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Difficulty: HardPlant Science and Agricultural Technology

Consider the following statements regarding plant growth regulators and their technological applications in agriculture and tissue culture:

1. In plant tissue culture micropropagation, a high ratio of auxin to cytokinin promotes root organogenesis (rhizogenesis), whereas a high ratio of cytokinin to auxin promotes shoot bud differentiation (caulogenesis).
2. Synthetic auxins such as 2,4-Dichlorophenoxyacetic acid (2,4-D) act as selective herbicides by inducing lethal abnormal growth in broad-leaved dicotyledonous weeds while leaving monocotyledonous cereal crops unaffected.
3. Ethephon hydrolyzes within plant cells to release ethylene gas, which is applied in commercial agriculture to synchronize fruit ripening and induce female flower development in cucurbit crops.

Which of the statements given above are correct?

  1. A
    1 and 2 only
  2. B
    2 and 3 only
  3. C
    1 and 3 only
  4. 1, 2 and 3Answer

Answer

All three statements (1, 2, and 3) are correct.
The correct answer includes all three statements because each accurately describes a established biological and technological application of plant hormones. Statement 1 correctly reflects the Skoog-Miller model of organogenesis in micropropagation, Statement 2 accurately describes the selective action of synthetic auxin 2,4-D on broad-leaved dicot weeds in cereal fields, and Statement 3 correctly details the ethylene-releasing mechanism of ethephon in horticultural crop management.

Step-by-Step Solution

1
Evaluate Statement 1 on hormonal balance in tissue culture organogenesis.
Skoog and Miller established that morphogenesis in callus cultures is controlled by the ratio of auxin to cytokinin: a high auxin:cytokinin ratio promotes rhizogenesis (root formation), a high cytokinin:auxin ratio promotes caulogenesis (shoot formation), and an intermediate ratio promotes callus proliferation. Statement 1 is correct.
Verify physiological principles of plant tissue culture micropropagation.
2
Evaluate Statement 2 on synthetic auxin selectivity as a herbicide.
2,4-D is a synthetic auxin that acts as a selective herbicide. Dicotyledonous plants absorb and translocate it rapidly, causing unsustainable metabolic strain, vascular collapse, and uncontrolled stem elongation, whereas monocotyledonous crops (like wheat, rice, and corn) metabolize and inactivate it rapidly or have resistant vascular anatomy. Statement 2 is correct.
Verify chemical weed management mechanisms in agricultural science.
3
Evaluate Statement 3 on ethephon and ethylene action in horticulture.
Ethephon (2-chloroethylphosphonic acid) breaks down into ethylene, phosphate, and chloride ions at plant physiological pH. Ethylene triggers climacteric fruit ripening and alters floral development towards female flower production in cucurbits. Statement 3 is correct.
Verify post-harvest and developmental applications of plant growth regulators.

Key Concept

Plant Growth Regulators and Agronomic Applications
Estimated Time:2m 0s
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Topics

Plant Science and Agricultural Technology

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