Question

Removal of auxin source demonstrates that leaf abscission is _________ by auxin, and apical dominance is _________ auxin. a) promoted, promoted b) inhibited, inhibited (c) promoted, inhibited (d) inhibited, promoted

Short answer

Leaf abscission is inhibited by auxin, and apical dominance is promoted by auxin. The correct answer is (d) inhibited, promoted.

Step-by-step solution

Understanding the role of Auxin in Leaf Abscission

Leaf abscission is the process where a plant sheds one of its parts, like a leaf or a fruit. When the source of auxin is removed, the process of abscission is accelerated because auxin helps to suppress this process. Therefore, leaf abscission is inhibited by auxin.

Understanding the role of Auxin in Apical Dominance

Apical dominance is the phenomenon where the main, central stem of the plant grows more strongly than the side stems. Auxin, which is produced at the tip of the plant, promotes apical dominance by inhibiting the growth of lateral buds. Thus, apical dominance is promoted by auxin.

Combining both concepts to fill the blanks

Given the roles auxin plays in both processes, leaf abscission is *inhibited* by auxin, and apical dominance is *promoted* by auxin. Therefore, the correct answer is (d) inhibited, promoted.

Key concepts

Leaf Abscission

Leaf abscission refers to the natural process whereby plants shed older leaves, fruits, or seeds. This process is pivotal for the health and reproduction of a plant. Auxin, a crucial plant hormone, plays a significant role in regulating leaf abscission by delaying the onset of this shedding process. In the absence of auxin, cells at the abscission layer at the base of the leaf stem receive a signal to begin the breakdown of cell walls. As these cells weaken, the leaf or fruit is eventually dropped.

The concept of leaf abscission is linked to the plant's lifecycle and resource management. As seasons change, some plants drop their leaves to preserve resources and survive adverse weather such as winter or drought. The regulation by auxin ensures that the timing of this occurrence is optimal for the plant's overall well-being.

Apical Dominance

Apical dominance is a growth pattern in plants where the main stem grows vertically, suppressing the growth of lateral (side) buds that would otherwise produce branches. This phenomenon is primarily regulated by auxin produced in the apical meristem, or growing tip, of the plant. Auxin is transported downward from the tip and inhibits the growth of lateral buds, ensuring the plant grows tall and straight, which is especially beneficial when light is a limiting factor.

Plants demonstrate remarkable adaptability through apical dominance, investing their energy in growing towards the light and efficiently using their resources. For gardeners and farmers, understanding apical dominance is useful as pruning strategies often involve manipulating levels of auxin to encourage desired growth patterns in plants.

Plant Hormones

The Role of Auxin

Auxin is one of the primary plant hormones and is fundamental to plant growth and development. It not only inhibits leaf abscission and promotes apical dominance but also plays a crucial role in processes such as cell elongation, root growth, and fruit development. Beyond auxin, other hormones such as cytokinins, gibberellins, ethylene, and abscisic acid each have specific roles in the life of a plant, and together they form a complex regulatory network.

Plant hormones like auxin are key players in the adaptability and survival of plants. They act as chemical messengers, triggering and regulating physiological processes, which enable plants to respond dynamically to their environment.

Lateral Bud Growth Inhibition

Lateral bud growth inhibition is an outcome of apical dominance where the development of new branches from the lateral buds is suppressed. This effect is largely due to the concentration of auxin, which diffuses from the apical meristem towards the lower parts of the plant. High concentrations of auxin directly impede the growth of these buds, thus favoring the vertical growth of the plant and maintaining a single dominant main stem.

Understanding this mechanism is essential for horticulturists and agriculturists who may manipulate auxin levels through pruning or by applying hormone-based solutions to encourage branching in plants for aesthetic or crop yield reasons.