Auxins: Types, Sources & Applications — NEET Biology
📚 Practice ConceptAuxins (from Greek 'auxein': to grow) was first isolated from human urine. The term 'auxin' is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth regulating properties. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. Auxins like IAA and indole butyric acid (IBA) have been isolated from plants. NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins. All these auxins have been used extensively in agricultural and horticultural practices.
Which of the following statements about Auxins are correct? S1. Indole-3-acetic acid (IAA) and indole butyric acid (IBA) are natural auxins, while NAA and 2,4-D are synthetic auxins. S2. Auxins are primarily produced in root apices and mature leaves, from where they regulate growth. S3. They prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits. S4. In higher plants, the growing apical bud promotes the growth of lateral buds, a phenomenon known as apical dominance. S5. Auxins are capable of inducing parthenocarpy, as seen in tomatoes. S6. They help to initiate rooting in stem cuttings, making them useful in plant propagation.
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Correct answer: A — S1, S3, S5 and S6
The question asks to select the correct statements regarding Auxins. S1. The term ‘auxin’ is applied to IAA, and IAA and IBA have been isolated from plants (natural). NAA (naphthalene acetic acid) and 2,4-D (2,4-dichlorophenoxyacetic) are synthetic auxins. This statement is correct. S2. Auxins are generally produced by the *growing apices of the stems and roots*, not primarily in root apices and *mature leaves*. Therefore, this statement is incorrect. S3. Auxins help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits. This statement is correct. S4. In most higher plants, the growing apical bud *inhibits* the growth of the lateral (axillary) buds, which is called apical dominance. The statement says it *promotes* lateral bud growth. Therefore, this statement is incorrect. S5. Auxins induce parthenocarpy, e.g., in tomatoes. This statement is correct. S6. Auxins help to initiate rooting in stem cuttings, an application widely used for plant propagation. This statement is correct. Therefore, statements S1, S3, S5, and S6 are correct. Option A correctly identifies all the true statements.
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