Growth in plants reflects the way in which they interact with the environment.
If we place a strong light at one side of this fuchsia plant, the plant will grow towards it. This is called the Phototrophic Response. But what controls such response?
If the typical plant is protected from a light using a small cup, the plant will continue to grow upward. This suggests that there is something at the tip of the plant that controls the direction of growth.
If we place this fuchsia plant on its side, it quickly recovers its orientation and grows upward.
But, is the plant responding to light or the gravity?
These peas seeds are germinating in the dark, yet the roots are growing down and shoots are growing up. The roots and shoots must be responding to gravity but in different ways.
The roots are said to be positively geotropic, and the shoots are negatively geotropic.
It is probable that all of these growth responses are doing some part to the Auxin/Indoleacetic Acid or IAA.
One theory states that a light sensing mechanism at the tip of the fuchsia plant promotes the active transport of IAA molecules to the shaded part of the stem.
This action produces cell growth and elongation in this area. The result is a curvature which orientates the plant towards the light.
The gravity sensing mechanism in the shoot to tip triggers the similar migration of IAA in molecules, producing growth in the stem which orientates the plant from a horizontal position back to a vertical position.
The growth substance IAA, also appears to have a roll in maintaining apical dominance. By removing the growing tip which controls auxin distribution, and therefore, apical dominance, lateral buds can grow.
An important hormone into sedulous plants is Abcisic Acid which controls leaf fall, thereby protecting the plant from adverse seasonal conditions.
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