1. Fruit Ripening and Ethylene
HORT 301: Plant Physiology
December 9th, 2009
Dr. Michael Van Oosten

2. Phytochrome: regulation of
Embryo and
Seed development
Fruit ripening
Cells and cell growth
Seed development
Seed germination
Genes and enzymes
Fertilization and embryogenesis
Flowering
Skotomorphogenesis
Biotic stress
Abiotic stress
Phloem translocation
Water transport
Photomorphogenesis
Mineral nutrition
Photoreceptors
Nitrogen fixation
Phytochrome
Secondary metabolism
Primary metabolism
Phytochrome: regulation of
light responses
Respiration
Photosynthesis: light reaction
Photorespiration
Plant life cycle
Photosynthesis: carbon fixation

4. What Defines a Fruit? A fruit is a ripened ovary
A seed is a ripened ovule

5. Fruit forms in higher angiosperms

6. The Ripening Process Process of becoming edible Fruit becomes sweeter
(accumulation of sugars)
Fruit becomes softer
(more palatable)
Fruit becomes less green
(accumulation of pigments/decrease of chlorophyll)
Fruit generally becomes more acidic

7. Fruit ripening Partial digestion of cell walls and middle lamella
Degradation of chlorophyll and starch
Synthesis of anthocyanins and carotinoids
Respiration of organic acids
PP22110.jpg 7

8. Respiration and Ripening
Normally when a tissue reaches maturity, respiration rates drop off
Climacteric fruits show a rise in respiration during onset of ripening
Apples, Bananas, Aavocados
Climacteric ripening is triggered by Ethylene
Nonclimacteric do have a ethylene/respiration rise
Oranges, Grapes, Strawberries

9. Ethylene during ripening process
PP22110.jpg 9

10. Changes in the Cell Wall
Much of the cell wall is degraded
Expansins are produced to “loosen” cell wall
Middle lamella can be selectively degrade to allow cells to become “unglued” from each other

11. Ethylene AIR Ethylene effects Fruit ripening/ Senescence Abscission
Triple
response
Root hair
formation
AIR
Elongation
inhibiation
Increased
Radial growth
Pathogen defense
PP22110.jpg
Ethylene effects 11

12. Ethylene: it’s a gas!!
1864 illuminating gas powered street lights defoliate trees
1901 Russian Dimitry Neljubov identifies ethylene as phytohormone
1917 Doubt identifies ethylene as defoliant
1934 ethylene biosynthesis in plants detected
1935 ethylene is proposed as the “ripening hormone”
PP22110.jpg
Biologically active at less than 0.1ppm
Transported as ACC
Synthesized in ripening fruit and senescing tissues
Induced by auxin, draught, wounding, cold, stress,
fruit ripening, senescence, pathogen attack

13. Ethylene: it’s a gas!! H H C C H H
PP22110.jpg
Biologically active at less than 0.1ppm
Transported as ACC
Synthesized in ripening fruit and senescing tissues
Induced by auxin, draught, wounding, cold, stress,
fruit ripening, senescence, pathogen attack

14. Ethylene biosynthesis from methionine
SAM Synthetase
S-Adenosyl-Methionine
(SAM)
ACC-Synthase
NH3
COO-
H2C C +
1-Aminocyclopropan-
1-carbonic acid
(ACC)
PP22110.jpg O2
ACC-Oxidase
H2C
CH2
Ethylene 14

15. Ethylene mutations in tomato

16. Antisense-Inhibition of ACC-Oxidase
stops flower senescence

17. And Ethylene the defoliant….
Ethylene as a fruit ripening hormone
And Ethylene the defoliant….
PP22110.jpg 17

18. leaf
stem
Abscission zone at base of leaf at the where it joints the stem

19. Ethylene induces abscission
PP22090.jpg 19

20. Auxin prevents abscission
PP22110.jpg
However: unphysiological auxin concentrations have
herbicide effects (agent orange)

22. Phenotype of first gene is masked by phenotype of a second gene
Genetic epistasis
Phenotype of first gene is masked by phenotype of a second gene
etr1-3 ctr1-1
ein4-1 ctr1-1
etr2-1 ctr1-1
ein2-1 ctr1-1
ein3-1 ctr1-1
ein5-1 ctr1-1
constitutive triple response
ethylene insensitive
ETR1, EIN4, ETR2
PP22110.jpg
CTR1
EIN2, EIN3, EIN5

23. Ethylene Mutants Ethylene insensitive (EIN) Ethylene resistant (ETR)
Constitutive Triple Response (CTR)
Ethylene Response Sensor (ERS)
Ethylene Overproducer (ETO)

24. Ethylene: triple response
PP22110.jpg
Triple response:
- thickening of hypocotyl, radial growth
- reduction of cell elongation in hypocotyl and root
- exaggerated curvature of apical hook, reduced geotropism

25. Understanding the hormone: Searching for ethylene mutants (CTR1)
Wild-type
air
ethylene
air
ethylene
Recessive loss-of-function ctr1 mutations:
- Constitutive activation of ethylene response
- Ethylene induced genes are always “on”
- Constitutive triple response
CTR1 leads to inhibition of ethylene response
in absense of ethylene
PP22090.jpg
Constitutive triple
response
ctr1

26. Searching for ethylene mutants
Wild-type
Searching for ethylene mutants
Air
Ethylene
etr1
Ethylene resistant (exogenous ethylene added)
PP22090.jpg
Constitutive triple
Response (no exogenous ethylene)
ctr1

27. Understanding the hormone: Searching for ethylene mutants (ETR1)
Wild-type
Air
Ethylene
Air
Ethylene
PP22090.jpg
Etr (ethylene resistant)
Ein (ethylene insensitive)
etr1
Ethylene resistant
Ethylene receptors

28. Structure of ethylene receptors
GMP binding
PP22090.jpg

29. Understanding the hormone: Searching for ethylene mutants (ETO1)
Wild-type
Understanding the hormone: Searching for ethylene mutants (ETO1)
Air
Ethylene
- Ethylene overproducer show same phenotype as ctr1
- ctr1 not reversible by inhibitors of ethylene biosynthesis
- eto phenotype is reversed by ethylene synthesis inhibitors
ETO1 has de-regulated
ethylene biosynthesis
PP22090.jpg
Ethylene
overproducer
eto1 29

31. Horticultural Question
Why does blocking ethylene perception work much better than blocking ethylene production within the plant?

32. Ethylene and Horticulture
1-Methylcyclopropene 
Binds tightly to ethylene receptor and blocks activation
Marketed as:
EthylBloc (Flowers
SmartFresh
Apple
Kiwi
Tomatoes
Bananas
Plums
Avocados
Melons
INVINSA (drought & heat stress)
Corn
Soybeans
Cotton
Sunflower
PP22090.jpg