No Till Corner

Agent Orange is a 50/50 mix of the synthetic auxins

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Auxin and
Cytokinins:
Plant Hormones
Auxin Location
Auxin is mainly produced and synthesized in the apical meristems, the tips of primary growth in a plant. From here, it can be released and can adjust plant growth. Sometimes, the root apical meristems will also produce auxin.
Cytokinins Location
Cytokinins are mainly produced in the roots and then transported to certain areas as needed. Note that synthesis of cytokinins is not limited to the roots.
Target Location of Auxin
Auxin typically work in the stem and fruiting bodies and affect the cells in that area. Auxin will also work with the roots at the bottom areas of the plant.
Auxin
Effect
Cytokinins
Effect

Cytokinins Target Area
The cytokinins work in the cells of the shoots and roots and also in developing buds.
The following are the effects produced by auxin:
The following are the effects produced by cytokinins:
Cell Elongation
Lateral Root Formation
Fruit Development
Leaf Abscission Retardant
Root/Shoot Cell Division Regulation
Lateral Bud Growth Promotion
Seed Germination Stimulant
Delay of Leaf Senescence
Cell elongation is one of
the more important
functions of auxin. Only
at small concentrations
will auxin stimulate
growth (otherwise, it inhibits growth). This is caused when auxin stimulates high activity in the proton H+ pump and causes high acidity in the cell wall. Expansins, which are activiated by low pH, will loosen the wall and will allow for more uptake of water, resulting in increased turgidity. When this happens, the cell wall elongates as a result. When those cell elongate and other cells on the other side don't, the plant leans towards one side: towards the stimulus.
Once the root starts to form, auxin begins to build up and become highly concentrated in the tip, much like how it does in the top of the stem. When the root grows, auxin will stimulate growth patterns in these roots in different ways and secondary roots tend to split off in their own direction and thus we have the branching we see in roots, all caused by lateral root growth.
Once a seed is formed and finally matures, the plant will release auxin to the surrouning flower parts and fruit will form. When auxin isn't put in, fruit aren't guaranteed to grow.
Leaves and fruits generate auxin, and will stay on the plant provided that they keep producing auxin. Auxin is one reason that the leaf or fruit remains attached to the plant. Once auxin production stops and there is no trace of auxin left in the leaf or fruiting body, a cellular layer called the abscission layer forms at the base of the petiole or fruit stalk and the plant pulls the plug on the leaf or fruit.
Synergistic or Antagonistic?
Both!
It depends on the situation.
When It's Synergistic
There are times when the two are synergistic. In order for cell division to be stimulated, as stated a little earlier, auxin will allow for the cell to grow but won't cause division. Cytokinins will divide the cell that was enlarged by auxin, but adding cytokinins alone without first allowing auxin to run its course and enlarge the cell will do absolutely nothing. Both hormones are needed to properly induce a stimulated cell division. One or the other simply won't work.
When It's Antagonistic
There are also times when cytokinins and auxin will act against each other. When determining apical dominance, auxin and cytokinins will have opposite effects towards the development of axillary buds and will undo each others' actions. Auxin will suppress and hinder growth while cytokinins will counter this action and conversely promote growth of buds. This balance regulates growth of buds.
Cytokinins have the primary function above all its other functions as a regulator for cell division. To be explained more in depth later, cytokinins must work with auxin in order to stimulate cell division. (We will come back to this in a later slide and explain how cytokinins stimulate cell division in more detail.)
Until then, here's a picture of how it works...
Cytokinins determine the apical dominance for buds and support lateral bud growth. Again, this role is in a relationship to auxin in which cytokinins an auxin both work to regulate lateral bud growth. (We will also come back to this in another slide as well. These two slides will explain an important matter later on.)
Cytokinins will be found in the endosperm of many seeds that will, under certain circumstances, be triggered to initiate cell division in the embryo. Once the cytokinins begin to run their course, the embryo will rapidly grow and the seed germinates.
In some cases, cytokinin will work to delay leaf senescence, or programmed cell death. This is mainly seen as they slow the aging of leaves, which ultimately delays cell death. This works because cytokinins will inhibit protein breakdown and stimulate protein synthesis (among others like stimulated synthesis of RNA) inside cells. The more cytokinins work, the slower the leaf ages and the longer it will stay alive.
That's The End
Any questions?
What is being controlled?
You'll find that both auxin and cytokinesis both control general growth of many areas of the plant, sometimes even working the same cycles. Auxin generally controls which direction the plant grows (in response to phototropism, etcetera) while both control if the plant grows and how much the plant grows.

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