Gibberellin

What do gibberellins affect the length of?

Internodes

• Regions between leaves on a stem

How were gibberellins discovered

Were produced from genus Gibberella that affects rice

• Infected seedlings grew extremely tall & thin

• Scientists isolated gibberellins

  • Which produces same spindly growth in plants, then discovered plants produce it themselves

What is the effect of no gibberellins in plants?

Plant stems are much shorter

• Reduces waste & makes plants less vulnerable to damage by weather & harvesting

How can gibberellins be used commercially ?

• Can be used to delay ripening & ageing in fruits

• Improve size & shape of fruits

• In beer brewing, to speed up malting process

Experimental evidence - germinating seeds & gibberellin

Mutant varieties of seeds have been bred which lack gene enabling them to make gibberellin

• Seeds don’t germinate

Gibberellin biosynthesis inhibitors applied to seeds

• Don’t germinate as gibberellin isn’t produced for them to break dormancy

Seed germination process

When conditions right:

1. Seed absorbs water

2. Stimulates embryo to prod. gibberellins

3. G molecules diffuse into aleurone layer, stimulates cells to synthesise amylase

4. Amylase hydrolyses starch in endosperm, producing maltose

5. Maltose → glucose, transported to embryo

6. Glucose respired by embryo, breaks dormancy, provides embryo w. energy needed for growth