L10 - Ethylene

Question 1

Sources of ethylene

Answer 1

(Concentration in outside air is generally low)

• outside air = 2ppb or 0,002 ppm to 10ppb or 0,01 ppm
• storage room = up to 1.000.000 ppb or 1000ppm

Main sources:

• PE plants
• Industrial pollution
• Cars and trucks

(Plants are also sources of ethylene)

Question 2

Classic 5 hormones

Answer 2

1. Ethylene
2. Auxin (IAA)
3. Absisic Acid (ABA)
4. Cytokinin (Zeatin)
5. Gibberellins - Gibberellic acid (GA3)

Question 3

What is a plant hormone

Answer 3

a. Have pronounced effects on biological processes already
at really low concentrations

b. Often pleiotropic effects (so also often unwanted side
effects)

c. Maybe also translocation in the organism
d. Clear dose response curves

e. Often hundreds to thousands of different genes are
activated/deactivated in response to hormones

Question 4

Role of ethylene

Answer 4

Ripening, senescence, abscission

Question 5

Role of cytokinins

Answer 5

anti senescence, especially in leafy materials

vegetables, flowers, potted

Question 6

Role of gibberellins

Answer 6

conserve green color (but may not

conserve photosynthetic activity!)

Question 7

Role of auxins

Answer 7

Determinant of maturity: as long as there is a lot
of auxin, the fruit will not be able to ripen (to respond to
ethylene). Auxins also antagonize the effect of ethylene
in abscission

Question 8

Role of ABA

Answer 8

may promote ethylene production, may trigger senescence in ethylene insensitive products, may limit transpiration, may increase chilling tolerance, may
stimulate ripening in ethylene insensitive products

examples:

1. Promotes anthocyanin biosynthesis and increased expression of flavonoid synthesis gens in table grapes
2. ABA triggers strawberry fruit ripening

Question 9

Hormones with no effects on postharvest quality

Answer 9

Salicylic acid, Jasmonic acid, polyamines and
NO have been found to affect postharvest quality

• Not many applications yet in commercial storage!
• The effects are often not that straight forward

Question 10

Potential role and effects of alternative hormones

Answer 10

(Methyl) jasmonate : May have a similar effect of
ethylene or may counteract ethylene
●stimulates ripening, color formation in many fruit.
Improves chilling tolerance, stress tolerance

(Methyl) salicylate:
Improves chilling tolerance, stimulates heath
production!

Polyamines:
may interfere with ethylene production, are
also antioxidants, may prolong shelf life

Nitric oxide (NO): Strong interaction with ethylene, may also act as antioxidant

Question 11

Inter-plant communication through ethylene is possible

Answer 11

Some hormones are “volatile” so that for instance in
storage or distribution products can stimulate each others
ripening/senescence

Question 12

Effect of ethylene in plants

Answer 12

● Ripening
● Senescence, over ripening (cell death)
● Abscission (leaves, flowers, fruit, ..)
● Yellowing (breakdown chlorophyll)
● Color synthesis (production anthocyanins, lycopene)
● Suppresses growth rate
● Developmental processes (flower formation, root
formation, ..)
● Stimulation of fungal infections

Question 13

Example of fruits were ethylene is INVOLVED in ripening

Answer 13

Ethylene
causes ripening but also deterioration
These fruit produce
their own ethylene

 apple
 pear
 mango
 tomato
 banana
 melon
 avocado

Question 14

Example of fruits were ethylene STIMULATES ripening

Answer 14

In such products ethylene is not required
for the ripening and is mostly negative for
product quality

 strawberry (and other berries)
 broccoli
 grapes
 bell pepper
 artichoke
 star fruit
 Cucumber ,
 Lettuce
 Lime, lemon, oranges

Question 15

Ethylene and flowers:

Sensitive - Intermediate - Insensitive

Answer 15

Sensitive:
● Carnation
● Campanula
● Trachelium
● Gypsophila
● Orchids
● Physostegia
● Scabiosa
● Petunia

Intermediate:
● Rose
● Snapdragon
● Aconitum
● Scabiosa
● Alstroemeria

Insensitive:
● Iris
● Chrysanthemum
● Euphorbia
● Gladiolus
● Liatris

Question 16

Ethylene treatments of horticultural products

to stimulate the ripening

Answer 16

• Ethylene gas
• Released from a soluble chemical ( ethephon ) with
  trade name Ethrel
• Produced from ethanol

Question 17

Other uses of ethylene

Answer 17

 Stimulate ripening of e.g.
● Avocado
●Mango
● Tomato (when harvested green)

But in these fruit, ethylene will not give satisfactory
results if fruit is harvested very unripe (unlike in
banana)

 Degreening of citrus fruit
 Growth inhibition in mung bean sprout production
 Fruit/leaf thinning

Question 18

Summary (Last slide)

Answer 18

 Some fruit need ethylene to ripen properly. Under
natural conditions the fruit will produce its own ethylene

 To stimulate ripening of unripe harvested fruit we can treat the fruit postharvest with ethylene

 Many fruit and vegetables do not need ethylene to become ripe and eatable. For these products exposure to ethylene is mostly negative for quality

 For flower and potted plants exposure to ethylene is mostly negative for quality