What is the name of the substance that influences trophic growth movement of roots and shoots?
1 Answer
Auxin (Indole-3-acetic acid, commonly called IAA) influences geo-tropic movements of root and shoot and phototropic movements of shoot.
Explanation:
The phototrophic movements of shoot occur due to the unequal distribution of auxin on the side of the shoot facing light and the side away from light.
Auxin is synthesized in shoot apex and moves downwards.
When the shoot is exposed to unidirectional light, the auxin concentration in the shoot becomes different on the side towards the light and away from light.
Auxin gets oxidized on the side exposed to light and partially moves to the other side to prevent its oxidation. As a result of this the concentration of auxin becomes higher on the side away from the light as compared to that on the side exposed to light.
Auxin causes cell elongation. The cells of shoot away from the light elongate more and thus the shoot bends towards the light.
Similarly, the geotropic responses of shoot and root are also due to unequal distribution of auxin caused by gravitational pull. A plant is placed horizontally, the concentration of auxin becomes higher on the lower side as compared to that on the upper side.
Higher concentration of auxins promote growth in the region of shoot and retard growth in the region of root. Thus shoot bends away from gravity and root bends towards the gravity.
