ethylene the ripening hormone

8/14/2019 Ethylene the Ripening Hormone

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ETHYLENETHYLENETHE RIPENING HORMONEHE RIPENING HORMONE


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Ethylene Facts

Ethylene is a natural plant hormone.It affects the growth, development, ripening,and senescence (aging) of all plants. It isnormally produced in small quantities by most

fruits and vegetables. Many fruits producelarger quantities of ethylene and respond withuniform ripening when exposed to an externalsource of ethylene.


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Ethylene has been found not harmful or toxic tohumans in the concentrations found in ripeningrooms.

In fact, ethylene was used medically as a anesthetic inconcentrations significantly greater than that found ina ripening room. However, ethylene is often targetedas the reason for difficulty in breathing in ripeningrooms; what can affect some people is usually either:

a) Carbon Dioxide (CO2,) levels: CO2, is produced bythe ripening fruit in the room and levels increase overtime, orb) Oxygen levels: The oxygen in the room whenloaded is taken in by the ripening fruit. This sometimeswill make breathing in a ripening room difficult. Theincreased CO2, and decreased oxygen levels are the

main reasons for venting the ripening room.


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Ethylene action slows at lower temperatures.At their minimum temperature levels, fruit is basicallyinactive and does not respond well to externallysupplied ethylene.

Ethylene will penetrate most substances.In fact, it will permeate through produce cardboardshipping boxes, wood and even concrete walls.


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Ethylene is harmful to many fruits, vegetables, and floralitems.While ethylene is invaluable due to its ability to initiate theripening process in several fruits, it can also be veryharmful to many fruits, vegetables, flowers, and plants byaccelerating the aging process and decreasing the productquality and shelf life. The degree of damage depends uponthe concentration of ethylene, length of exposure time, andproduct temperature. One of the following methods should

be used to ensure that ethylene-sensitive produce is notexposed:

Ethylene producing items (such as apples, avocados,bananas, melons, peaches, pears, and tomatoes) shouldbe stored separately from ethylene-sensitive ones (broccoli,

cabbage, cauliflower, leafy greens, lettuce, etc.). Also,ethylene is emitted by engines. Propane, diesel, andgasoline powered engines all produce ethylene in amountslarge enough to cause damage to the ethylene-sensitiveproduce items mentioned;


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Ventilate the storage area, preferably to the outside ofthe warehouse, on a continuous or regular basis to

purge the air of any ethylene; Remove ethylene with ethylene absorbing filters.

These have been proven in reducing andmaintaining low ethylene levels. If ethylene damage

is suspected, a quick and easy way to detectethylene levels is with hand held sensor tubes. Thiswill indicate if the above steps should be followed.


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FUNCTIONS OF ETHYLENE

Stimulates the release of dormancy.

Stimulates shoot and root growth and differentiation (triple response)

May have a role in adventitious root formation.

Stimulates leaf and fruit abscission.

Stimulates Bromiliad flower induction.

Induction of femaleness in dioecious flowers.

Stimulates flower opening.

Stimulates flower and leaf senescence.


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ETHYLENE


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Ethylene is a small hydrocarbon gas. It is naturally occurring, but it canalso occur as a result of combustion and other processes. You can'tsee or smell it. Some fruit will produce ethylene as ripening begins.

Apples and pears are examples of fruit that produce ethylene withripening. Ethylene is responsible for the changes in texture, softening,color, and other processes involved in ripening. Fruits such as cherriesand blueberries do not produce much ethylene and it doesn't influencetheir ripening.


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Ethylene is thought of as the aging hormone in plants. In additionto causing fruit to ripen, it can cause plants to die. It can be

produced when plants are injured, either mechanically or bydisease. Ethylene will cause a wide range of effects in plants,depending on the age of the plant and how sensitive the plant isto ethylene. Ethylene effects include fruit ripening, loss ofchlorophyll, abortion of plant parts, stem shortening, abscissionof plant parts, and epinasty (bending of stems). Ethylene can be

either good or bad, depending on what commodity you work with.It is used in a positive manner in fruit ripening, for example. It canalso cause damage in crops. Examples of damage might includeyellowing of vegetables, bud damage in dormant nursery stock,or abscission in ornamentals (leaves, flowers drop off). Often two

of the important items to know are 1) if a crop naturally producesa lot of ethylene and 2) if it is responsive to ethylene.Responsiveness will depend on 1) the crop, 2) the stage of plantdevelopment, 3) the temperature, 4) the concentration ofethylene, and 5) the duration of exposure.


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Ethylene gas is used commercially to ripen tomatoes,bananas, pears, and a few other fruits postharvest. Ethylenecan be explosive if it reaches high concentrations, so it hasto be used cautiously. Several commercial liquid productsrelease ethylene (ethephon, trade name Ethrel). These areonly used preharvest. There are three main ways to produce

ethylene: 1) gas from a cylinder, 2) catalytic generator, and 3)ethephon. Other sources of ethylene include ripening fruit,exhaust from internal combustion engines/heaters, smoke(including cigarettes), welding, rotting vegetation, natural gasleaks, and manufacturing plants of some kinds.


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Respiration is significant during all stages of fruit.maturation Fruit

, ( )cells are alive so they need to consume food mostly sugar tomaintain

. ,their own life processes Through cellular respiration one sugar

( )molecule either glucose or fructose reacts with six oxygen

moleculesto produce six molecules of water and six molecules of carbon

,dioxide.plus 670 kcal of energy

( ) + ( ) ( ) + ( ) +C6H12O6 aq 6O2 g 6CO2 g 6H2O l 670 kcal

,This respiration process involves many intermediates stepswhich

,create other chemical compounds important to the softening,coloring

, .flavor and odor of the fruit Plant physiologists can monitor

respiration .by measuring the amount of CO2 gas the fruit produces For many,fruits respiration is high during the first stage of

,development declines,during the second stage and then rises sharply at the start of

the third

.stage This sharp rise is called the .climacteric

ETHYLENE AND ITS EFFECT ON RESPIRATION


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,ot all plants exhibit the climacteric but those that do produce.thylene at the same time This time of peak respiration signals the end

.f the fruit s life Chlorophyll disappears and other colors that were.asked by chlorophyll begin to show through Apples start to look red. ,nd bananas turn yellow If an apple is bruised or damaged it produces

, .xtra ethylene and other apples nearby spoil rapidly Scientists foundhat folklore was right one rotten apple can .spoil the whole barrel

, , itrus plants among others don t go through a climacteric at the.nd of the third stage of development These plants have no abrupt

hange but show a steady decline in respiration from the first stage. , ,hrough the fourth However if citrus fruits are exposed to ethylene

hey show a sharp rise in respiration and go through an induced. .limacteric Some of the ripening changes accelerate The most

,onspicuous change is the disappearance of chlorophyll which is whyhe grocer s lemons looked ripe after he placed them near the kerosene

. , ,tove For citrus however this accelerated ripening is more appearance. ,han substance The steady ripening of the fruit as measured by sugar, .ontent is not increased when the skin changes color Often the fruit is

. ,dible and sweet well before the chlorophyll disappears Just the sameost customers prefer yellow lemons and orange oranges


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, ,or fruits like bananas which go through a climacteric ethylene can.be used to trigger the normal ripening of green fruit Bananas are

, , , ,grown in the tropics and when ripened naturally are yellow soft, .sweet and highly perishable It is disastrous to pick and ship ripe. ,nanas Plant respiration is a chemical process and if the bananas are

( )kept cool but not below 12 C respiration proceeds slowly and the.bananas stay green and hard for a long time When the bananas reach

, .ir destination a quick exposure to ethylene triggers the climacteric

. Within a few days the fruit is ripe and tasty

Plant physiologists have also discovered how to suppress the effect , .f a fruit s own ethylene thus postponing ripening and rotting Apples

.are harvested in the fall and normally stay fresh for a few weeks,However when they are stored at low temperatures and the carbon

,xide in the surrounding air is increased slightly the apples are less.sensitive to their own naturally produced ethylene This controlledorage slows the aging process and has made it possible for us to buy

, . ,irm fresh apples all year long Unfortunately the stored apples lose,e of the chemicals responsible for their flavor so they look and feel

- .good but lack the fresh taste of just picked apples


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THE END

ethylene the ripening hormone

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