Simon Marweyi
Feb 2
Describe the biosynthesis and physiological mechanism of action of gibberellins?
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Feb 2
Gibberellins are a class of plant hormones that play a crucial role in various physiological processes, including seed germination, stem elongation, flowering, and fruit development. They are synthesized through a complex biosynthetic pathway and exert their effects by binding to specific receptors and initiating a cascade of molecular events.
Biosynthesis of Gibberellins:
The biosynthesis of gibberellins begins with the conversion of geranylgeranyl diphosphate (GGDP) into ent-kaurene, which is catalyzed by the enzyme ent-copalyl diphosphate synthase (CPS). This reaction occurs in the plastids of plant cells. Ent-kaurene is then converted into gibberellin A12-aldehyde through a series of enzymatic reactions, including cyclization, oxidation, and reduction.
Further modifications of gibberellin A12-aldehyde lead to the formation of various gibberellin compounds, such as gibberellin A20 and gibberellin A1. These modifications involve enzymes like ent-kaurene oxidase, ent-kaurenoic acid oxidase, and gibberellin 3-oxidase. The final step in the biosynthesis of gibberellins involves the conversion of gibberellin A1 into its active form, gibberellin A4, through the action of gibberellin 20-oxidase.
Physiological Mechanism of Action:
Gibberellins exert their effects by binding to specific receptors, known as gibberellin receptors or GID1 (Gibberellin Insensitive Dwarf 1). These receptors are located in the cytoplasm of plant cells. Upon gibberellin binding, the gibberellin-GID1 complex interacts with a protein called DELLA, which is a negative regulator of gibberellin signaling.
The interaction between gibberellin-GID1 and DELLA leads to the degradation of DELLA protein through the ubiquitin-proteasome pathway. This degradation releases the repression on gibberellin-responsive genes, allowing them to be expressed. The activation of these genes initiates various physiological responses, such as cell elongation, cell division, and the synthesis of enzymes involved in plant growth and development.
Gibberellins also interact with other signaling pathways, such as auxin and abscisic acid, to regulate plant growth and development. They can enhance the production of auxin, which promotes cell elongation, and antagonize the effects of abscisic acid, which inhibits seed germination and growth.
In summary, gibberellins are synthesized through a complex biosynthetic pathway and exert their effects by binding to specific receptors and initiating a cascade of molecular events. They regulate various physiological processes in plants, including seed germination, stem elongation, flowering, and fruit development.
Biosynthesis of Gibberellins:
The biosynthesis of gibberellins begins with the conversion of geranylgeranyl diphosphate (GGDP) into ent-kaurene, which is catalyzed by the enzyme ent-copalyl diphosphate synthase (CPS). This reaction occurs in the plastids of plant cells. Ent-kaurene is then converted into gibberellin A12-aldehyde through a series of enzymatic reactions, including cyclization, oxidation, and reduction.
Further modifications of gibberellin A12-aldehyde lead to the formation of various gibberellin compounds, such as gibberellin A20 and gibberellin A1. These modifications involve enzymes like ent-kaurene oxidase, ent-kaurenoic acid oxidase, and gibberellin 3-oxidase. The final step in the biosynthesis of gibberellins involves the conversion of gibberellin A1 into its active form, gibberellin A4, through the action of gibberellin 20-oxidase.
Physiological Mechanism of Action:
Gibberellins exert their effects by binding to specific receptors, known as gibberellin receptors or GID1 (Gibberellin Insensitive Dwarf 1). These receptors are located in the cytoplasm of plant cells. Upon gibberellin binding, the gibberellin-GID1 complex interacts with a protein called DELLA, which is a negative regulator of gibberellin signaling.
The interaction between gibberellin-GID1 and DELLA leads to the degradation of DELLA protein through the ubiquitin-proteasome pathway. This degradation releases the repression on gibberellin-responsive genes, allowing them to be expressed. The activation of these genes initiates various physiological responses, such as cell elongation, cell division, and the synthesis of enzymes involved in plant growth and development.
Gibberellins also interact with other signaling pathways, such as auxin and abscisic acid, to regulate plant growth and development. They can enhance the production of auxin, which promotes cell elongation, and antagonize the effects of abscisic acid, which inhibits seed germination and growth.
In summary, gibberellins are synthesized through a complex biosynthetic pathway and exert their effects by binding to specific receptors and initiating a cascade of molecular events. They regulate various physiological processes in plants, including seed germination, stem elongation, flowering, and fruit development.
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