ethylene, and it

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ethylene, and its role in fruit ripening

• 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,on tissue level and
  molecular aspects
• CURRENT APPLICATIONS

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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 evokes
  endosperm development and embryogenesis

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fruit defined..

• AFTER FERTILIZATION
• transforming of ovule into seed
• the ovary increases in size and undergoes a
  variety of morphological, anatomical and
  biochemical changes leading to formation of fruit
  with enclosed seeds

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ripe fruit

• as a process, the term fruit ripening is
  misleading
• ripening is the final stage of fruit development
• changes in biochemical pathway that are studied
• respiration, ethylene output, cartenoid
  synthesis, chlorophyll degradation, production of
  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 to this
  later)

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ethylene plays a active role in..

• shoot and root growth and differentiation
  (triple response)
• dormancy
• adventitious root formation.
• stimulates leaf and fruit abscission.

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ethylene plays a active role in..

• flower induction.
• stimulates flower opening.
• induction of femaleness in dioecious flowers.
• flower and leaf senescence.
• fruit ripening.

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the discovery of ethylene

• ancient Egyptians
• ancient Chinese
• 1864 the gas lamps
• 1901 Dimitry Neljubow
• 1917 Doubt
• 1934 Gane
• 1935 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 (MET) enzyme AdoMet synthetase
  S-Adenosyl-methionine (Ado-Met)
• 2. AdoMet ACC syththase 1-Aminocyclopropane-1-
  carboxylic acid (ACC)
• 3. ACC ACC oxidase ethylene

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signals to ethylene production

• ripening signals are a burst of ethylene
  production
• a wound, picking fruit, infection of bacteria or
  fungi all will initiate the production

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responses to ethylene

• Ethylene production or exposure to exogenous
  ethylene initiates different responses in
  different fruit.
• There are two types of fruit
• Climateric and non-climateric
• Climateric fruit show a large increase in
  ethylene production at the onset of ripening.
  After ripening ethylene output reaches a peak and
  continues at a high level through ripening

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responses to ethylene

• climateric fruit also respond to exogenous
  ethylene and causes the ethylene production to
  increase and advances the respiratory climateric
  in the fruits
• examples of climateric fruit are bananas, apples
  and pears
• non-climateric fruit do not produce ethylene
  during ripening process but respond to exogenous
  and also causes respiratory rate to increase. It
  does not promote natural ripening of these
  fruits.
• examples of non-climateric fruit are citrus and
  different berries such as strawberries

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ethylene transport

• Ethylene transport within the plant
• Ethylene is released by the tissues diffuses
  in the gas phase through intracellular spaces
  outside the tissues
• Ethylene transport within the fruit
• In comparison to ACC synthase and ACC oxidase,
  less is known about ethylene perception and
  signal transduction, 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 pigments
  surface, red, yellow or blue
• 2. Acids are broken down
• fruit changes from sour to neutral to sweet

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the ripening of fruit cont

• 3. Amylase degrades starch to sugar, hence the
  mealy quality to juiciness
• 4. The breakdown of pectin between the fruit
  cells unglues them so they can slip past each
  other, hence the softer fruit

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the ripening of fruit cont

• 5. Breakdown of large organic molecules to a
  variety of type and quantity of small volatile
  molecules that produce the aroma and tastes we
  associate with ripe fruit

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fruit ripening at molecular level

• changes in mRNA subsets
• include new gene transcription in mature fruit,
• a decrease in other transcriptions with advancing
  maturity of fruits
• disappearance of certain mRNAs in overripened
  fruits
• in some more detailactivities of cellulases,
  PG and PME

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fruit ripening at molecular level

• cellulases are enzymes normally functioning in
  cell walls causing breakdown of cellulose and
  hemicellulose
• PME and polygalacturonase (PG) causing pectin
  degradation
• above mentioned have led to characterization of
  genes

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fruit ripening at molecular level

• psbA, transcription in the chromoplasts which is
  at least 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 the
  middle 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

• Use of 1-MCP as a tool to investigate whether
  exogenous ethylene binds to the receptor to
  induce the respiratory rise and to affect
  ripening in strawberry fruit
• Use of cyclohexamide as protein inhibitor to test
  whether the ethylene effects are the result of
  new protein synthesis. Changes in ionic
  conductivity and peroxidase activity in ethylene
  treated strawberries were measured as markers

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conclusions in research

• Ethylene induced ionic leakage and associated
  water loss and peroxidase activity
• Results suggest that non-climateric fruit may
  have different ethylene receptors and/or ethylene
  receptors may have different regulatory functions

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current applications

• carbon application
• increasing shelf life of fruit
• Ethylene controlled environ-ments

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Thank you I hope you have a juicy summer