5.4.1 Control and Coordination

In this lesson, we will explore how plants coordinate and control their growth and responses to environmental stimuli through the production and distribution of hormones. Specifically, we will focusWhat the writer draws attention to at a given moment (e.g., setting, character, detail). on two important plant hormones, auxin, and their role in phototropism and gravitropism. We will also explore the roles of gibberellins and ethene in the control and coordination of plant growth and development.

Hormones in Plants

Hormones in plants are chemical messengers that regulate various physiological processes and growth responses. They are produced in specific tissues and transported to target cells or tissues, where they initiate specific biological responses.

Auxin is a plant hormone that plays a crucial role in controlling growth and development.

Phototropism

Phototropism is the growth or movement of plants in response to light. Positive phototropism refers to the growth of plant organs towards a light source, while negative phototropism is the growth away from light.

Auxin is responsible for the differential growth of plant cells, leading to phototropic responses.

• When light shines on a plant, auxin is redistributed, with higher concentrations on the shaded side.
• Increased auxin levels stimulate cell elongation on the shaded side, causing the plant to bend towards the light source.

Gravitropism (Geotropism)

Gravitropism is the growth or movement of plants in response to gravity. Positive gravitropism refers to the downward growth of roots, while negative gravitropism is the upward growth of shoots.

Similar to phototropism, auxin is involved in the differential growth of cells during gravitropic responses.

• 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 shoot to grow upward.

Gibberellins (HT only)

Gibberellins are a group of plant hormones that regulate various aspects of plant growth and development. One important role of gibberellins is their involvement in the initiation of seed germination.

Seed Germination:

• Seed germination is the process by which a dormant seed begins to grow and develop into a new plant.
• Gibberellins stimulate the synthesisCombining information from more than one text to show comparison. of enzymes that break down stored nutrients in the seed, such as starch, into sugars.
• These sugars provide the energy and resourcesThe inputs used to produce goods and services, including the factors of production. necessary for the growth of the embryonic plant.

Ethene (HT only)

Ethene, also known as ethylene, is a gaseous plant hormone involved in various physiological processes. One significant role of ethene is its control of cell division.

Cell Division:

• Cell division is the process by which a single cell divides into two or more daughter cellsThe two new cells formed after cell division..
• Ethene promotes cell division in plant tissues, leading to growth and development.
• This hormone plays a crucial role in root and shoot growth, as well as in the formation of flowers and fruits.

Fruit Ripening:

• Fruit ripening is a complex process involving changes in colour, flavour, texture, and aroma that make fruits more attractive for seed dispersal.
• Ethene is responsible for triggering and coordinating the ripening process in fruits.
  • Ethene stimulates the production of enzymes that break down complex  compounds, such as starches and acids, into simpler sugars.
  • This breakdown of compounds contributes to the sweetening of fruits and the softening of their flesh.

Conclusion

Plants possess a remarkable ability to coordinate and control their growth and responses to environmental stimuli. Hormones, particularly auxin, play a vital role in regulating these processes. Through unequal distributions of auxin, plants can achieve differential growth rates in their roots and shoots, leading to phototropic and gravitropic responses. Gibberellins and ethene play crucial roles in the control and coordination of plant growth and development. Gibberellins initiate seed germination, providing the necessary resources for seedling growth. Ethene, on the other hand, regulates cell division, promoting overall plant growth, and controls fruit ripening, making fruits more attractive for seed dispersal.