Question

Select the correct statement(s) regarding auxins. (a) Auxins promote root growth only at extremely low concentrations and they inhibit root growth at higher concentrations. (b) Concentration of auxins which is inhibitory to root growth causes initiation of adventitious roots from the nodes or basal regions of stem. (c) Auxins such as NAA and IBA are used to induce rooting in stem cuttings. (d) All of these.

Short answer

All the statements (a), (b), and (c) regarding auxins are correct; therefore, the correct statement is (d) All of these.

Step-by-step solution

Understanding Auxins and Their Effects at Different Concentrations

Examine the effects that auxins (a class of plant hormones) have on root growth at various concentrations. Auxins do promote root growth at very low concentrations, but they can inhibit root growth when the concentration is too high.

Analyzing the Effects of Auxins on Adventitious Roots

Consider how auxins influence the growth of adventitious roots, which are roots that develop from parts of the plant other than the root, such as nodes or the base of the stem, particularly when they are present at concentrations that are inhibitory to the primary root growth.

Assessing the Use of Synthetic Auxins

Evaluate the practical application of synthetic auxins like NAA (Naphthaleneacetic acid) and IBA (Indole-3-butyric acid), which are commonly used to stimulate the root growth in stem cuttings, a technique used in plant propagation.

Identifying the Correct Statements

Identify which of the provided statements are true in relation to the known effects and uses of auxins in plant growth and development.

Key concepts

Auxins Root Growth Concentration

Auxins, a family of plant hormones, play a pivotal role in influencing root development. At very low concentrations, auxins can stimulate root growth by elongating the cells in the root. This intricate balance is crucial for plant vigor and stability. However, if the concentration of auxins increases beyond an optimal threshold, they have the opposite effect. High auxin levels essentially put the brakes on root elongation and can even halt the process.

Understanding this concentration-dependent behavior is vital for both natural plant development and agricultural practices. For instance, in tissue culture methods, the precise regulation of auxin concentrations can determine the success of root formation in cloned plants. Too much or too little can lead to poor rooting, thus affecting the overall health and productivity of the plant.

Adventitious Root Initiation

Adventitious roots are an intriguing aspect of plant biology, referring to roots that emerge from non-root tissues such as stems, leaves, or old roots. One of their most notable features is how they can be initiated by auxins under specific circumstances. When the concentration of auxins is too high for normal root growth, rather than promoting growth in the existing root system, these hormones can trigger the formation of new root structures from unexpected places.

Adventitious rooting is particularly beneficial in scenarios like when a plant is damaged and needs to establish new roots to absorb water and nutrients rapidly. Moreover, this phenomenon is expertly harnessed in horticulture to propagate new plants from cuttings. By applying auxins to the cut ends of stems or leaves, gardeners can encourage the formation of new roots, effectively cloning the plant.

Synthetic Auxins Plant Propagation

In a fusion of nature and science, the use of synthetic auxins, such as NAA (Naphthaleneacetic acid) and IBA (Indole-3-butyric acid), has revolutionized plant propagation. These man-made molecules mimic the effects of natural auxins and are employed to stimulate root growth in plant cuttings. Plant enthusiasts and commercial growers alike rely on these synthetic auxins to ensure the consistent and reliable development of new plants.

Applying these compounds to the base of cuttings initiates root development, making the process of cloning plants more efficient and successful. The ability to control the concentration and application of synthetic auxins provides an incredible tool to propagate a vast array of plant species, which is invaluable for agriculture, horticulture, and conservation efforts.