Auxins regulate plant growth and development. They affect the growth of stem tips, leaves, roots, side branches, and fruit. Auxins are able to do this through stimulating cell elongation or inhibiting cell growth. Auxins are essential in affecting plant tropisms, or the plants reactions to stimuli, affecting which way they are facing. For example, auxins stimulate the cell growth of a plant leaning towards darkness and cause it to face the light. Scientists have been able to create chemical compounds that manipulate auxins so that certain plants grow differently.
http://kidsresearchexpress.blogspot.com/2008/09/auxin.html
http://images.tutorvista.com/content/plant-growth-movements/coleopite-auxin-distribution-hypothesis.jpeg
Abscisic acid
Abscisic acid is a hormone that affects dormancy and inhibits cell growth when a plant is under stress. For example, when a plant is lacking water, abscisic acid suspends cell growth and division and causes the plant to become dormant. Also, it causes spots on leaves that ingest water to close up and gives buds and fruit a hard outer covering to survive harsh conditions.
http://www.wisegeek.com/what-is-abscisic-acid.htm
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Ethylene
Ethylene is a gaseous hormone that stimulates ripening and the release of dormancy after the stress explained above is over. It stimulates leaf and fruit abscission, meaning it sheds the outer covering created by abscisic acid. Ethylene counteracts everything abscisic acid does after the plant is safe again. Lastly, it stimulates flower opening.
http://www.plant-hormones.info/ethylene.htm
http://www.hort.cornell.edu/mattson/leatherwood/files/Fig3.jpg
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