Chapter 22 Ethylene: the gas hormone

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Chapter 22 Ethylene the gas hormone

• Discover
• coal gas was used for street illumination
• ? the serious defoliation of trees closing
  street-lamp
• lighter than air
• Symptoms
• triple response
• reduced stem elongation, increased lateral
  growth (swelling),
• abnormal and horizontal growth.
• The relationship between auxin synergism.
• Gas chromatography quantitative
• 5 parts per billion (ppb), 5 nL per liter.
• Laser-driven photoacoustic detector
• 50 parts per trillion (ppt), 0.05 nL per
  liter.

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Ethylene biosynthesis

• ? meristematic regions and nodal regions
• ? during leaf abscission and flower senescence,
  as well as during fruit ripening
• ? physiological stresses wounding, flooding,
  chilling, disease, temperature or drought, etc.
• ? Sources
• gymnosperms and lower plants, bacteria,
  fungi
• ? even marine sponge and cultured mammalian cells
  can respond to ethylene.
• ? the biologically active concentration 1?L L-1.

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? ? ? CO2 (p. 572) Absorbent alkaline KMnO4
Exogenous ACC, ethephon (p. 584)
Major Minor
GACC, 1-(?-L-glutamylamino) cyclopropane-1-carboxy
lic acid
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ACC synthase an unstable, low amounts
(0.0001), and cytosolic enzyme. a divergent
multigene family, at least nine genes in tomato,
which are regulated by various inducers,
such as auxin, wounding, and/or fruit ripening.
inhibitors aminoethoxy-vinyl-glycine (AVG),
aminooxyacetic acid (AOA),
inhibit the cofactor pyridoxal
phosphate, of ACC synthase. ACC oxidase
(ethylene forming enzyme) the rate-limiting
step in the ethylene biosynthesis. require
ferrous (Fe2) and ascorbate for activity. low
abundance and cofactors requirement ? difficult
purification. a multigene family that is
differentially activated by fruit ripening and
flower senescence, and inhibited by cobalt
ion (Co2) and anaerobiosis.
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Promote ethylene biosynthesis

• developmental state
• maturation application of ACC to unripe
  fruits.
• environmental conditions
• bio- and abiotic stress ethylene.
• plant hormones
• auxin
• auxin? ACC synthase ? ethylene
  production
• ? auxin-induced responses is mediated
  by ethylene.
• cytokinin
• promote ethylene production ?
  triple-response
• increase the stability and/or activity
  of one isoform of
• ACC synthase carboxy-terminal
  domain.
• cytokinin have synergistic influence on
  auxinsinduced ethylene production.
• circadian peaking during the day and reaching
  a minimum at night

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Inhibit ethylene production and action

• ? To distinguish between different hormones that
  have identical effects or
• a hormone affects the synthesis or action
  of another hormone
• auxin and ethylene causing epinasty
• ? ethylene is the primary effector of epinasty
  and auxin acts indirectly by
• causing a substantial increase in ethylene
  production.
• ? inhibitors of ethylene synthesis
• AVG, AOA, Co2
• ? inhibitors of ethylene action
• Silver ions (AgNO3 or Ag (S2O3)23-)
• carbon dioxide (510) antagonist, less
  efficient than silver ions.
• trans-cyclooctene
• 1-methylcyclopropene (MCP)
• ? remove ethylene
• alkaline potassium permanganate
• lysophospatidylethanolamine

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Ethylene affect development and physiology

• promotes the ripening of some fruits
• leaf epinasty
• induces lateral cell expansion
• maintains the hooks of dark-growing seedling
• break seed and bud dormancy in some species
  (abscisci acid)
• the formation of roots and root hairs
• induces flowering in the pineapple family and
  mango
• (inhibits flowering in many species, changes
  the sex of developing flowers)
• enhances the rate of leaf and flower senescence
• defense response (jasmonic acid)
• abscission zone formation

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Promotes the ripening of some fruits

• Ripening
• the enzymatic breakdown of the cell wall
  starch hydrolysis sugar accumulation organic
  acids and phenolic compounds (tannins) disappear
  chlorophyll loss and anthocyanins and carotenoids
  accumulation aroma and flavor components
  produced drying for some fruits.
• Climacteric (N. or adj)
• the fruits that ripen in response to
  ethylene exhibit a characteristic respiratory
• rise before the ripening phase
• Autoctalytic
• treatment with ethylene induces the
• fruit to produce additional ethylene
• Nonclimacteric (adj) fruits
• do not exhibit the respiration
• and ethylene production

banana
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(No Transcript)
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Leaf and flower senescence
Silver thiosulfate a potent inhibitor of
ethylene action
Copper cofactor requirement for high-affinity
ethylene bind to its receptor
Ethylene accelerate Cytokinin delay ABA Ch. 23
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Flooding (waterlogging) or anaerobic condition
around the root ? Ethylene production in shoot,
epinastic response
ACC is transportable Ethylene can not be
transported
( in the xylem)
(in the petiole)