Ethylene biosynthesis and role in plants

Ethylene - role and biosynthesis

1. CLASS SEMINAR ON BIOSYNTHESIS OF ETHYLENE ND ITS ROLE IN PLANT GROWTH AND DEVELOPMENT BY M. ASIF WANI M Sc. Fruit Science , SKUAST-K

2. HISTORY OF ETHYLENE During the 19 th century, when coal gas was used as street illumination it was observed that trees in the vicinity of streetlamps defoliated more extensively than other trees. In 1901, Dimitry Neljubov observed that dark grown pea seedlings in the laboratory exhibited symptoms that were later termed the triple response. The first indication that ethylene is a natural product of plant tissues was published by H. H. Cousins in 1910. In 1934, R. Gane and others identified ethylene chemically as a natural product of plant metabolism, and because of its dramatic effects on plant it was classified as a hormone.

3. OCCURANCE, DISTRIBUTION AND TRANSPORT OF EHYLENE IN PLANTS Ethylene can easily be synthesized in all plant organs such as roots, stems, leaves, tubers, fruits and seeds. It is highest in senescing tissues and ripening fruits. Within the plant organs, ethylene formation is mainly located in peripheral tissues. Ethylene is biologically active at low concentration (less than 1 ppm ) Ethylene can easily pass through plasmamembrane into the cell, easily diffuse within the plant, and flushed out of plant tissues through intercellular spaces

4. STRUCTURE AND BIOSYNTHESIS Ethylene is the simplest olefin (mol. Wt. 28) . It is lighter than water under physiological conditions and readily undergoes oxidation.

5. BIOSYNTHESIS

6. CONJUGATION AND CATABOLISM OF ETHYLENE Not all the ACC found in the tissue is converted to ethylene. ACC can also be converted to a conjugated form ,N- malonyl ACC which accumulates in the tissue , primarily in the vacuole. A minor conjugated form of ACC, 1-(y-L- glutamylamino ) cyclopropane-1-carboxylic acid (GACC) has also been identified. Carbon dioxide, ethylene oxide, ethylene glycol, and the glucose conjugate of ethylene glycol have been identified as metabolic breakdown products.

7. FACTORS PROMOTING ETHYLENE BIOSYNTHESIS Fruit ripening. Stress induced ethylene production,viz Drought, flooding, chilling, exposure to ozone, and mechanical wounding. Auxin induced ethylene production. Circadian regulation of ethylene production.

8. INHIBITORS OF ETHYLENE BIOSYNTHESIS AND ETHYLENE ACTION Aminoethoxy-vinylglycine (AVG). Aminooxyacetic acid (AOA). Silver ions. Carbon dioxide at high concentrations (5-10%). trans- cyclooctene . 1-Methylcyclopropene

9. PHYSIOLOGICAL EFFECTS OF ETHYLENE Fruit ripening. Plumular hook formation. Triple response. Formation of adventitious roots and root hairs. Leaf epinasty . Senescence. Abscission of leaves .

10. MECHANISM OF ETHYLENE ACTION Binding of ethylene to a receptor. Activation of one or more signal transduction pathways. Modulation of gene expression leading to cellular response.

11. MECHANISM

12. References Taiz L.&Zeiger E.2010Plant Physiology 5 th Ed. Sinauer Associates,inc . JainVK.1974.fundamentals of Plant physiology 1 st Ed.S.Chand.publishing

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