Unformatted text preview: Plant Growth Regulators - 18 • Ethylene functions to help germinating seeds overcome mechanical stress. A shoot tip that encounters an immovable object will grow around the object by changing its growth direction. This occurs through differential elongation of cell walls. When the shoot tip cannot penetrate the mechanical obstacle, ethylene is synthesized, which slows cell wall expansion. The walls thicken (more resistant to the pressure) and the stem curves to bypass the obstacle via horizontal growth. (Essentially the shoot is growing around the obstacle.) The stem tip pushes upward periodically to test for the obstacle. If the obstacle is encountered, ethylene initiates another cycle of stem thickening and horizontal growth. If no obstacle is encountered, the shoot resumes negative geotropic growth. This growth response is known as the triple response (decrease in elongation, stem thickening, and change in orientation of shoot growth to horizontal)....
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This note was uploaded on 01/08/2012 for the course BIO 213 taught by Professor Makina during the Fall '09 term at SUNY Stony Brook.
- Fall '09