Controlling Plant Growth Flashcards
Define apical dominance.
Inhibition of lateral buds further down the shoot by chemicals produced by the apical bud at the tip of the plant shoot.
What are auxins?
Plant hormones which are responsible for regulating plant growth.
What are gibberellins?
Plant hormones which are responsible for control of stem elongation and seed germination.
What happens if you break the shoot tip off of a plant?
The plant starts to grow side branches from lateral buds that were previously dormant.
What did the research into auxins suggest?
That the auxins form the apical bud prevent buds from growing. When the tip is removed, auxin levels in the shoot drop and the buds grow.
A normal level of auxin in lateral buds inhibits growth whereas low auxin levels promote growth.
How did scientists test their hypothesis about auxins?
They applied a paste containing auxins to the cut end of a shoot, and the lateral buds did not grow.
What happened when scientist applied a ring of auxin inhibitor to the apex of a shoot?
The lateral buds were able to grow. This is because the shoots were exposed to oxygen and were therefore able to produce the hormone that promoted lateral bud growth.
What does abscisic acid do and how does auxin link in?
It inhibits bud growth. High auxin in the shoot may keep abscisic levels high in the bud. When the tip is removed, abscisic acid levels drop and the bud starts to grow.
What do cytokinins do?
They promote bud growth - directly applying cytokinins to buds can override the apical dominance effect. High levels of auxin make the shoots of plants a sink for cytokinins produced in the roots.
What happens to cytokinins when the apex is removed?
It spreads evenly around the plant.
What happened to rosette plants such as cabbages when gibberellins were added?
They grew really tall.
How was gibberellic acid discovered?
It was discovered as a fungus in rice plants which caused them to grow really tall.
How do gibberellins cause stem elongation?
Gibberellins cause stem elongation by loosening cell walls and increase cell division by stimulating production of a protein that controls the cell cycle.
How do gibberellins promote seed germination?
When the seed absorbs water, the embryo releases gibberellin, which travels to the aleurone layer in the endosperm region of the seed. The gibberellin enables the production of amylase, which can break down starch into glucose. This provides a substrate for respiration for the embryo and so it grows.
What is the synthesis pathway for gibberellins?
ent-kaurene -> GA12-aldehyde -> GA12 -> GA53 -> GA 44 -> GA19 -> GA 20 + enzyme produced by Le allele -> GA1
