Biology of ethylene production & action in fruits What is ethylene? C 2 H 4 Very simple molecule A gas An important chemical feedstock A natural plant hormone Page 1
Where does ethylene come from? Smoke Vehicle exhausts Ripening rooms Ripening fruits Ethylene - an important factor Useful: Accelerates ripening Causes abscission A problem: Accelerates ripening Accelerates senescence Causes abscission Page 2
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 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, 1996 1-MCP 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) Page 4
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 Carnation model system Page 5
Characteristics of ethylene responses Threshold concentration (0.1 ppm) Plateau concentration (10 ppm) Associated respiration rise Temperature optimum (15-25 C) CO2 (>1%) inhibits Page 6
Abscission of snapdragon flowers in response to ethylene shows a typical threshold and plateau response The ethylene response cascade Page 7
Respiration - important physiological indicator Non-climacteric Climacteric fruits fruits Respiration and Respiration ethylene production falls steadily rises during throughout ripening development Ripening induced by Ethylene ethylenenot involved in Bananas, ripening apples, Citrus, avocados, grapes, tomatoes, olives, cherries, pears, many berries tropicals Respiration (mg CO2/kg/hr) 140 120 100 80 60 40 20 0 1 4 7 Strawberry Tomato Strawberry 10 13 16 Time (days) 19 22 25 28 Respiration and ethylene production rise during fruit ripening Page 8
Ethylene is a ripening trigger in climacteric fruits Once ripening is initiated, climacteric fruits produce ethylene Ripening is then self-controlled 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 Page 9
Tools for working with ethylene: Measurement Expensive, but routine Bioassay - cheap, difficult Kitagawa tubes - $2 / measurement Proprietary analysers - $500 - $10,000 Gas chromatograph - $10,000 - $30,000 Photo-acoustic detector - $50,000 Detector Oven Electrometer Page 10
Sensorsense Photoacoustic Ethylene Detector Page 11
A nanotechnology ethylene detector Based on the ethylene binding site Carbon nanotubes doped with copper When ethylene binds, the electrical properties of the nanotubes change Tools for working with ethylene: Application Ripening fruits Ethylene gas Gas, closed space Acetylene, CO Ethephon Liquid, spray, drench Page 12
Unsprayed Gravenstein Sprayed hephon-treated Control Page 13
CaC2CaO 2 + H 2 + O 2C = C= 2 Ca H 22 (+ C + C 2 CO H 4 ) 2 + CaO Molecular manipulation of ripening 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 14
Reid, Michael "Biology of Ethylene Production and Action in Fruits" 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 Anti-sense ACC oxidase in melons Page 15
Anti-sense technology will improve marketing of many fruits Page 16
Questions? Page 17