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ethylene, and it¶s role in fruitripening

Sarah Minnery

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~ a tribute to summer~

«.& locally grown seasonal fruit

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Outline

FRUIT defined

RIPE FRUIT defined ETHYLENE, the plant hormone ETHYLENE & RIPENING of FRUIT,ontissue level and molecular aspectsCURRENT APPLICATI O NS

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Fruit defined..

fruit is a mature ovary of the flower the wall of the ovary in the fruit is known as

the pericarp, becomes differenetiated into ± 1.outer exocarp ± 2.middle mesocarp ± 3.inner endocarp

dlb fertilization is the trigger that evokesendosperm development and embryogenesis

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fruit defined.. AFTER FERTILIZATION«««

transforming of ovule into seedthe ovary increases in size and undergoes avariety of morphological, anatomical and

biochemical changes leading to formationof fruit with enclosed seeds

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ripe fruit as a process, the term µfruit ripening¶ ismisleadingripening is the final stage of fruitdevelopmentchanges in biochemical pathway that arestudied; ± respiration, ethylene output, cartenoid

synthesis, chlorophyll degradation, productionof cell wall hydrolases and softening process

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ripe fruit ripening is a differentiating process

± fruit have an increase in protein content ± fruit retain the capacity to synthesize proteins &

RNA

± inhibitors of protein & RNA synthesis prevent

the process of ripening ( I will come back tothis later)

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ethylene plays a active role in..1. shoot and root growth anddifferentiation (triple response)2. dormancy3.adventitious root formation.4.stimulates leaf and fruit abscission.

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ethylene plays a active role in..5 . flower induction.6. stimulates flower opening.7. induction of femaleness in dioecious

flowers.8. flower and leaf senescence.

9. fruit ripening.

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the discovery of ethyleneancient E gyptiansancient Chinese1864; the gas lamps1901; Dimitry N eljubow

1917; Doubt1934; Gane193 5 ; Crocker

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the discovery of ethylene

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biosynthesis and metabolism Produced in all higher plants produced from methionine in essentially all

tissues products of ethylene depend on type of tissue, the plant species, and the stage of

developement

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biosynthesis and metabolism ± 1. Methionine (M ET ) + enzyme A doMet

synthetase = S- A denosyl-methionine ( A do-Met)

± 2. A doMet + A CC syththase = 1-A minocyclopropane-1-carboxylic acid ( A CC)

± 3. A CC + A CC oxidase = ethylene

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signals to ethylene productionripening signals are a burst of ethylene

productiona wound, picking fruit, infection of bacteriaor fungi all will initiate the production

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responses to ethylene E thylene production or exposure to exogenousethylene initiates different responses indifferent fruit.

There are two types of fruitClimateric and non-climatericClimateric fruit show a large increase in ethylene

production at the onset of ripening. A fter ripeningethylene output reaches a peak and continues at ahigh level through ripening

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responses to ethyleneclimateric fruit also respond to exogenous ethylene andcauses the ethylene production to increase and advancesthe respiratory climateric in the fruitsexamples of climateric fruit are banana¶s, apples and

pearsnon-climateric fruit do not produce ethylene duringripening process but respond to exogenous and alsocauses respiratory rate to increase. I t does not promotenatural ripening of these fruits.examples of non-climateric fruit are citrus and different

berries such as strawberries

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ethylene transport E thylene transport within the plant ± E thylene is released by the tissues & diffuses in the gas

phase through intracellular spaces & outside the tissues

E thylene transport within the fruit ± In comparison to A CC synthase and A CC oxidase, less

is known about ethylene perception and signaltransduction, because of difficulties in isolating and

purifying ethylene receptors or ethylene binding proteins

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ethylene signals result in the

ripening of fruit 1.Chlorophyll is broken

down, new pigmentssurface, red, yellow or blue

2. A cids are broken downfruit changes from sour toneutral to sweet

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the ripening of fruit cont¶

3. A mylase degrades starchto sugar, hence the mealyquality to juiciness

4. T he breakdown of pectin between the fruit cellsunglues them so they can

slip past each other, hencethe softer fruit

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the ripening of fruit cont¶

5 . Breakdown of largeorganic molecules to a

variety of type andquantity of small volatilemolecules that producethe aroma and tastes weassociate with ripe fruit

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fruit ripening at molecular level changes in m RNA subsets ± include new gene transcription in mature fruit, ± a decrease in other transcriptions with

advancing maturity of fruits ± disappearance of certain m RNA ¶s in

overripened fruitsin some more detail ««« activities of cellulases, P G and P ME

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fruit ripening at molecular level cellulases are enzymes normallyfunctioning in cell walls causing breakdownof cellulose and hemicellulose

PME and polygalacturonase ( P G) causing pectin degradation

above mentioned have led tocharacterization of genes

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fruit ripening at molecular level psb A , transcription in the chromoplasts which is atleast 20 fold than the transcript level of other

photosynthetic genes in ripe fruit

PSY-phytoene synthase, 1st enzyme in cartenoid pathway

PME -enzyme causes pectin deformation of themiddle lamella of plant cell walls

± activity of enzyme inc. 2-3 fold during ripening PG, protein accumulates in pericarp first and

accounts for 3- 5% of soluble proteins ± 2000 fold inc. in mature ripe fruits

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current research U se of 1-MC P as a tool to investigate

whether exogenous ethylene binds tothe receptor to induce the respiratoryrise and to affect ripening in strawberryfruit

U se of cyclohexamide as proteininhibitor to test whether the ethyleneeffects are the result of new proteinsynthesis. Changes in ionicconductivity and peroxidase activity inethylene treated strawberries weremeasured as markers

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conclusions in research E thylene induced ionic leakage and

associated water loss and peroxidase

activity R esults suggest that non-climatericfruit may have different ethylenereceptors and/or ethylene receptorsmay have different regulatory functions

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current applicationscarbonapplication

increasingshelf life of fruit

E thylene

controlledenviron-ments

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Thank you& I hope

you have a juicy summer