Role of Auxin in Tropism | Biology for JAMB PDF Download

Introduction

Auxin is a plant hormone that plays a crucial role in various physiological processes, including plant growth and development. One of the significant effects of auxin is its influence on tropism, which refers to the growth or movement of a plant in response to external stimuli. In this note, we will explore the role of auxin in different types of tropism and its mechanism of action.

Phototropism

• Phototropism is the growth or movement of plants in response to light.
• The primary regulator of phototropism is auxin, primarily the hormone auxin indole-3-acetic acid (IAA).
• When light is detected by photoreceptors in the plant's shoot tip, IAA moves from the shaded side to the illuminated side.
• Higher concentration of IAA on the shaded side stimulates cell elongation, causing the plant to bend toward the light source.

Geotropism

• Geotropism is the growth or movement of plants in response to gravity.
• Auxin also plays a crucial role in geotropism, specifically in both positive (roots growing downward) and negative (stems growing upward) gravitropism.
• In roots, auxin accumulates in the lower side, inhibiting cell elongation and causing the root to grow downward.
• In shoots, auxin accumulates in the upper side, promoting cell elongation and causing the stem to grow upward.

Thigmotropism

• Thigmotropism is the growth or movement of plants in response to touch or mechanical stimuli.
• Auxin is involved in thigmotropic responses, allowing plants to respond to physical contact.
• When a plant comes in contact with an object, auxin accumulates on the side away from the touch, resulting in increased cell elongation and bending toward the object.

Hydrotropism

• Hydrotropism is the growth or movement of plants in response to water.
• Auxin also plays a role in hydrotropic responses by regulating the direction of root growth towards water.
• The concentration of auxin is higher on the side of the root facing away from the water, causing increased cell elongation and bending towards the water source.

Conclusion

Auxin, as a plant hormone, plays a fundamental role in various tropic responses exhibited by plants. In phototropism, auxin regulates the bending of plants towards light. In geotropism, it controls the downward growth of roots and upward growth of stems. Thigmotropism allows plants to respond to touch, and hydrotropism directs root growth towards water sources. Understanding the role of auxin in tropism is essential in comprehending plant growth and adaptation to the environment.