which plant hormone is primarily involved in directional growth responses like bending of shoots towards light?
The plant hormone primarily involved in directional growth responses like bending of shoots towards light is auxin (especially indole-3-acetic acid, IAA).
Quick Scoop: Direct Answer
- The correct answer: Auxin is the main plant hormone controlling phototropism, the bending of shoots towards light.
- It works by redistributing to the shaded side of the stem, causing those cells to elongate more so the shoot curves toward the light.
How Auxin Makes Shoots Bend
Imagine a young shoot getting light from only one side.
- Light hits one side of the shoot tip.
- Auxin moves away from the illuminated side to the shaded side.
- Cells on the shaded side, now with more auxin, elongate more than cells on the light side.
- This uneven growth makes the shoot bend toward the light (positive phototropism).
So the hormone is the same everywhere, but its unequal distribution is what causes directional growth.
Related Concept: Phototropism
- Phototropism : Directional growth in response to light.
- Shoots usually show positive phototropism (toward light), which helps them capture more light for photosynthesis.
- The classic Darwin experiments on coleoptiles helped reveal that a signal from the tip (later identified as auxin) controls this bending response.
Mini FAQ
- Is any other hormone mainly responsible for this bending?
No. Other hormones like gibberellins or cytokinins affect growth, but auxin is the primary hormone for directional bending towards light in shoots.
- Is the effect the same in roots?
No. In roots, higher auxin inhibits elongation, so roots respond differently to auxin compared with shoots, especially in gravitropism, but the directional control still involves auxin gradients.
TL;DR: The plant hormone mainly responsible for directional growth like bending of shoots towards light is auxin.
Information gathered from public forums or data available on the internet and portrayed here.