Gibberellins (GA) are plant growth regulators made in young leaves, shoot tips, roots and seeds.Stem elongationGibberellins stimulate growth of the internodes (the parts of the stem between leaves) by promoting both cell division and cell elongation. Many dwarf plant varieties, such as dwarf peas, have a mutation that means they cannot make active gibberellin. Treating them with gibberellin makes them grow to normal height. In some plants, gibberellins also cause bolting, the rapid growth of a flowering stem.Seed germinationGibberellins are essential for the germination of seeds such as barley:1. The seed absorbs water, which activates the embryo.
2. The embryo releases gibberellin.
3. Gibberellin diffuses to the aleurone layer, a layer of cells around the endosperm.
4. In the aleurone cells, gibberellin switches on the genes for amylase and other hydrolytic enzymes. It does this by causing the breakdown of DELLA proteins, which normally block the transcription factors for these genes.
5. Amylase hydrolyses starch in the endosperm into maltose, and then glucose.
6. The embryo uses the glucose for respiration and growth.
Abscisic acid (ABA) has the opposite effect, keeping seeds dormant.Commercial uses- Brewers use gibberellins to speed up germination of barley and the production of maltose (malting).
- Sprayed on grapes, gibberellins make the stalks and fruit grow larger.
- Inhibitors of gibberellin synthesis are sprayed on cereal crops to keep their stems short, so they are less likely to fall over in wind and rain.
2. The embryo releases gibberellin.
3. Gibberellin diffuses to the aleurone layer, a layer of cells around the endosperm.
4. In the aleurone cells, gibberellin switches on the genes for amylase and other hydrolytic enzymes. It does this by causing the breakdown of DELLA proteins, which normally block the transcription factors for these genes.
5. Amylase hydrolyses starch in the endosperm into maltose, and then glucose.
6. The embryo uses the glucose for respiration and growth.
Abscisic acid (ABA) has the opposite effect, keeping seeds dormant.Commercial uses- Brewers use gibberellins to speed up germination of barley and the production of maltose (malting).- Sprayed on grapes, gibberellins make the stalks and fruit grow larger.
- Inhibitors of gibberellin synthesis are sprayed on cereal crops to keep their stems short, so they are less likely to fall over in wind and rain.