|Molar mass||346.37 g/mol|
|Melting point||233 to 235 °C|
|Solubility in water||5 g/l (20 °C)|
The first step into the understanding of Gibberellins was the developments from the plant pathology field, with research on the bakanae, or "foolish seedling" sickness in rice. Foolish seedling illness causes a solid elongation of rice stems and leaves and ultimately causes them to collapse over. Japanese scientist Eiichi Kurosawa revealed that foolish seedling disease was caused by the fungus Gibberella fujikuroi, in early years of 1926. Later work at the University of Tokyo (notable from Yabuta, Sumiki, and Hayashi) displayed that a substance created by this fungus caused the symptoms of the foolish seedling disease and they coined this substance ‘gibberellin’.
As we all aware of gibberellins are diterpenoid acids that are produced by the terpenoid pathway in plastids and then altered in the endoplasmic reticulum and cytosol until they reach their biologically-active level. All gibberellins are derived from the ent-gibberellin skeleton but are produced via ent-kaurene. The gibberellins are so-called GA1 through GAn in order of detection. Gibberellic acid, which was the first gibberellin to be fundamentally characterized, is GA3.
GA1, GA3, GA4, and GA7 are bioactive GAs. There are three basic structural characters among these GAs:
Most bioactive gibberellins are situated in actively growing organs on plants. Each GA3ox and GA20ox genes (genes coding for GA 3-oxidase and GA 20-oxidase) and the SLENDER1 gene (a GA sign transduction gene) are seen in growing organs on rice, which proposes bioactive gibberellins synthesis happens at their site of action in growing organs of plants. Throughout flower development, the tapetum of anthers is supposed to be a primary site of gibberellins biosynthesis.
A plant Arabidopsis and a fungus “Gibberellafujikuroi” have different gibberellins pathways and enzymes. P450s in fungi do functions analogous as compared to functions of KAOs in plants. The role of CPS and KS in plants is done by a single enzyme, CPS/KS. In fungi, the gibberellins biosynthesis genes are present on one chromosome, but in plants, they are found casually on multiple chromosomes. Plants yield a low amount of GA3, hence the GA3 is made for industrial uses by microorganisms. For industrial use, the gibberellic acid can be manufactured by submerged fermentation, but this process presents low production with high production costs and therefore higher sale value, however, another alternative process to decrease costs of the GA3 making is Solid-State Fermentation (SSF) that lets the use of agro-industrial residues.
Numerous mechanisms for inactivating gibberellins have been recognized. 2β-hydroxylation disables GA and is catalyzed by GA2-oxidases (GA2oxs). Certain GA2oxs use C19-GAs as substrates, and others GA2oxs use C20-GAs. Cytochrome P450 mono-oxygenase, determined by elongated highest internode (eui), transforms GAs into 16α, 17-epoxides. Rice eui mutants amass bioactive gibberellins at high levels, which suggests cytochrome P450 mono-oxygenase is a key enzyme is responsible for deactivation gibberellins in rice. The Gamt1 and gamt2 genes convert enzymes that methylate the C-6 carboxyl group of gibberellins. In a gamt1 and gamt2 mutant, amount of gibberellins is developing seeds is increased.
Feedback and feedforward parameter keeps the levels of bioactive gibberellins in plants. Levels of AtGA20ox1 and AtGA3ox1 expression are improved in a gibberellins deficient environment and reduced after the addition of bioactive gibberellins. Equally, the expression of AtGA2ox1 and AtGA2ox2, gibberellins deactivation genes, is improved with the addition of gibberellins.
The auxin indole-3-acetic acid (IAA) controls the concentration of GA1 in getting longer internodes in peas. Removal of IAA by removal of the apical bud, the auxin source, decreases the amount of GA1, and reintroduction of IAA reverses these effects to raise the amount of GA1. This process has also been observed in tobacco plants. Auxin surges GA 3-oxidation and drops GA 2-oxidation in barley. Auxin also controls gibberellins biosynthesis during fruit growth in peas. These detections in different plant species explain the auxin regulation of gibberellins metabolism may be a common mechanism.
Bioactive gibberellins and abscisic acid levels have an opposite relationship and regulate seed germination and development. Levels of FUS3, an Arabidopsis transcription aspect, are unregulated by ABA and down-regulated by gibberellin, which proposes that there is a regulation loop that creates the balance of gibberellin and ABA.