.

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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.

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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.

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• 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)
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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.
silver thiosulphate/STS
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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.
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Thank you four your attention