Biology of ethylene production & action. Ethylene - an important factor. Where does ethylene come from? What is ethylene? Ethylene responses

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1 Biology of ethylene production & action Ethylene - an important factor CH 3 CH 3 Useful: Accelerates ripening Causes abscission A problem: Accelerates ripening Accelerates senescence Causes abscission What is ethylene? C 2 H 4 Very simple molecule A gas An important chemical feedstock A natural plant hormone Where does ethylene come from? Ripening fruits Smoke Vehicle exhausts Ripening rooms Ripening fruit History of ethylene biology Ethylene responses 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 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) 1

2 Characteristics of ethylene responses Threshold concentration (0.1 ppm) Plateau concentration (10 ppm) Associated respiration rise Temperature optimum (15-25 C) CO 2 (>1%) inhibits Abscission of snapdragon flowers in response to ethylene shows a typical threshold and plateau response Respiration - important physiological indicator Non-climacteric Climacteric fruits fruits Respiration and Respiration ethylene production falls steadily throughout rises during development ripening Ethylene Ripening not induced involved by in ripening ethylene Citrus, Bananas, grapes, apples, olives, cherries, avocados, many tomatoes, berries pears, many tropicals Respiration (mg CO2/kg/hr) Strawberry Strawberry Tomato Ethylene as a ripening trigger Once ripening is initiated, climacteric fruits produce ethylene Ripening is then self-controlled Time (days) Tools for working with ethylene: Measurement Bioassay - cheap, difficult Kitagawa tubes - $2 / measurement Proprietary analysers - $500 - $1000 Gas chromatograph - $10,000-30,000 Photo-acoustic detector - $75,000 Tools for working with ethylene: Application Ripening fruits Ethylene gas Gas, closed space Acetylene, CO Ethephon Liquid, spray, drench 2

3 Uses of Ethylene in Horticulture Induction of flowering Bulbs, Pineapple & other Bromeliads Harvest aid Walnuts, Sour cherries Induction of ripening or coloring Bananas, Citrus Unsprayed Gravenstein Sprayed 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 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 Deleterious effects of ethylene Plants Growth distortion Leaves Yellowing, abscission, necrosis Flowers Senescence, abscission Fruits Ripening, softening Detrimental Effects of Ethylene on Vegetables Commodity Beans, snap Broccoli Cabbage Carrots Cauliflower Symptoms Yellowing Yellowing, floret abscission, off-flavors Yellowing, leaf abscission Bitterness Yellowing, leaf abscission, browning of remaining leaves 3

4 Ethylene induces yellowing and floret opening of broccoli Ethylene induces leaf abscission of cauliflower Ethylene induces yellowing of cucumbers Detrimental Effects of Ethylene on Fruits Commodity Kiwifruit Avocado & Fuyu Persimmon Citrus Stone Fruits Symptoms As little as 50ppb induces softening Exposure to 1ppm at 5 C increases chilling injury symptoms Use of ethylene for degreening increases senscence Increase in decay development by accelerated softening and increased growth of fungus Ethylene accelerates softening of kiwifruits during storage at 0 C Effect of Ethylene on Watermelon Quality after 7 Days at 18ºC (64 F) C 2 H 4 (ppm) Firmness (N) Rind Thickness (mm) SSC (%) Heart Area Seed Area Acceptability (%) a 16 a b 12 b b 13 b Risse & Hatton (1982) 4

5 Detrimental Effects of Ethylene on Ornamentals Commodity Symptoms Detrimental Effects of Ethylene on Ornamentals Commodity Symptoms Cut flowers Failure-to-open of flowers cut at the bud stage, closure of open flowers Flowering bulbs Inhibition of shoot/root elongation, abnormal flowers, gummosis in tulips, flowerbud abscission (lily) Flowering plants Flower abscission, flower closure Foliage plants Leaf abscission, leaf chlorosis, epinastic responses (downward leaf curvature) Geranium seedlings Dormant nursery stock Leaf chlorosis, poor growth after planting Reduced budbreak, greater mortality after planting Ethylene induces flower abscission Ethylene-induced sleepiness of carnations Overcoming ethylene effects Avoidance Removal Inhibition of production Inhibition of action Germplasm selection/engineering Avoidance Keep ethylene sources away from sensitive products Electric fork-hoists, floor polishers 5

6 Removal Ventilation 1 air exchange per hour with fresh air Chemical oxidation KMnO 4 Oxidation with UV lamps Inhibit Ethylene Production Low 0 2 atmosphere reduces ethylene production and delays tomato ripening Inhibition of ethylene action led and modified atmospheres Low oxygen, high CO 2 inhibit production, action Silver thiosulfate Registered for cut flowers Cyclopropenes 1-MCP Registered for many crops Commercial Use of 1-MCP 1-methylcyclopropene (1-MCP) was developed by researchers at North Carolina State University Marketed by AgroFresh as: SmartFresh SM technology for fruits and vegetables EthylBloc TM technology for flowers and other ornamentals 6

7 Vegetables Benefits seen on vegetables include Reduced yellowing of leafy vegetables, herbs, beans and broccoli Reduced disorders e.g. browning and russet spotting of lettuce and spotting of beans SmartFresh SM technology SmartFresh SM technology SmartFresh SM Technology: Cucumber Sweet Marketmore slicing cucumbers after 10 days at 15 o C/59 o F SmartFresh SM Technology Better flavor e.g. reduced bitterness in carrots And probably many more undiscovered benefits SmartFresh SM technology With ethylene % damaged flowers Delphinium EthylBloc TM Sachet No sachet 0 (control) Days after ethylene exposure EthylBloc TM sachet Flowers were stored for 7 days at 36 o F + 6 days at 70 o F after exposure to ethylene. Avoiding Exposure to Ethylene - Ethylene Exclusion - Use electric fork lifts Use ethylene absorber on fork lifts Avoid other pollution sources Avoid mixing ethylene-producing and ethylene-sensitive commodities Ethylene Production by Horticultural Commodities Class µl C 2 H 4 /kg-hr at 20ºC Commodities Very low Cherry, citrus, grape, strawberry, pomegranate, leafy vegetables, root vegetables, potato, cut flowers Low Blueberry, cucumber, okra, pepper, persimmon, pineapple, raspberry Moderate Banana, fig, honeydew melon, mango, tomato High Apple, apricot, avocado, cantaloupe, feijoa, kiwifruit, nectarine, papaya, peach, pear, plum 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 Very high >100 Cherimoya, passion fruit, sapote, mammee apple 7

8 Anti-sense ACC oxidase in melons Points to Remember Learn which products are sensitive to ethylene Ethylene can be beneficial for many fruit, but stimulates ripening and senescence processes Do not mix high ethylene producing crops with ethylene sensitive crops Use of SmartFresh TM can help in mixed load situations 8