Give a detailed account of auxins and gibberellins as plant growth regulators -- covering, for each, how it was discovered, its principal natural source within the plant, and at least three of its major physiological effects, including at least one commercial or agricultural appl

Question

Give a detailed account of auxins and gibberellins as plant growth regulators -- covering, for each, how it was discovered, its principal natural source within the plant, and at least three of its major physiological effects, including at least one commercial or agricultural application.

Accepted Answer

Auxin's discovery traces back to Charles and Francis Darwin's observation that a canary-grass coleoptile bends toward unilateral light only if its very tip is intact, implying the tip perceives light and transmits an influence downward; Boysen-Jensen later showed this influence could cross a gelatin block but not an impermeable mica barrier, proving it was a diffusible chemical rather than an electrical signal; and F. W. Went finally isolated the substance itself, placing excised oat coleoptile tips asymmetrically on agar blocks and showing that the agar block alone, applied off-centre to a decapitated coleoptile in complete darkness, still produced bending -- naming the responsible chemical auxin. The principal natural auxin is indole-3-acetic acid (IAA), synthesised chiefly in the shoot apex and young, actively growing leaves. Its physiological effects are wide-ranging: it promotes cell elongation, most visibly in the phototropic bending with which its discovery story began; it maintains apical dominance, suppressing lateral bud growth for as long as the apical bud remains active (removing the apical bud releases the lateral buds, as gardeners exploit when 'pinching out' a shoot); it promotes adventitious root initiation, which is why auxin-based rooting powders are used commercially on stem cuttings; and the synthetic auxin 2,4-D is widely used as a selective herbicide against dicot weeds in cereal fields, since it disrupts dicot growth at concentrations cereal (monocot) crops tolerate well. …

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Q.Give a detailed account of auxins and gibberellins as plant growth regulators -- covering, for each, how it was discovered, its principal natural source within the plant, and at least three of its major physiological effects, including at least one commercial or agricultural application.

Concept understanding — Auxin

Q.Give a detailed account of auxins and gibberellins as plant growth regulators -- covering, for each, how it was discovered, its principal natural source within the plant, and at least three of its major physiological effects, including at least one commercial or agricultural application.

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