SNHS Biology Blog 12: Gibberellins

Shriya Mahakala

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What Are Gibberellins?

Gibberellins are a group of plant hormones that help in development processes such as flowering and stem elongation. They are synthesized in plastids which are organelles in plant cells responsible for making food.

How Were Gibberellins Discovered?

Gibberellins were discovered during World War 2 in Japan. A Japanese botanist was studying the Baknae (foolish seedling) disease that has been damaging rice cultivation since forever. The symptoms of the disease were found to be caused by toxin created by the Baknae fungus. The toxins were studied and labeled Gibberellins A and B. Soon after the war, these findings gained attention from all over the world and many scientists started to identify gibberellins in other plant species. They were later categorized as a group of plant hormones and as of today, scientists have identified 112 different gibberellins!

How Do Gibberellins Work?

The signaling pathway of gibberellins is believed to be autocrine meaning that the gibberellin acts on the same cell that produces it. The gibberellin first binds to the receptor protein on the membrane, causing the receptor to change shape. This activates a seperate G protein because it causes the GDP attached to the G protein to be replaced with GTP. The G protein releases cyclic GMP which acts as a second messenger. A second messenger is a small molecule or ion that relays signals received by the receptor protein to other proteins. cGMP activates an F-box protein. The activated F-box protein then binds to the DELLA protein which is a repressor protein that obstructs the transcription of a GAMYB gene. The repressor is degraded allowing for the GAMYB protein to be synthesized and then bind to promoters of certain genes that encode hydrolytic enzymes like a-amylase. This causes these genes to be transcribed and the hydrolytic enzymes to be synthesized on the rough ER. The proteins are released out the cell to break down starch and provide energy for different development processes.

Gibberellins Use In Farming

Since gibberellins are responsible for growth and development in plants, farmers grow a fungus that produces large quantities of the plant hormones. They then use the produced gibberellins to grow their own produce to large sizes or increase fruit production. The gibberellins can even be used to restrict flowering in fruit tree orchids so the trees have more time to grow. In addition, the group of plant hormones can be used to treat dwarfed plants or prevent trees from getting plant viruses transmitted by pollen. As you can see, the discovery of gibberellins has played a great part in improving farming.