Gibberellin
Encyclopedia
Gibberellins are plant hormone
s that regulate growth and influence various developmental processes
, including stem elongation, germination
, dormancy
, flowering, sex expression
, enzyme induction, and leaf and fruit senescence
.
Gibberellin was first recognized in 1926 by a Japan
ese scientist, Eiichi Kurosawa, studying bakanae
, the "foolish seedling" disease in rice.
It was first isolated in 1935 by Teijiro Yabuta, from fungal strains (Gibberella fujikuroi
) provided by Kurosawa. Yabuta called the isolate gibberellin.
Interest in gibberellins outside of Japan began after World War II
. In the United States, the first research was undertaken by a unit at Camp Detrick
in Maryland, via studying seedlings of the bean Vicia faba
. In the United Kingdom, work on isolating new types of gibberellin was undertaken at Imperial Chemical Industries
. Interest in gibberellins spread around the world as the potential for its use on various commercially important plants became more obvious. For example, research that started at the University of California, Davis
in the mid-1960s led to its commercial use on Thompson seedless table grapes
throughout California by 1962. A known antagonist to gibberellin is Paclobutrazol
(PBZ), which in turn inhibits growth and induces early fruitset as well as seedset.
acids that are synthesized by the terpenoid pathway in plastids and then modified in the endoplasmic reticulum and cytosol until they reach their biologically-active form. All gibberellins are derived via the ent-gibberellane skeleton, but are synthesised via ent-kaurene. The gibberellins are named GA1....GAn in order of discovery. Gibberellic acid
, which was the first gibberellin to be structurally characterised, is GA3.
As of 2003, there were 126 GAs identified from plants, fungi, and bacteria.
Gibberellins are tetracyclic diterpene acids. There are two classes based on the presence of 19 carbons or 20 carbons. The 19-carbon gibberellins, such as gibberellic acid, have lost carbon 20 and, in place, possess a five-member lactone bridge that links carbons 4 and 10. The 19-carbon forms are, in general, the biologically active forms of gibberellins. Hydroxylation also has a great effect on the biological activity of the gibberellin. In general, the most biologically active compounds are dihydroxylated gibberellins, which possess hydroxyl groups on both carbon 3 and carbon 13. Gibberellic acid is a dihydroxylated gibberellin.
Gibberellins are involved in the natural process of breaking dormancy
and various other aspects of germination
. Before the photosynthetic apparatus develops sufficiently in the early stages of germination, the stored energy reserves of starch
nourish the seedling. Usually in germination, the breakdown of starch to glucose
in the endosperm
begins shortly after the seed is exposed to water. It is believed that gibberellins in the seed embryo signal starch hydrolysis
through inducing the synthesis of the enzyme α-amylase
in the aleurone cells. In the model for gibberellin-induced production of α-amylase, it is demonstrated that gibberellins (denoted by GA) produced in the scutellum
diffuse to the aleurone cells where they stimulate the secretion α-amylase. α-Amylase then hydrolyses starch, which is abundant in many seeds, into glucose that can be utilized in cellular respiration to produce energy for the seed embryo. Studies of this process have indicated that gibberellins cause higher levels of transcription
of the gene coding for the α-amylase enzyme, in order to stimulate the synthesis of α-amylase.
Gibberellins are produced in greater mass when the plant is exposed to cold temperatures. They stimulate cell elongation, breaking and budding, seedless fruits, and seed germination. They do the last by breaking the seed’s dormancy and acting as a chemical messenger. Its hormone binds to a receptor, and Ca
2+ activates the protein calmodulin
, and the complex binds to DNA, producing an enzyme to stimulate growth in the embryo.
A major effect of gibberellins is the degradation of DELLA
proteins, the absence of which then allows Phytochrome Interacting Factors to bind to gene promoters and regulate gene expression. It is speculated that gibberellins cause DELLAs to become polyubiquitin
ated and, thus, destroyed by the 26S proteasome
pathway.
Plant hormone
Plant hormones are chemicals that regulate plant growth, which, in the UK, are termed 'plant growth substances'. Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved...
s that regulate growth and influence various developmental processes
Biological process
A biological process is a process of a living organism. Biological processes are made up of any number of chemical reactions or other events that results in a transformation....
, including stem elongation, germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
, dormancy
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
, flowering, sex expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
, enzyme induction, and leaf and fruit senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
.
Gibberellin was first recognized in 1926 by a Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese scientist, Eiichi Kurosawa, studying bakanae
Bakanae
or bakanae disease, from the Japanese for "foolish seedling", is a disease that infects the rice plant. It is caused by the fungus Gibberella fujikuroi, whose metabolism produces a surplus of gibberellic acid. In the plant, this acts as a growth hormone, causing hypertrophy...
, the "foolish seedling" disease in rice.
It was first isolated in 1935 by Teijiro Yabuta, from fungal strains (Gibberella fujikuroi
Gibberella fujikuroi
Gibberella fujikuroi is a fungal plant pathogen. It causes bakanae disease in rice seedlings, by overloading them with the phytohormone gibberellin as its own metabolic byproduct.- External links :* * *...
) provided by Kurosawa. Yabuta called the isolate gibberellin.
Interest in gibberellins outside of Japan began after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. In the United States, the first research was undertaken by a unit at Camp Detrick
Fort Detrick
Fort Detrick is a U.S. Army Medical Command installation located in Frederick, Maryland, USA. Historically, Fort Detrick was the center for the United States' biological weapons program ....
in Maryland, via studying seedlings of the bean Vicia faba
Vicia faba
This article refers to the Broad Bean plant. For Broadbean the company, see Broadbean, Inc.Vicia faba, the Broad Bean, Fava Bean, Field Bean, Bell Bean or Tic Bean, is a species of bean native to north Africa and southwest Asia, and extensively cultivated elsewhere. A variety is provisionally...
. In the United Kingdom, work on isolating new types of gibberellin was undertaken at Imperial Chemical Industries
Imperial Chemical Industries
Imperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...
. Interest in gibberellins spread around the world as the potential for its use on various commercially important plants became more obvious. For example, research that started at the University of California, Davis
University of California, Davis
The University of California, Davis is a public teaching and research university established in 1905 and located in Davis, California, USA. Spanning over , the campus is the largest within the University of California system and third largest by enrollment...
in the mid-1960s led to its commercial use on Thompson seedless table grapes
Sultana (grape)
The sultana is a type of white, seedless grape assumed to originate from the Turkish, Greek, or Iranian area...
throughout California by 1962. A known antagonist to gibberellin is Paclobutrazol
Paclobutrazol
Paclobutrazol, PBZ is a plant growth retardant and triazole fungicide. It is a known opponent of the plant hormone gibberellin...
(PBZ), which in turn inhibits growth and induces early fruitset as well as seedset.
Chemistry
All known gibberellins are diterpenoidTerpenoid
The terpenoids , sometimes called isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in...
acids that are synthesized by the terpenoid pathway in plastids and then modified in the endoplasmic reticulum and cytosol until they reach their biologically-active form. All gibberellins are derived via the ent-gibberellane skeleton, but are synthesised via ent-kaurene. The gibberellins are named GA1....GAn in order of discovery. Gibberellic acid
Gibberellic acid
Gibberellic acid Gibberellic acid Gibberellic acid (also called Gibberellin A3, GA, and (GA3) is a hormone found in plants. Its chemical formula is C19H22O6. When purified, it is a white-to-pale-yellow solid....
, which was the first gibberellin to be structurally characterised, is GA3.
As of 2003, there were 126 GAs identified from plants, fungi, and bacteria.
Gibberellins are tetracyclic diterpene acids. There are two classes based on the presence of 19 carbons or 20 carbons. The 19-carbon gibberellins, such as gibberellic acid, have lost carbon 20 and, in place, possess a five-member lactone bridge that links carbons 4 and 10. The 19-carbon forms are, in general, the biologically active forms of gibberellins. Hydroxylation also has a great effect on the biological activity of the gibberellin. In general, the most biologically active compounds are dihydroxylated gibberellins, which possess hydroxyl groups on both carbon 3 and carbon 13. Gibberellic acid is a dihydroxylated gibberellin.
Gibberellins are involved in the natural process of breaking dormancy
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
and various other aspects of germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
. Before the photosynthetic apparatus develops sufficiently in the early stages of germination, the stored energy reserves of starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
nourish the seedling. Usually in germination, the breakdown of starch to glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
in the endosperm
Endosperm
Endosperm is the tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet...
begins shortly after the seed is exposed to water. It is believed that gibberellins in the seed embryo signal starch hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
through inducing the synthesis of the enzyme α-amylase
Amylase
Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...
in the aleurone cells. In the model for gibberellin-induced production of α-amylase, it is demonstrated that gibberellins (denoted by GA) produced in the scutellum
Scutellum (botany)
The scutellum is part of the structure of a barley seed—the modified seed leaf.The scutellum can also refer to the equivalence of a thin cotyledon in monocots...
diffuse to the aleurone cells where they stimulate the secretion α-amylase. α-Amylase then hydrolyses starch, which is abundant in many seeds, into glucose that can be utilized in cellular respiration to produce energy for the seed embryo. Studies of this process have indicated that gibberellins cause higher levels of transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
of the gene coding for the α-amylase enzyme, in order to stimulate the synthesis of α-amylase.
Gibberellins are produced in greater mass when the plant is exposed to cold temperatures. They stimulate cell elongation, breaking and budding, seedless fruits, and seed germination. They do the last by breaking the seed’s dormancy and acting as a chemical messenger. Its hormone binds to a receptor, and Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
2+ activates the protein calmodulin
Calmodulin
Calmodulin is a calcium-binding protein expressed in all eukaryotic cells...
, and the complex binds to DNA, producing an enzyme to stimulate growth in the embryo.
A major effect of gibberellins is the degradation of DELLA
Della
Della may refer to:* Della Alexander, a fictional character in the soap opera EastEnders* Della Street, the fictional secretary of Perry Mason* Della Duck, a fictional character and twin sister to Donald Duck* George W. Della, Jr...
proteins, the absence of which then allows Phytochrome Interacting Factors to bind to gene promoters and regulate gene expression. It is speculated that gibberellins cause DELLAs to become polyubiquitin
Ubiquitin
Ubiquitin is a small regulatory protein that has been found in almost all tissues of eukaryotic organisms. Among other functions, it directs protein recycling.Ubiquitin can be attached to proteins and label them for destruction...
ated and, thus, destroyed by the 26S proteasome
Proteasome
Proteasomes are very large protein complexes inside all eukaryotes and archaea, and in some bacteria. In eukaryotes, they are located in the nucleus and the cytoplasm. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks...
pathway.