Problem 160 - Objective Biology for NEET

Question

Which of the following PGR is used to break seed and bud dormancy? (a) Auxins (b) Gibberellins (c) Cytokinins (d) Ethylene

Step-by-Step Solution

Answer

The PGR that breaks seed and bud dormancy is Gibberellins

Step 1: Understanding Plant Growth Regulators (PGRs)

Plant Growth Regulators (PGRs) are naturally occurring or synthetically produced compounds that can profoundly influence plant growth and development. PGRs play crucial roles in plant growth including seed germination, dormancy, maturation, and flower growth. Different PGRs have different function roles in plant growth.

Step 2: Identifying the Function of Each Given PGR

Auxins usually promote cell elongation and are involved in various plant growth phenomena. Gibberellins are known for breaking dormancy and promoting budding. Cytokinins promote cell division, and Ethylene controls the ripening of fruits.

Step 3: Matching the Correct PGR with the Given Condition

From the given options in the problem, and based on the understanding of the roles of each PGR, Gibberellins appears as the correct choice since they are known for breaking dormancy and promoting budding.

Key Concepts

Seed and Bud Dormancy

Understanding the mechanisms behind seed and bud dormancy is key for students and professionals involved in agriculture and horticulture. Dormancy is a survival strategy that ensures seeds and buds do not germinate or grow until conditions for survival, such as the right temperature and moisture levels, are optimal.

During this period, growth inhibitors may dominate, and breaking this dormancy typically involves the removal or reduction of these inhibitors or an increase in growth promoters. One way to break dormancy is by using certain Plant Growth Regulators (PGRs), specifically gibberellins, which can be applied to seeds or buds to stimulate them to resume growth.

Auxins

Auxins are a class of PGRs that are fundamental to plant growth and development. These hormones regulate a wide range of processes, from cell division and elongation to the differentiation of tissues. Auxins commonly facilitate the formation of roots and are therefore used for root induction in cuttings.

This group of PGRs also plays a pivotal role in the tropic responses of plants, which includes how plants grow towards light or against the force of gravity. Agricultural practices often harness the power of synthetically produced auxins to promote uniform fruit development and prevent premature fruit drop.

Gibberellins

• Growth and development: Gibberellins are involved in promoting growth and development throughout the plant's life cycle.
• Seed germination: They help in breaking seed dormancy, a process critical for seeds to begin germinating.
• Stem elongation: Gibberellins contribute significantly to internodal spacing, making plants and fruits grow longer.
• Flowering: These hormones can induce flowering in certain plants and can influence the sex expression.
• Fruit growth: Gibberellins can also enhance fruit size and quality.

Gibberellins' role in resolving dormancy relates to their ability to counteract the effects of inhibitors and to modify gene expression in favor of germination or bud growth.

Cytokinins

Cytokinins are a set of PGRs that predominantly regulate cell division, or cytokinesis, in plants. They are also influential in delaying senescence, the process of aging in plants. By promoting nutrient mobilization, cytokinins keep the vegetative tissue young and active.

They have an antagonistic relationship with auxins that helps to maintain a balance between root development and shoot growth. Cytokinins are used in tissue cultures to induce shoot proliferation and to help establish a sustainable balance of root and shoot systems when cloning plants.

Ethylene

Ethylene, a gas hormone, has a simple molecular structure but a profound impact on plant life cycles. Its functions stretch from seedling growth to fruit ripening and flower wilting. As a stress hormone, it can be induced by mechanical wounding, waterlogging, and infection.

It's widely known for its role in the ripening of fruits, where it increases the rate at which fruits soften, changes their color, and enhances the release of other volatiles that contribute to flavor. In commercial fruit production, ethylene is either applied or inhibited to manage ripening during storage and transport.