Spraying Dwarf Plants With Gibberelin

Gibberellin Aj (important in stem growth)

Gibberellin A3 (commercially available)

In 1809, the study of the gibberellins began indirectly with observations of the bakanae, or "foolish seedling," disease of rice. Seedlings affected by this disease grow tall more rapidly than their healthy neighbors, but this rapid growth gives rise to spindly plants that die before producing seeds (the rice grains used for food). The disease has had considerable economic impacts in several parts of the world. It is caused by the ascomycete fungus Gibberella fujikuroi.

In 1925, the Japanese biologist Eiichi Kurosawa grew G. fujikuroi on a liquid medium, then separated the fungus from the medium by filtration. He heated the filtered medium to kill any remaining fungus, but found that the resulting heat-treated filtrate was still capable of inducing rapid growth in rice seedlings. Medium that had never contained the fungus did not have this effect. This experiment established that G. fujikuroi produces a growth-promoting chemical substance, which Kurosawa called a gibberellin.

Were the gibberellins simply exotic products of an obscure fungus, or did they play a more general role in plant growth? Bernard O. Phinney of the University of California, Los Angeles, answered this question in part in 1956, when he reported the spectacular growth-promoting effect of gib-berellins on dwarf corn seedlings. He used plants that were known to be genetic dwarfs, in which a particular recessive allele (say, d1) was present in the homozygous condition (dldl). Gibberellins applied to nondwarf—wild-type—corn seedlings had almost no effect, whereas dwarf seedlings treated with gibberellins grew as tall as their normal relatives. (A comparable effect of gibberellins applied to a dwarf tomato plant is shown in Figure 38.5.)

22 days after being sprayed with a dilute gibberellin solution, this plant reached the size of a nondwarf plant.

22 days after being sprayed with a dilute gibberellin solution, this plant reached the size of a nondwarf plant.

Plants Without Gibberellins
38.5 The Effect of Gibberellins on Dwarf Plants Both of the dwarf tomato plants in this photograph were the same size when the one on the right was treated with gibberellins.

Phinney drew two conclusions from the results of this experiment: first, that gibberellins are normal constituents of corn, and perhaps of all plants, and second, that some dwarf plants are short because they produce insufficient amounts of gibberellins. According to Phinney's hypothesis, nondwarf plants manufacture enough gibberellins to promote their full growth, but dwarf plants do not. Extracts from numerous plant species were found to promote growth in dwarf corn. These findings provided direct evidence that plants that are not genetic dwarfs contain gibberellin-like substances. Phin-ney's work set the stage for today's use of mutant plants to investigate the control of plant development.

The roots, leaves, and flowers of dwarf corn plants appear normal, but their stems are much shorter than those of wildtype plants. All parts of the dwarf plant contain a much lower concentration of gibberellins than do the organs of a wild-type plant. We can infer, then, that normal stem elongation requires gibberellins or the products of gibberellin action. We can further infer that gibberellins play a less essential role in the development of roots, leaves, and flowers.

Although more than 125 gibberellins have been identified, only one, gibberellin A:, actually controls stem elongation in most plants. The other gibberellins found in stems are simply intermediates in the production of gibberellin Ar As we will see in the next section, gibberellins affect processes other than stem elongation, but we do not yet know which gib-berellin has any other particular effect.

38.6 Bolting Spraying with gibberellins causes cabbage and some other plants to bolt.

The internodes of plants treated with gibberellin elongate dramatically, resulting in towering shoots.

Untreated control plants retain their compact, leafy heads.

Untreated control plants retain their compact, leafy heads.

Cabbage Stem Elongation
Without gibberellin

With gibberellin

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Responses

  • leah
    How gibberellins work in plants?
    8 years ago
  • Susanna
    What happens when cabbage is treated with gibberellins?
    3 years ago
  • Duane
    What hapoens when cabbag3 is treated in Gibberelins?
    2 years ago
  • chilimanzar
    What happens when cabbage is treated with gibberelins?
    2 years ago
  • thea
    What happens when cabbage is treated with gibberelin?
    2 years ago
  • gemma
    Why dwarf plants look tall when treated with gibberellin?
    2 years ago

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