ethylene, and it’s role in fruit
ripening
Sarah Minnery
~a tribute to summer~
….& locally grown seasonal
fruit
Outline
• FRUIT defined
• RIPE FRUIT defined
• ETHYLENE, the plant hormone
• ETHYLENE & RIPENING of FRUIT,on
tissue level and molecular aspects
• CURRENT APPLICATIONS
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
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
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
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)
ethylene plays a active role in..
1. shoot and root growth and
differentiation (triple response)
2. dormancy
3.adventitious root formation.
4.stimulates leaf and fruit abscission.
ethylene plays a active role in..
7. flower induction.
8. stimulates flower opening.
9. induction of femaleness in dioecious
flowers.
10.flower and leaf senescence.
11. fruit ripening.
the discovery of ethylene
• ancient Egyptians
• ancient Chinese
• 1864; the gas lamps
• 1901; Dimitry Neljubow
• 1917; Doubt
• 1934; Gane
• 1935; Crocker
the discovery of ethylene
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
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
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
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
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 banana’s, 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
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
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
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
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
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 mRNA’s in
overripened fruits
• in some more detail………activities of
cellulases, PG and PME
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
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
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
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
current applications
• carbon
application
• increasing
shelf life of
fruit
• Ethylene
controlled
environ-
ments
Thank you
& I hope
you have a
juicy
summer
