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The Gibberellins


The early history of the gibberellins was an exclusive product of the Japanese scientists. In 1926, E.Kurosawa was studying a rice disease (Oryza sativa) called "mad plant disease", in which the plant grew rapidly, was tall, pale and sickly in color, with a tendency to fall.

Kurosawa discovered that the cause of such disease was a substance produced by a fungus species, Gibberella fujikuroi, which parasitized the seedlings.
Gibberellin was thus named and isolated in 1934. Gibberellins are possibly present in all plants, throughout their parts and in different concentrations, with the highest concentrations still in immature seeds. More than 78 gibberellins have been isolated and chemically identified. The best studied group is GA3 (known as gibberellic acid), which is also produced by the fungus Gibberella fujikuroi.

Gibberellins have drastic effects on the elongation of intact plant stems and leaves by stimulating both cell division and cell elongation.

Places of production of gibberellins in the vegetable

Gibberellins are produced in young kaolin system tissues and developing seeds. It is uncertain if its synthesis also occurs in the roots. After synthesis, gibberellins are probably transported by xylem and phloem.

Gibberellins and the Dwarf Mutants

Applying gibberellin to dwarf plants, they are found to be indistinguishable from plants of normal height (non-mutant plants), indicating that dwarf plants (mutants) are unable to synthesize gibberellins and that tissue growth requires this regulator.

Gibberellins and the seeds

In many plant species, including lettuce, tobacco, and wild oats, gibberellins break seed dormancy, promoting embryo growth and seedling emergence. Specifically, gibberellins stimulate cell elongation, causing the root to rupture the seed coat.

Practical applications of gibberellins

  1. Gibberellins can be used to break seed dormancy of various plant species, accelerating uniform crop germination. In barley seeds and other grasses, the gibberellin produced by the embryo accelerates digestion in nutrient reserves contained in the endosperm (reserve rich region) as it stimulates the production of hydrolytic enzymes.
  2. Gibberellins can be used to anticipate seed production in biennial plants. Together with cytokines, they play an important role in the seed germination process.
  3. Gibberellins, as well as auxins, can cause the development of (seedless) parthenocarpic fruits, including apple, pumpkin, eggplant and gooseberry. The largest commercial application of gibberellins is in the production of table grapes. Gibberellic acid promotes the production of large, seedless fruits, loose among themselves.
  4. Gibberellins stimulate flowering of long-day (PDL) and biennial plants.

In the farming

  1. Synthetic aids and gibberellins: Sprayed on crops, these substances cause simultaneous flowering of pineapple plantations, prevent the premature fall of oranges and allow the formation of seedless grapes. They also increase the storage time of potatoes, preventing their buds from sprouting.
  2. Experiments for the production of plant tissue culture with auxins and cytokines in nutrient solutions containing minerals, sugar, vitamins and amino acids. From this, large tissue masses (corns) of apple, pear, carrot, potato and others are produced. With these calli, new plants, selected and free of parasites can be obtained. Classical experiments carried out in 1950 were made to obtain clones (genetically iqual plants obtained from single vegetable somatic cells) from carrots by tissue culture.
  3. Use of plant hormones as selective herbicides: Some of them, such as 2,4-D (dichlorophenoxyacetic acid, a synthetic auxin) are harmless to grasses such as rice, wheat, rye, but kill broadleaf weeds such as ticks, prickles. , Dandelions.

For other purposes

  1. Some synthetic hormones can be toxic to animals and humans; Their indiscriminate use can trigger harmful side effects on communities and ecosystems. And another synthetic auxin, 2,4,5-T (trichloro-phenoxyacetic acid), used as a defoliation agent in the Vietnam War. This substance has been shown to be responsible for deformations in mammalian embryos. The dangerous effects of the substance result from its contamination by traces of benzodioxine, substance that forms during the manufacture of the hormone. Recent research shows that only five parts per trillion dioxin can significantly increase the likelihood of cancers of various types.