Gibberellins
ஜிபெரலின்கள்
Stop confusing Gibberellins with Auxins. Auxins promote apical dominance; Gibberellins break the genetic dwarfism of plants. If you miss this distinction, you lose 4 marks on a basic physiology question.
The idea
Gibberellins are acidic Plant Growth Regulators (PGRs) that stimulate internodal elongation. They induce bolting—internode elongation just prior to flowering—in rosette plants like cabbage and beet. In agriculture, they are applied to increase the length of grape stalks and boost sugarcane yield by increasing internode length. They are essential for breaking seed dormancy and promoting fruit set.
Why it matters
They exist to regulate internode elongation and seed germination, allowing plants to adapt their height and reproductive timing to environmental conditions.
NEET lens
NEET focuses on the 'Bolting' and 'Sugarcane yield' applications. Expect matching-type questions linking PGRs to their specific physiological effects. Never confuse Gibberellins with Ethylene or Abscisic Acid. Memorize the specific examples: Grapes, Sugarcane, Cabbage, and Beet.
Clinical significance
Gibberellins are structurally related to ent-gibberellane rings, similar to the steroid backbone in human cholesterol and hormones. While plants use them for growth, humans lack these specific receptors. However, the study of these pathways is crucial for understanding how plant-derived compounds interact with human endocrine systems.
Introduction
Gibberellins (GAs) are a family of diterpenoid plant hormones that promote stem elongation, seed germination, fruit development, and flowering, first discovered from the fungus Gibberella fujikuroi.
Core concept
Discovery: Bakanae ('foolish seedling') disease of rice caused by Gibberella fujikuroi → plants grow abnormally tall. Kurosawa (1926) isolated the active compound — gibberellin. Over 100 gibberellins identified (GA1, GA3...). Key effects: Stem elongation (bolting) — dramatic elongation of internodes. Seed germination — induces α-amylase in aleurone layer of seeds → starch breakdown → seedling growth. Fruit development — seedless fruits (parthenocarpy) in grapes when sprayed with GA. Flowering — long-day plants can flower in short days if given GA (substitutes for vernalization).
Go deeper
GA and seed germination: GA released from embryo → travels to aleurone layer → activates genes for hydrolytic enzymes (α-amylase, proteases) → starch and proteins in endosperm hydrolyzed → sugars and amino acids released → fuel embryo growth. ABA antagonizes this: high ABA = dormancy, high GA = germination.
From Class 10
Some plants grow abnormously tall under certain conditions. Scientists discovered a fungal disease that caused this 'foolish seedling' disease — the culprit was a hormone called gibberellin.