Gibberellin

From Free net encyclopedia

Image:GA452DII.png Gibberellins are a plant growth substance (phytohormone) involved in promotion of stem elongation, mobilisation of food reserves in seeds and other processes. Its absence results in the dwarfism of some plant varieties. Chemically all known gibberellins are gibberellic acids, a family of diterpene 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.

Much of our knowledge of the biosynthesis and molecular mechanisms of gibberellins comes from research on their role in triggering α-amylase release by the aleurone layer in seed germination.

Gibberellin was first isolated in 1926 by Japanese scientists. It was derived from the Gibberella fungus lamapitus.

Examples: Gibberellin 452D

[edit]

Location, Characteristics and Occasions for Synthesis Induction

Synthesized in the embryo and germinating seeds
Synthesized in the roots
Increased in production in the dark when sugar cannot be manufactured, and decreased in production in the light
Synthesized in apical meristems ? and young leaves ?
Produced in the stem rather than the growing tip ? (opposite finding to above – conflicting sources)
Transported in non-polar, bidirectional manner, producing general responses
Released in all cells (more particularly root and mature cells) when they do not have enough sugar and oxygen to support both themselves and any dependent cell (speculative)
Released in response to root, environmental, pest, and disease stress
Directly induced by high levels of CK (speculative)

[edit]

Effects

Stimulates shoot and cell elongation
Delays senescence of leaves
Inhibits root growth
Inhibits adventitious root growth
Produces seed germination
Antagonist promotes root growth and GA reverses this
Promotes root initiation in low concentration in pea cuttings
Stimulates bolting and flowering in biennials
Regulates production of hydrolytic enzymes for digesting starches
Inhibits CK bud growth on calluses
Inhibits bud formation
Inhibits leaf formation
Breaking of dormancy
Induces extra Chlorophyll production or more efficient methods of photosynthesis (C₄ Photsynthesis). (speculative)
Stimulates root senescence (speculative)
Directly or indirectly induces CK at high levels (speculative)
Inhibits the rate of metabolism of cells in the roots so as to funnel resources to the shoot for better acquisition of sugar and gases. (speculative)
Is a general indication of poor shoot health. May be released when the plant or plant part does not have enough shoot derived nutrients (sugar and gases) to continue existing at the present size, let alone growing. Action in general may be to increase sugar and gases, by either releasing stores, lowering root metabolism or inducing less needed root senescence. (speculative)
May work with Brassinosteroid to produce its effects. (speculative)