Describe gravitropism as a response in which parts of a plant grow towards or away from gravity

Sourav PanNovember 3, 2024

Answered step-by-step

Gravitropism, also known as geotropism, is a directional growth response in plants that occurs in reaction to gravity. This phenomenon enables plants to orient their growth appropriately, allowing roots to grow downward (positive gravitropism) and stems to grow upward (negative gravitropism). Here’s a detailed description of gravitropism and its significance:

Types of Gravitropism

1. Positive Gravitropism:
   • Roots: Roots exhibit positive gravitropism, meaning they grow towards the force of gravity. This growth direction helps roots anchor the plant securely in the soil and facilitates the uptake of water and nutrients from the ground. The downward growth of roots ensures that they can access moisture and minerals, which are essential for the plant’s survival.
2. Negative Gravitropism:
   • Stems and Shoots: Stems and shoots display negative gravitropism, growing away from the gravitational pull. This upward growth allows leaves to reach sunlight for photosynthesis, which is critical for energy production in plants. By growing upwards, stems can also support the plant’s structure and facilitate reproduction by allowing flowers to be positioned optimally for pollination.

Mechanism of Gravitropism

Gravitropism involves several physiological and biochemical processes:

1. Perception of Gravity:
   • Specialized cells in the plant, particularly in the root cap and stem, contain statoliths, which are dense, starch-filled organelles that settle under the influence of gravity. The movement of these statoliths within the cells helps the plant perceive its orientation relative to gravity.
2. Hormonal Response:
   • The perception of gravity triggers an asymmetric distribution of auxins, a group of plant hormones that regulate growth. In roots, auxins accumulate on the lower side, promoting cell elongation on that side and causing the root to bend downward. Conversely, in stems, auxins accumulate on the lower side as well but inhibit cell elongation there, allowing the upper side to grow faster and resulting in upward bending.
3. Cellular Growth:
   • The differential distribution of auxins leads to differential growth rates between different sides of the plant organ (roots or stems), resulting in bending towards or away from gravity.

Significance of Gravitropism

• Survival and Adaptation: Gravitropism is essential for a plant’s survival as it ensures that roots grow downwards to access water and nutrients while shoots grow upwards toward light.
• Optimal Resource Utilization: By orienting growth according to gravity, plants maximize their ability to capture sunlight for photosynthesis and absorb resources from the soil.
• Structural Stability: Proper root orientation provides stability to the plant, helping it withstand environmental stresses such as wind or heavy rainfall.