Question

Read the given statements to identify the phytohormone that performs these functions. (i) Horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. (ii) Promoting senescence and abscission lro flowers. (iii) Breaking seed and bud dormancy. (iv) Initiating germination in peanut seeds. (v) Sprouting of potato tubers. (a) \(\mathrm{ABA}\) (b) Ethylene (c) GA (d) Cytokinins

Short answer

The phytohormone that performs all the given functions is Gibberellins (GA), which is option (c).

Step-by-step solution

Identify Phytohormone for (i)

The function of causing horizontal growth, swelling, and apical hook formation in dicot seedlings is attributed to Gibberellins (GA).

Identify Phytohormone for (ii)

Ethylene is known for promoting senescence and abscission in flowers, leaves, and fruits.

Identify Phytohormone for (iii)

Gibberellins (GA) are responsible for breaking seed and bud dormancy.

Identify Phytohormone for (iv)

Gibberellins (GA) also play a role in initiating germination in peanuts seeds.

Identify Phytohormone for (v)

Sprouting of potato tubers is induced by Gibberellins (GA).

Key concepts

Gibberellins

Gibberellins are a class of phytohormones that play a pivotal role in various aspects of plant growth and development. These hormones are critical for many processes, including stem elongation, germination, and flowering. They are particularly recognized for their ability to promote elongation growth, which involves the lengthening of plant cells.

Role in Seed Germination

When it comes to seed germination, gibberellins trigger the synthesis of enzymes necessary for breaking down food reserves within the seed. This energy release is vital for the growth of the seedling. For example, in peanut seeds and potato tubers, gibberellins break the dormancy period, initiating the sprouting process.

Influence on Growth Patterns

Gibberellins also affect the directional growth patterns of plants. They are behind the horizontal growth and the characteristic 'hook' shape of the hypocotyl in dicot seedlings, which helps the seedling emerge from the soil and orient its leaves for efficient photosynthesis.

Understanding the actions of gibberellins assists in the agricultural sector by manipulating plant growth, improving yields, and controlling development stages.

Ethylene

Ethylene is a gaseous phytohormone known for its role in plant aging and response to stress. Unlike other plant hormones that are commonly transported in liquid form, ethylene diffuses as a gas through the spaces between the plant cells.

Accelerating Senescence

This hormone is renowned for its ability to hasten the senescence or aging process of plant cells. It acts as a signal for the onset of leaf fall (abscission) in deciduous trees and the shedding of petals after pollination in flowers. Ethylene is also involved in the ripening of fruits, making them softer and changing their color.

Managing Stress Responses

Additionally, ethylene mediates plant responses to environmental stresses and mechanical damage. For instance, when a plant is injured, ethylene can stimulate the formation of a protective scar tissue. Within agricultural systems, controlling ethylene levels offers opportunities to manage the shelf life of fruits and the timing of flowering in ornamentals.

Seed Dormancy

Seed dormancy is a survival strategy that prevents seeds from germinating under non-favorable conditions. Dormancy is a state of temporary inactivity in seeds, which ensures that germination only occurs when environmental conditions are ideal for seedling survival.

Breaking Dormancy

Gibberellins play a crucial role in breaking seed dormancy. They stimulate the production of enzymes that metabolize the stored food in seeds, empowering them with the necessary energy for growth. This process is essential for seeds, such as those of the peanut, which require these hormones to initiate germination.

It's important for students to comprehend the regulatory mechanisms behind seed dormancy and how they relate to natural cycles, as well as to agricultural practices like crop cultivation timing and improving germination rates of commercially important plants.

Plant Growth and Development

Plant growth and development encompasses all the stages from seed germination to senescence, regulated by a complex interplay of phytohormones. These substances act as chemical messengers that influence plant structure and adaptability to their environment.

Harmonious Collaboration

Phytohormones like gibberellins, ethylene, cytokinins, and abscisic acid (ABA) work together to manage growth direction, flowering, fruit ripening, and response to environmental stresses. Each hormone has distinct roles but often interacts with others, creating a finely balanced system that adjusts the plant's growth and development.

For instance, while gibberellins can promote growth and break dormancy, ABA typically acts to maintain dormancy under adverse conditions. Understanding these mechanisms provides insights for horticultural practices, such as optimizing conditions for plant growth, managing crop production, and developing strategies to mitigate the effects of climate change on plant life.