Ethylene

ethylene biosynthesis and its role in fruit ripening

1. ETHYLENE – ITS ROLE, BIOSYNTHESIS AND EFFECTS   PRESENTED BY V.DHANALAKSHMI

2. Introduction Ethylene is a natural plant hormone released by all plant tissues and microorganisms . It is also called ‘Ripening hormone’, as it plays an important role in ripening process. Low concentration of 0.1-1.0 microlitres is sufficient to trigger the ripening process in climacteric fruits.

3. It has autocatalytic activity because of which such small quantities can trigger further release of large quantities of ethylene by the fruit tissue. Very little response is only seen to exogenous application of ethylene in case of non-climacteric fruits.

4. Effect ethylene on fruit ripening Ethylene decides the post harvest life of fruits, vegetables and cut flowers. Synthesis of ethylene varies with maturity of fruits, vegetables and flowers. Synthesis of ethylene is less in young buds while it is more in opened and senescing fruits, vegetables and flowers. Endogenous ethylene production takes place in the style which triggers wilting and senescence of flowers. The most accepted pathway for synthesis of ethylene is methionine pathway.

5. Biosynthesis of ethylene Inhibitors Enzymes Methionine Adomet synthase     SAM (S Adenosyl Methionine ) AOA , AVG ACC synthase       ACC (1 - Amino Cyclo propane 1 - Carboxylic acid) Cobalt, Temp > 35 o C, CO 2   ACC oxidase       Ethylene

6. AOA - Aminooxyacetic acid AVG - Amino ethoxy vinayl glycine ACS - ACC Synthase ACO - ACC oxidase (Ethylene forming enzyme, EFE)

7. Factors governing the activity of ACC synthase Stage of senescence Production of ethylene is less in young flowers. Production of ethylene increases during flower maturation, opening and senescence of flowers. Auxin level During pollination, auxin is transferred from pollen to stigma. Auxin induces the production of ethylene. This auxin induced ethylene increases the synthesis of ethylene Physical injury Physical injury induces the synthesis of ethylene Chilling injury Chilling injury induces the synthesis of ethylene

8. Action of ethylene C 2 H 4 + Receptor (Copper) C 2 H 4 - Receptor complex Accelerate senescence Ag ++ replaces the copper which delays the senescence

9. Classification of horticultural commodities based on ethylene production rate Class Range at 20 o C (μ C 2 H 4 kg / hr) Commodities Very low < 0.1 Artichoke, Asparagus, Cauliflower, Cherry, Citrus fruits, Grape, Cut Flowers, Leafy Vegetables, Pomegranate, Potato, Root Vegetables, Strawberry Low 0.1-1.0 Brinjal, Chilli, Cucumber, Green Capsicum, Okra, Pine apple, Pumpkin, Water melon Moderate 1.0 -10 Banana, Guava, Fig, Litchi, Melon, Mango, Tomato High 10-100 Apple, Apricot, Avocado, Kiwi Fruit (ripe), Papaya, Peach, Plum, Pear Very high > 100 Sapota, Passion Fruit

10. Sources of ethylene Ethylene gas – Pure C 2 H 4 gas enclosed in the can/cylinder is sprayed /injected into chamber. Ethylene portable can which contain 3 g sufficient to ripe 2-6 ton of produce is available commercially Ethephon – Used as spray/ dip, acidic in water releases C 2 H 4 Ethylene mixture - C 2 H 4 + inert gas like CO 2 . Inert gas because not enough O 2 remains in the chambers to provide an explosive mixture. Eg , Ripegas contain 6% C 2 H 4 Ethylene generators - Widely used method where in liquid spirit produces C 2 H 4 when heated in the presence of catalyst platinised asbestos. Use of ripe fruits – Cheap and simple, where in ripe fruit with high C 2 H 4 producers such as apple, banana, mango, sapota and tomato is used at home to ripe / degreen

11. Removal of ethylene Eliminate the ethylene sources Provide proper ventilation KMnO 4 oxidizes the ethylene KMnO 4   C 2 H 4 CO 2 + H 2 O   Brominated or activated charcoal absorbs ethylene  

12. Ethylene inhibitors Silver chloride (AgCl 2 ) Silver nitrate (AgNO 3 ) Silver Thio Sulphate (STS) Methyl Cyclo Propane (1- MCP)

13. Regulation of ethylene in storage Hypobaric storage In hypobaric storage, action of ethylene is low due to the easy movement of silver ions at low pressure. Controlled atmosphere storage The rate of ethylene synthesis is low at high CO 2 and low O 2 .  

14. Thank you