Chapter 22 Ethylene: the gas hormone

1. 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.

2. 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.

3.    CO2 (p. 572) Absorbent: alkaline KMnO4 Exogenous ACC, ethephon (p. 584) Major: Minor: GACC, 1-(-L-glutamylamino) cyclopropane-1-carboxylic acid

4. 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.

5. 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

6. 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

7. 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

8. 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

10. 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

11. 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)