Chapter 22 Ethylene: the gas hormone ¤ Discover: coal gas was used for street illumination the serious defoliation of trees closing street-lamp lighter.

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.

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: 1L L-1.

CO2

(p. 572)

Absorbent:

alkaline KMnO4

GACC, 1-(-L-glutamylamino) cyclopropane-1-carboxylic acid

Exogenous ACC, ethephon

(p. 584)

Major:

Minor:

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.

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 auxins–induced ethylene production.

¤ circadian: peaking during the day and reaching a minimum at night

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 (5~10%) –antagonist, less efficient than silver ions.

trans-cyclooctene

1-methylcyclopropene (MCP)

remove ethylene

alkaline potassium permanganate

lysophospatidylethanolamine

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

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

Leaf and flower senescence

Ethylene: accelerate

Cytokinin: delay

ABA: Ch. 23

Silver thiosulfate: a potent inhibitor of ethylene action

Copper cofactor requirement for high-affinity ethylene bind to its receptor

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)