Lecture 7 Ethylene

1
Lecture 7 - Ethylene

• Reference Taiz Zeiger (1998) Ch. 22
• Background to ethylene
• Ethylene synthesis transport
• Physiological effects of ethylene

2
Background to ethylene

• Historical
• ancient Chinese picked fruits ripen with
  incense.
• bonfires Puerto Rico, Phillipines promote
  flowering pineapples, mangoes.

3
Background to ethylene

• Historical cont.
• 1800s streets lit with ethylene lamps
• leaks caused defoliation of trees.

4
Background to ethylene

• Historical cont.
• Jamaican Ag. Dept
• store oranges bananas together.
• premature ripening bananas.

5
Background to ethylene

• Historical cont.
• 1901 Neljubov
• stems of pea seedlings grew slowly, thickly,
  horizontally
• leaf epicotyl hook opening retarded.

Taiz Zeiger (1998) Fig 22.4
6
Background to ethylene

• Historical cont.
• Gane et al. (1934)
• ethylene as natural plant product
• classified as hormone.

7
Background to ethylene

• Historical cont.
• not regarded as impt hormone (auxin)
• gas chromatography (1959)
• "rediscovered".

8
Ethylene synthesis transport

• Synthesis
• prod. all parts of seed plants.
• meristems, nodes
• levels rise senescence, abscission, ripening,
  wounding, stress.

9
Ethylene synthesis transport

• Synthesis
• from methionine
• simple structure
• lighter than air

Taiz Zeiger (1998) Fig 22.1
10
Ethylene synthesis transport

• Synthesis
• active low concn
• diffuse thru tissues
• fungi bacteria

11
Physiological effects of ethylene

• Fruit ripening
• fruit ripening
• degradation cell walls
• sugar accumulation
• disapp. phenolics
• -seeds ready for dispersal.

12
Physiological effects of ethylene

• Fruit ripening cont.
• accelerates ripening (many sp.)
• large inc. respiration some fruits (climacteric).

Taiz Zeiger (1998) Fig 22.5
13
Physiological effects of ethylene

• Fruit ripening - early 1900s.
• curing fruit in rooms with kerosene stove.
• small quantities of ethylene prod. enhanced
  ripening.

14
Physiological effects of ethylene

• Fruit ripening - current
• high conc (5-10) CO2 inhibits effects
• storage high CO2, low O2
• autostimulation synthesis.

15
Physiological effects of ethylene

• Leaf epinasty
• downward curving leaves
• adaxial petiole growth
• waterlogging of roots.

Taiz Zeiger (1998) Fig 22.4
16
Physiological effects of ethylene

• Lateral cell expansion
• reduction cell elongation
• lateral swelling
• common many plants.

Taiz Zeiger (1998) Fig 22.4
17
Physiological effects of ethylene

• Lateral cell expansion cont.
• longitudinal orientation MT's
• reorientation microfibrils
• transverse growth.

Taiz Zeiger (1998) Fig 15.17
18
Physiological effects of ethylene

• Seed bud dormancy
• breaks seed dormancy (cereals)
• inc germination
• breaks bud dormancy e.g. potato

19
Physiological effects of ethylene

• Elongation in aquatic sp.
• promotes stem, petiole expansion
• allows leaves to stay above water
• GA inv. (rice).

20
Physiological effects of ethylene

• Root root hair growth
• high concns adventitious roots
• root hair inc. Arabidopsis

Taiz Zeiger (1998) Fig 22.4
21
Physiological effects of ethylene

• Flower induction
• inhibits most sp.
• pineapple, mango
• synchroniz. fruit set.

22
Physiological effects of ethylene

• Sex expression
• promotion femaleness monoecious sp.
• cucumber
• high GA. male
• ethylene female.
• female buds produce more ethylene
• eg. squash, pumpkin, melon.

23
Physiological effects of ethylene

• Leaf senescence
• promotes loss chlorophyll
• ABA involved
• increases rate not developmental switch

24
Physiological effects of ethylene

• Ethylene abscission
• promotes abscission leaves, flowers, fruits.
• triggers cell wall degrading enzymes
• auxin a suppressant.

Taiz Zeiger (1998) Fig 22.8
25
Physiological effects of ethylene

• Ethylene aquatic plants
• gas channels (aerenchyma)
• ethylene-signalled cell death.

Taiz Zeiger (1998) Fig 25.15
26
Physiological effects of ethylene

• Mechanism of action
• alters gene expression
• ripening genes
• pathogenesis related genes.

Online Biology Book
27
Physiological effects of ethylene

• Ethephon
• discovered 1960's
• aqueous form taken up by plants
• slow release ethylene.

28
Physiological effects of ethylene

• Ethephon
• hastens fruit ripening
• degreen citrus fruit
• synchronise flowering/fruit set/fruit thinning.