Ethylene biosynthesis and role in plants

HISTORY OF ETHYLENE

• During the 19th 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.

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 plasmamembraneinto the cell, easily diffuse within the plant, and flushed out of plant tissues through intercellular spaces

STRUCTURE AND BIOSYNTHESIS

• Ethylene is the simplest olefin (mol. Wt. 28) .

• It is lighter than water under physiological conditions and readily undergoes oxidation.

BIOSYNTHESIS

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.

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.

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

PHYSIOLOGICAL EFFECTS OF ETHYLENE

• Fruit ripening.

• Plumular hook formation.

• Triple response.

• Formation of adventitious roots and root hairs.

• Leaf epinasty.

• Senescence.

• Abscission of leaves.

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.

MECHANISM

References

• Taiz L.&Zeiger E.2010Plant Physiology 5th Ed. Sinauer Associates,inc.

• JainVK.1974.fundamentals of Plant physiology 1st

Ed.S.Chand.publishing

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