Question

What prevents the fruit and leaf to drop in early? (a) \(\mathrm{ABA}\) (b) IAA (c) NAA (d) Both (b) and (c)

Short answer

The hormones that prevent early fruit and leaf drop are Both (b) and (c), i.e., IAA and NAA.

Step-by-step solution

Understanding ABA

Abscisic Acid (ABA) is often called the 'stress hormone' of the plant. It's generally involved in responding to environmental stresses, such as drought or cold temperatures. While ABA does play a role in leaf and fruit abscission—the process by which plants shed particular parts—it does not typically prevent early drop.

Understanding IAA

Indole Acetic Acid (IAA) is one of the most important plant hormones. As an auxin, it plays a vital role in almost every aspect of plant growth and development. One of its key roles is promoting cell elongation, which helps fruits and leaves stay attached to the plant. So, IAA helps prevent premature leaf and fruit drop.

Understanding NAA

Naphthaleneacetic Acid (NAA) is a synthetic auxin and used as a plant growth regulator. Like IAA, it can also be used to delay fruit drop.

Choosing the Correct Answer

From the above information, it can be concluded that both IAA and NAA prevent early fruit and leaf drop. Therefore, option (d) Both (b) and (c) - i.e., both IAA and NAA - is the correct answer.

Key concepts

Abscisic Acid (ABA)

Abscisic Acid, commonly abbreviated as ABA, is a plant hormone with a crucial role in plants' responses to stress.

ABA is often dubbed the 'plant stress hormone' due to its involvement in managing the challenges posed by environmental factors such as drought, salinity, and extreme temperatures. It prompts the plant to conserve water by triggering the closure of stomata, the tiny pores on leaves that facilitate gas exchange. ABA also influences seed dormancy, ensuring that seeds only germinate under favorable conditions.

However, contrary to what its name might suggest, ABA does not typically prevent the early dropping of fruit and leaves, a process known as abscission. Its presence is indeed associated with abscission zones, but it more often signals for cells to detach rather than retain them.

Indole Acetic Acid (IAA)

Indole Acetic Acid, or IAA, is an endogenous auxin which plays a pivotal role in plant growth and organ development.

IAA is fundamental in regulating various plant growth processes, including cell elongation, bud formation, and root growth. One of the key features of IAA that's particularly crucial is its ability to prevent the premature dropping of fruits and leaves. This auxin promotes the growth and elongation of cells within the plant, which helps to keep these organs attached to the main body of the plant for as long as necessary.

The application of IAA in agriculture is an essential aspect of ensuring crop productivity by mitigating early fruit drop, thereby improving the yield of fruit-bearing plants.

Naphthaleneacetic Acid (NAA)

Naphthaleneacetic Acid, also known as NAA, is a synthetic auxin that functions similarly to IAA.

This plant growth regulator is widely used in agriculture to control and coordinate various aspects of plant development. Its synthetic form allows for more controlled application compared to naturally occurring auxins. NAA is particularly known for its role in suppressing the abscission process. By mimicking the action of natural auxins like IAA, NAA helps to keep fruit and leaves from dropping prematurely. Its use in horticulture is crucial for the retention of fruits until they reach optimal ripeness, enhancing both the quality and quantity of harvests.

Auxins in Plants

Auxins are a class of plant hormones that have a significant impact on the direction and nature of plant growth.

Auxins, such as IAA and NAA, have the fascinating ability to regulate various plant processes like cell division, differentiation, and elongation. They are particularly famous for their role in phototropism, the process by which plants grow towards light, and gravitropism, which refers to growth in response to gravity. In the context of fruit and leaf retention, auxins work by strengthening the cells in the stem, ensuring that the fruit and leaves remain firmly attached to the plant body until they are fully mature or until the plant initiates a controlled abscission process. Auxins are not just limited to growth; they also play a role in plant reproductive processes and can be applied to propagate plants from cuttings.

Plant Growth Regulators

Plant Growth Regulators (PGRs) are chemicals that, in small amounts, greatly affect the growth and differentiation of plant cells, tissues, and organs.

PGRs encompass a diverse group of organic compounds, including hormones such as auxins, cytokinins, gibberellins, and ethylene. These regulators can be natural or synthetic and are used to manipulate plant growth in a controlled manner. They are extensively applied in agriculture and horticulture to manage plant development processes such as flowering, fruit set, ripening, as well as to prevent premature fruit and leaf drop. Farmers and gardeners use PGRs to optimize plant growth, increase crop yields, and improve product quality.

Abscission in Plants

Abscission is the process by which plants shed leaves, fruit, flowers, or other parts in a highly controlled and natural manner.

This process is critical for plant health and survival, allowing for the removal of parts that are no longer beneficial, such as ripe fruit or senescent leaves. Abscission involves the formation of an abscission zone, typically at the base of the stem structure, where cells begin to break down and facilitate the separation of the plant part from the main organism. While PGRs like IAA and NAA can inhibit abscission, thereby preventing premature dropping, other factors such as ethylene and environmental conditions can promote it. Abscission allows plants to conserve resources, protect against disease spread, and prepare for changing seasons.