Triple Response Test of Ethylene

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Triple Response Test of Ethylene

The triple response is a characteristic growth response shown by etiolated (dark-grown) dicot seedlings when exposed to ethylene. It is widely used as a bioassay to detect ethylene activity in plants.

Components of the Triple Response

Ethylene induces three distinct changes in seedlings:

1. Inhibition of Stem (Hypocotyl) Elongation

  • Seedlings become shorter and thicker.

  • Normal cell elongation is suppressed.

  • This helps the seedling avoid mechanical damage in the soil.

2. Radial Swelling of the Hypocotyl

  • Stem increases in diameter (swollen appearance).

  • Caused by increased lateral expansion of cells.

  • Strengthens the seedling to push through soil.

3. Horizontal Growth / Apical Hook Formation

  • The apical hook becomes more pronounced or curvature increases.

  • Seedling exhibits horizontal or curved growth.

  • Helps protect the delicate shoot tip from damage while emerging from soil.

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