Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promot

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Q. Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth, flowering and rooting. Explain the meaning of the following terms related to auxins. a. auxin precursors b. anti-auxins c. synthetic auxins

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Concept understanding — Auxins

Auxins — The Plant's Growth Director

Imagine a plant growing toward sunlight. Somewhere inside, there must be a signal that tells the shaded side to stretch longer, bending the stem toward the light. That signal is auxin.

Auxins are the first plant hormones ever discovered, and they are the master regulators of cell elongation. The most common natural auxin is Indole-3-Acetic Acid (IAA). It is produced primarily in the shoot apical meristem — the growing tip of the stem — and moves downward, controlling how the plant grows and responds to its environment.

What auxins actually do

The core action of auxin is simple: it makes plant cells expand lengthwise. But because it moves directionally (from tip to base, and away from light), it creates patterns of growth that shape the entire plant.

Apical dominance is a classic example. The terminal bud produces auxin, which travels down the stem and suppresses the growth of lateral (side) buds. This keeps the plant growing tall and straight. If you cut off the tip, auxin production stops, and the side buds finally get their chance — the plant becomes bushier. Gardeners and farmers exploit this when they prune.

Rooting works differently. At low concentrations, auxin actually promotes root formation. That is why commercial rooting powders contain synthetic auxins like IBA (Indole-3-Butyric Acid) — dip a cutting in it, and roots form faster.

Prevention of abscission (leaf and fruit drop) is another role. Auxin keeps the abscission layer — a zone of weak cells at the base of the leaf stalk — from forming. As long as enough auxin flows from the leaf into the stem, the leaf stays attached. When auxin levels drop (due to age or stress), the abscission layer develops and the leaf falls.

Auxin (IAA) at low concentration promotes cell elongation and root initiation. The same auxin (IAA) at high concentration inhibits lateral bud growth and can even inhibit root growth. Concentration, not just presence, decides the outcome.

The mechanism — how auxin makes cells grow

Auxin activates a proton pump in the cell membrane, pumping H⁺ ions into the cell wall. This acidifies the wall, activating enzymes called expansins that loosen the cellulose fibres. The cell wall becomes more flexible, and water enters by osmosis, inflating the cell. This is called the acid growth hypothesis. …

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Natural auxins like IAA/IBA occur in the plant itself, synthetic auxins like NAA/2,4-D are lab-made compounds with the same growth-regulating activity, and anti-auxins are substances that work against auxin's normal effects.

Auxin, from the Greek "auxein" meaning "to grow," is a term applied broadly to indole-3-acetic acid (IAA) and to other natural and synthetic compounds sharing certain growth-regulating properties.

a. Auxin precursors refers to the natural compounds isolated directly from plants that carry authentic auxin activity — IAA and indole butyric acid (IBA) are the examples that have been isolated from plant tissue itself. IAA in particular was first isolated (interestingly) from human urine before being confirmed as the natural plant auxin.

b. Anti-auxins are substances that act in opposition to auxin — that is, they interfere with or block the normal growth-promoting action that auxin has, rather than reproducing it. This stands in contrast to both natural and synthetic auxins, all of which reinforce auxin-type activity. …

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Q.Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth, flowering and rooting. Explain the meaning of the following terms related to auxins.
a. auxin precursors
b. anti-auxins
c. synthetic auxins

Concept understanding — Auxins

Auxins — The Plant's Growth Director

What auxins actually do

The mechanism — how auxin makes cells grow

Method: Classifying a Named Plant Growth Regulator by Its Origin

Steps

Q.Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth, flowering and rooting. Explain the meaning of the following terms related to auxins. a. auxin precursors b. anti-auxins c. synthetic auxins

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Q.Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth, flowering and rooting. Explain the meaning of the following terms related to auxins.
a. auxin precursors
b. anti-auxins
c. synthetic auxins

Unlock everything free for 14 days