2. Background Info The ancient Egyptians were the first to use Ethylene to stimulate ripening. The ancient Chinese would also use ethylene gas produced by burning incense in closed rooms to enhance the ripening of pears. During the 1800s, when coal gas was used as fuel for streetlights, leakage from gas pipes caused nearby trees to drop leaves prematurely. The gas ethylene was demonstrated to be the active factor in coal gas around 1901. However, many people rejected the idea that ethylene was a plant hormone. It was not until the advent of gas chromatography simplified its identification.

3. Origin  This gaseous hormone can be produced in all higher plants by most parts (leaves, stems, roots, flowers, fruits, tubers, and seedlings) of the plants.  It is produced from methinonine (amino acid) in essentially all types of tissue.  It is produced in high concentrations during senescence, leaf abscission, and the ripening of some types of fruits.

4. Destination  The destination can vary depending on what function the ethylene is involved in.  During the response to mechanical stress, ethylene is sent to the stem, causing it to thicken and grow horizontally.  During senescence, ethylene is sent to the cells and/or organs of the plants that are programmed for death.  During leaf abscission, ethylene is sent to the leaves.  During fruit ripening, ethylene is produced and sent to the developing ovary to induce and quicken the ripening process.

5. Response/Function  Ethylene production has many effects on plant development; the main four are: fruit ripening, mechanical stress, senescence, and leaf abscission.  Plants produce ethylene in response to stress; the hormone instigates a growth maneuver known as the triple response.  Triple Response: The three parts of this response are a slowing of stem elongation, a thickening of the stem, and a curvature that causes the stem to start growing horizontally.

6. Response/Function  The production of ethylene also assist in senescence (the programmed death of certain cells or organs or the entire plant).  A change in the ratio of ethylene to auxin controls leaf abscission (the natural detachment of leaves of a plant).  A burst of ethylene production in the fruit triggers the ripening progress.  Positive Feedback: Ethylene triggers ripening, and ripening triggers more ethylene production.

7. Diagram http://www.nature.com/nrm/journal/v5/n2/full/nrm1317.html

8. Diagram https://digitalarchive.wm.edu/bitstream/handle/10288/2085/Honors%20 Thesis%20Complete%20Thesis.pdf?sequence=1

9. Sources http://www.nature.com/nrm/journal/v5/n2/full/nrm1317.html https://digitalarchive.wm.edu/bitstream/handle/10288/2085/ Honors%20Thesis%20Complete%20Thesis.pdf?sequence=1 http://www.plant-hormones.info/ethylene.htm Campbell NA, Reece JB. 2011, 9 th ed. San Francisco (CA): Pearson/Benjamin Cummings. 1263 p.