Plant Hormones

Ethylene

http://labs.bio.unc.edu/Kieber/ethylene.htm

Ethylene comes from the endoplasmic reticulum in a plant cell. It is not very soluble, and this causes it to diffuse out of the plant cell. So the concentration of ethylene in the plant depends upon the rate at which it is produced with comparison to the rate at which it diffuses out. It functions to inhibit growth and also for ripening. It is used by farmers to force ripening of fruits, since naturally there is a burst of ethylene production just before ripening. Ethylene converts starch and acid from unripe fruits to sugar in ripe fruit.

http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=998688536&topicorder=7&maxto=11

 It is a positive feedback loop, that stimulates its own production. When the first fruit begins to ripen, it emits ethylene, which is then absorbed by the surrounding fruit, causing all of them to ripen too. Ethylene suppresses auxin (and auxin suppresses ethylene).

http://www.pnas.org/content/103/36/13286/F6.expansion.html

http://www.hort.cornell.edu/mattson/leatherwood/

The flowers disappeared because they are too sensitive to the ethylene. The ethylene also causes the plant's leaves to become more curled. Ethylene is responsible for the aging process of plants

Auxin

http://www.nature.com/nrm/journal/v7/n11/fig_tab/nrm2020_F5.html

 Auxin is produced in immature parts of plants, such as the embryo, the young leaves, and buds, and it stimulates growth. It increases the activity of the protein pump, and causes the cell wall of the plant to become more acidic and become capable of elongating. It controls cell division and can regulate fruit development, helping the fruit grow bigger. Farmers inject auxin into fruits to make them bigger.

http://www.bio.miami.edu/dana/226/226F09_13.html

http://www.tutorvista.com/content/biology/biology-iv/plant-growth-movements/growth-regulators.php

Auxin is synthesized at the tip of the plant, and gets sent to the dark side of the plant. This causes cell division on the dark side, or stem elongation, and causes the plant to bend toward the light. Auxin is part of a process known as Positive Phototropism, where a plant moves toward light.


Abscisic Acid

http://www.pnas.org/content/105/11/4495.figures-only

Abscisic acid is responsible for the dormancy of plants, inhibiting plant growth. It is produced in the terminal buds. It reduces transpiration by closing the stomata, causing low levels of water to reach the leaves. It inhibits plant growth during stress to prevent the plant from dying.