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