Auxin
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Auxin
Auxin are essential plant hormones that promote the lengthening of the cell, which is a critical step before the cell goes through cell differentiation. The auxin can do this by increasing the amount of water taken in by the cell, which improves the elasticity of the cell and therefore can take more water and can get increasingly longer. And don’t think for a second that that’s all auxins do auxins may have been the first plant hormone to be discovered doesn’t make it the least important, for example the ratio of auxins to cytokinin in certain tissues can start the formation of roots instead of buds, because of this action the plant as a whole can respond to its changing environment without requiring a nervous system.
There are three different forms of native auxins including the most important of all auxins is IAA (indole-3-aceic acid) as pictured above. IAA is the most abundant and produces the most effects in plants. IAA is made in cells of the bud of plants and is synthesized from trytophan. IAA has a major impact in several plant activities such as:
Development of the embryo
Leaf formation
Apical dominance
Root initiation
Fruit development
Phototropism
Gravitropism
Abscission
Now the role auxins play in the development of an embryo, they are kind of like taxi
drivers. The gradients of the auxins guide the patterning of the embryo to the part of the where they will be stationed and become organs, organs such as the shoot apex, primary leaves, cotyledons, the stem, and the roots.
We all know that leave formation happens in the apical meristem, but what you may not know is that it is all started by the accumulation of auxin. When a leave is developing it depletes the surrounding cells so that the leaves don’t grow to close together. So auxin also provides the characteristic pattern of leaves.
The growth of the shoot apex or the terminal shoot almost always inhibits the development of lateral buds on the stem under it. This amazing happening is called apical dominance. Auxin seems to make all of this happen because it is transported downward for tha apical meristem. Here’s kind of a cool fact, if you cut off the apical meristem but apply IAA to the bottom of the stump the inhibition of the lateral buds is still maintained.
Auxin, if localized in large numbers in an epidermal cell will initiate the making of lateral or secondary roots. Auxin also stimulate the growth of adventitious