Question

Which of the following statements regarding gibberellins is incorrect? (a) \(\mathrm{GA}_{3}\) was one of the first gibberellins to be discovered. (b) All GA are acidic. (c) They increase the length of plant axis as in grapes, sugarcanes etc. (d) They promote senescence.

Short answer

The incorrect statement regarding gibberellins is (d) They promote senescence.

Step-by-step solution

Understanding Gibberellins

Gibberellins (GAs) are a large family of plant hormones that play a role in various plant processes, including growth regulation, stem elongation, germination, and flowering. Different gibberellins have been discovered over time.

Evaluating Statement (a)

Statement (a) claims that GA3 was one of the first gibberellins to be discovered. This is a factually correct statement, as GA3, also known as gibberellic acid, was one of the first GAs identified.

Evaluating Statement (b)

Statement (b) asserts that all GAs are acidic. This is also correct, as gibberellins are generally acidic plant hormones.

Evaluating Statement (c)

Statement (c) says they increase the length of the plant axis in grapes, sugarcanes, and other plants. This is a correct function of gibberellins, particularly GA3 which is often used to increase the size of fruits and length of stems.

Evaluating Statement (d)

Statement (d) claims that they promote senescence. This statement is incorrect. Gibberellins generally delay senescence (the aging process) and promote growth, although effects can vary with concentrations and stages of plant development.

Key concepts

Plant Hormones

Plant hormones are naturally occurring organic substances that play a pivotal role in regulating plant growth and development. Among these are gibberellins, auxins, cytokinins, abscisic acid, and ethylene. Gibberellins, specifically, are vital in promoting stem elongation, seed germination, and fruit development, among other functions. They work synergistically and sometimes antagonistically with other hormones to orchestrate the complex growth patterns observed in plants.

For students delving into plant biology, understanding how these hormones interplay to affect plant morphology and lifecycle is crucial. For example, gibberellins are often used in agriculture to improve crop yields by increasing fruit size or inducing seedless fruit production. But it's important to note that hormones must be used in precise concentrations to achieve the desired effect, as over-application may lead to undesirable outcomes.

Stem Elongation

Stem elongation is a critical phase in the lifecycle of a plant, where the stem grows in length. This process is significantly influenced by gibberellins, which are among the key hormones that stimulate cell division and elongation. In crops like grapes and sugarcane, growers often apply gibberellins to extend the plant axis, leading to longer stems and larger fruit clusters. This practice enhances not only the visual appeal but also the market value of the crops.

Students should note that stem elongation isn't solely reliant on gibberellins but also on environmental factors such as light, water, and temperature. Investigation into stem growth can provide insights into how external conditions and hormonal regulation can be optimized for agronomic success.

Plant Senescence

Plant senescence is the aging process that leads to the death of plant tissues or the entire plant. It is marked by a decline in photosynthesis, nutrient recycling, and eventually, the cessation of growth and productivity. Contrary to certain misconceptions, gibberellins typically delay the onset of senescence. By promoting growth and cell division, they help extend the functional lifespan of plant tissues.

Understanding senescence is vital for areas such as crop management and horticulture, where prolonging the productive phase of plants can significantly impact yields and quality. For instance, delaying leaf senescence in crops can extend the period of photosynthesis, thereby enhancing the growth period and improving the harvest. However, it's also a delicate balance, as the improper use of plant hormones can disrupt the plant's natural development and senescence patterns.