AUXINS AND PHOTOTROPISM
Auxins are a group of plant hormones that play a crucial role in plant growth and development. They are primarily involved in cell elongation, regulating the formation of roots and shoots, and mediating tropic responses such as phototropism.
Phototropism is a plant's directional growth response to light. It is the process by which plants bend or curve towards a light source. This response occurs due to the redistribution of auxins in the plant tissue.
When light is perceived by the plant, it triggers an increase in auxin concentration on the shaded side of the stem or shoot. This higher concentration of auxin promotes cell elongation, causing the stem to bend towards the light source.
The mechanism behind phototropism involves the movement of auxins from the shoot apex downwards. In response to light, auxins accumulate on the shaded side of the plant, inhibiting cell elongation in that region. Meanwhile, the illuminated side of the plant has lower auxin concentration and experiences normal cell elongation. This difference in auxin distribution leads to bending towards the light.
Overall, auxins regulate phototropism by promoting cell elongation on one side of the plant and inhibiting it on the other, resulting in the bending movement towards the light source.
Auxins are a group of plant hormones that play a crucial role in growth and development. They regulate numerous processes in plants, including cell elongation, branching, root development, and phototropism.
Phototropism is a plant's response to light, where the plant grows towards or away from a light source. In phototropism, auxins play a vital role. Here are the steps involved in phototropism:
1. Perception of light: Plants have light-sensitive cells called photoreceptors, such as phytochromes, cryptochromes, and phototropins. When a plant is exposed to light, these photoreceptors perceive the light signals.
2. Redistribution of auxins: When light is perceived by the photoreceptors, it triggers the unequal distribution of auxins within the plant. Normally, auxins are produced in the apical meristem (the growing tip of a plant). However, during phototropism, the concentration of auxins increases on the shaded side of the plant, while it decreases on the side exposed to light.
3. Cell elongation: Auxins promote cell elongation by loosening the cell wall, allowing the cells to expand. In the case of phototropism, higher concentration of auxins on the shaded side compared to the light-exposed side leads to increased cell elongation on the shaded side, causing the plant to bend towards the light.
4. Differential growth: As the cells on the shaded side elongate more than those on the light-exposed side, this asymmetrical cell growth causes the plant to bend towards the light source.
5. Hormonal regulation: Other hormones, such as cytokinins, gibberellins, and ethylene, also interact with auxins to regulate phototropism. They help in coordinating various growth processes in response to light signals.
Overall, auxins mediate phototropism by redistributing and regulating the growth of plant cells, causing the plant to bend towards the light source.