QUESTION: Which of the following is not a plant hormone?
A Auxin
B Ascorbic acid
C Cytokinin
D Abscisic acid
ANSWER: Ascorbic acid
| Hormone | Chemical Formula | Origin | Function |
| Auxins | C₁₉H₂₂O₆ | · Apical meristem · Young leaves | · Promotes cell elongation · Controls root and shoot growth · Influences tropisms (phototropism, gravitropism) |
| Cytokinins | Various | · Root tips · Developing fruits | · Promotes cell division and differentiation · Delays the process of aging · Influences apical dominance |
| Gibberellins | C₁₉H₂₂O₆ | · Young leaves · Stems · Roots | · Stimulates stem elongation · Seed germination · Fruit growth · Breaks seed dormancy |
| Abscisic Acid | C₁₅H₂₀O₄ | · Leaves · Stems · Roots | · Induces dormancy and stress responses · Inhibits growth · Regulates stomatal closure |
| Ethylene | C₂H₄ | · Various tissues | · Promotes fruit ripening and abscission · Inhibits stem elongation · Influences senescence |
| Brassinosteroids | Various | · Pollen · Young leaves · Stems | · Promote cell elongation and division · Enhance stress tolerance · Promote vascular differentiation |
| Jasmonates | C₁₂H₁₁NO₂ | · Wounded tissues · Leaves | · Mediate defense responses against herbivores and pathogens · Regulate root growth |
| Salicylic Acid | C₇H₆O₃ | · Various tissues | · Induces systemic acquired resistance against pathogens · Regulates plant defense |
| Strigolactones | Various | · Roots · Root exudates | · Suppress lateral bud growth · Promote mycorrhizal associations · Inhibit shoot branching |
| Polyamines | Various | · Various tissues | · Involved in cell growth and differentiation · Influence stress responses and flowering |