Question

Which of the following PGR is widely used as herbicide? (a) Auxin (b) Gibberellic acid (c) Cytokinins (d) All of these

Short answer

The PGR widely used as a herbicide is (a) Auxin

Step-by-step solution

Understanding Plant Growth Regulators Functions

To answer this question, it is important to know the functions of each plant growth regulator. Auxins are involved in cell elongation, apical dominance, and rooting. Gibberellic acids stimulate stem elongation, germination, and flowering. Cytokinins promote cell division, shoot initiation and growth, delay leaf senescence.

Understanding Herbicides

Herbicides are substances that are used to control unwanted plants and weeds. They work by stopping or slowing plant growth.

Matching PGRs with Herbicides

Based on the functions of the PGRs, Auxin is the only one that seems like it could potentially act as a herbicide, since it inhibits growth in places where it's not needed (like in the case of weeds).

Key concepts

Auxin as Herbicide

Auxin, a well-known plant growth regulator, has a significant impact on plant development by promoting cell elongation, apical dominance, and root initiation. Interestingly, when applied in high concentrations, auxin can act as a herbicide, causing abnormal and uncontrolled growth that leads to plant death. This happens because excessive auxin levels disrupt normal plant growth processes, which can lead to the deformed growth of roots and shoots, ultimately killing the plant.

Herbicides based on auxin are commonly used to target broadleaf weeds, leaving grass and other monocot plants relatively unaffected. The selective nature of auxin herbicides makes them particularly useful in lawns and cereal crops. Farmers and gardeners apply auxin herbicides to control unwanted weeds without harming their crops, showcasing the vital role of understanding plant physiology in agriculture.

Functions of Plant Growth Regulators

Plant growth regulators (PGRs) are chemicals that influence the growth and development of plants, and they are integral to plant physiology. They can be natural or synthetic and are used to manage plant growth in various ways. The primary functions of PGRs include:

• Auxins: They stimulate cell elongation, promote root formation, and are involved in the regulation of fruit development.
• Gibberellins: These are crucial for stem elongation, seed germination, and flowering. They also break seed dormancy and stimulate enzyme production for germination.
• Cytokinins: They encourage cell division, chloroplast development, and delay the aging of plant tissues. Cytokinins are involved in shoot initiation and growth.

Each PGR plays a distinct role in plant growth, and understanding these functions can aid in identifying their potential as herbicides or other applications in agricultural practices.

Herbicide Mechanism

Herbicides operate through various mechanisms to eliminate or suppress weed growth. They can be selective, targeting specific types of plants, or non-selective, affecting nearly all vegetation they contact. Herbicides function in different ways:

• Contact herbicides: These kill only the plant tissue that they touch, and are effective at managing annual weeds.
• Systemic herbicides: These are absorbed and transported within the plant, leading to the death of the entire organism – root and shoot. Auxin-like herbicides often fall under this category.
• Pre-emergent herbicides: Applied to the soil, these chemicals control weeds before they emerge by inhibiting seed germination or early growth.

Understanding how these chemicals act at the physiological level is essential to using them effectively and safely. Overuse or misuse of herbicides can lead to environmental damage and the emergence of herbicide-resistant weed strains, underscoring the importance of knowledgeable application.