Biology of ethylene. What is ethylene? C 2 Very simple molecule A gas An important chemical feedstock A natural plant hormone.

Transcription

1 Biology of ethylene production & action What is ethylene? C 2 H 4 Very simple molecule A gas An important chemical feedstock A natural plant hormone Page 1

2 Where does ethylene come from? Ripening fruits Smoke Vehicle exhausts Ripening rooms Ripening fruit Ethylene - an important factor Useful: Accelerates ripening Causes abscission A problem: Accelerates ripening Accelerates senescence Causes abscission Page 2

3 History of ethylene biology Prehistoric Fruit ripening, smoky rooms, ripening fruit Amos, 1000 B.C. Scarification of figs - wound ethylene Neljubow, 1907 Ethylene gas - plant growth regulator Cousins, 1913 Ethylene causes ripening Gane, 1932 Produced by ripening fruits Goeschl and Pratt, 1960 Role in plant growth and development Plant hormone Veen, 1978 Silver thiosulfate Yang, 1979 Ethylene biosynthesis pathway Bleeker, 1988 Etr-1 Sisler and Blankenship, MCP Page 3

4 Ethylene responses Reduction in growth (seedlings) Loss of leaves and flowers (plants) Leaf yellowing or death (plants) Epinasty (leaves) Senescence (flowers) Ripening (fruits) Abscission (fruits, leaves, branches) Dehiscence (seeds) Seedling growth Ethylene Neljubow, a graduate student in Russia, was the first to show that ethylene caused these strange effects on etiolated pea seedlings Air Page 4

5 Carnation model system Page 5

6 Characteristics of ethylene responses Threshold concentration (0.1 ppm) Plateau concentration (10 ppm) Associated respiration rise Temperature optimum (15-25 C) CO2 (>1%) inhibits Abscission of snapdragon flowers in response to ethylene shows a typical threshold and plateau response Page 6

7 Respiration - important physiological indicator Non-climacteric Climacteric fruits 140 fruits Respiration and 120 Respiration ethylene production falls 100 steadily rises during throughout ripening 80 development Ripening induced by 60 Ethylene ethylenenot involved 40 in Bananas, ripening i apples, 20 Citrus, avocados, grapes, tomatoes, olives, 0 cherries, pears, many berries tropicals ration (mg CO2/kg/hr) Respir 1 4 Tomato 7 Strawberry Strawberry Time (days) Respiration and ethylene production rise during fruit ripening Page 7

8 Ethylene as a ripening trigger Once ripening is initiated, climacteric fruits produce ethylene Ripening is then self-controlled Tools for working with ethylene: Measurement Expensive, but routine Bioassay - cheap, difficult Kitagawa tubes - $2 / measurement Proprietary analyzers - $500 - $1000 Gas chromatograph - $10,000 - $30,000 Photo-acoustic detector - $50,000 Page 8

9 Detector Oven Electrometer Tools for working with ethylene: Application Ripening i fruits Ethylene gas Acetylene, CO Ethephon Liquid, spray, drench Gas, closed space Page 9

10 Unsprayed Gravenstein Sprayed Uses of ethylene in horticulture Induction of flowering Bulbs, Pineapple & other Bromeliads Harvest aid Walnuts, Sour cherries Induction of ripening or coloring Bananas, Citrus Page 10

11 Ethylene biosynthesis NH 3 + CH 3 -S-CH 2 -CH 2 -CH-COO - Methionine ACC synthase H 2 C CH 2 C - + OOC NH3 MET SAM synthase + NH 3 + CH 3 -S-CH 2 -CH 2 -CH-COO - Adn SAM S-adenosyl methionine ACC 1-aminocyclopropane-1-carboxylic acid ACC oxidase CH 2 =CH 2 Ethylene Page 11

12 The Yang Cycle MET Ethylene SAM synthase S-methyl thioribose ACC oxidase - Low O 2 SAM AVG/AOA S-methyl thioadenosine ACC N-malonyl transferase ACC synthase MACC malonyl ACC Molecular manipulation of ripening Anti-sense ACC synthase Anti-sense ACC oxidase Result - fruits that ripen very slowly, require ethylene treatment to ripen Just like Never Ripe (NR), a tomato mutant, used to develop long shelf-life tomatoes Page 12

13 Anti-sense ACC oxidase in melons Page 13

14 Anti-sense technology will improve marketing of many fruits Deleterious effects of ethylene Plants Growth distortion Leaves Yellowing, abscission, necrosis Flowers Senescence, abscission Fruits Ripening, softening Page 14

15 Overcoming ethylene effects Avoidance Removal Inhibition of production Inhibition of action Germplasm selection/engineering Page 15

16 Avoidance Keep ethylene sources away from sensitive products Electric fork-hoists, floor polishers Page 16

17 Removal Ventilation 1 air exchange per hour with fresh air Chemical oxidation KMnO 4 Oxidation O with UV lamps Page 17

18 Inhibition of ethylene action Controlled and modified atmospheres Low oxygen, high CO 2 inhibit production, action Silver thiosulfate Registered for cut flowers Cyclopropenes 1-MCP Registered for many crops Page 18

19 Page 19 Inhibition of ethylene responses - STS

20 1-MCP - a gaseous ethylene inhibitor Ed Sisler, NCSU Mimics ethylene, blocks the binding site Marketed for fruits and vegetables as SmartFresh Ethylene 1-MCP EthylBloc sachets in shipping boxes Photos: George Staby Page 20

21 Already in use to extend life of fruits and vegetables 1-MCP Control Avoiding ethylene effects Selection of ethylene-resistant y germplasm Page 21

22 Vanilla Bronze Avoiding ethylene effects Understanding ethylene action Biotechnology to interfere with the action cascade Page 22

23 etr1 mutation Mechanism of ethylene action Page 23

24 Biotechnology! Use of the ethylene receptor gene Insert mutated gene in sensitive plant - becomes insensitive Use tissue-specific, or stage-specific promoter - ethylene action is inhibited only in that tissue or at that time (e.g. mature flowers, ripe fruits) Already done with petunias, carnations Page 24

25 New technology use inducible promoters Application of a simple chemical or physical stress Alcohol, dexamethasone, copper, heat Drives synthesis of a gene For example, DEX/etr1 Inducible inhibition of ethylene Page 25

26 Questions? Page 26