What Are Gibberellins?

What are Gibberellins- plant hormones that stimulate growth in the stem and leaves, trigger the germination of the seed and breaking of bud dormancy.

There are five major classes of plant hormones auxin, cytokinins, gibberellins, abscisic acid and ethylene. Generally theses plant hormones control the plant growth and the development by affecting the division, elongation and differentiation of the cells. In some cases the hormones are also able to mediate shorter-term physiological responses plants to environments stimuli. Each hormone has a multiplicity of effects. The effects have directly are related to their site where there action takes place, the developmental stage the plant is in and the concentration of the hormone. The plant hormones are produce in very small amounts yet this small amount can have a profound effect on the growth and the development of the plant organ.

Gibberellins are defined as a class of related plant hormones that stimulate growth in the stem and leaves, trigger the germination of the seed and breaking of bud dormancy, and stimulate fruit development with auxin.

In 1926 E Kurosawa discovered that the reason seedlings where growing so tall and toppling over is because of the disease caused by a fungus of the genus Giberella. Four years later Japanese scientist concluded that the fungus produced hyperelongation of stems by secreting a chemical called gibberellins. The western scientist learned of gibberellins after World War II. Over the last thirty years many different scientist identify over seventy types of gibberellins, most of which occurred naturally in plants. Some types are much more active then others. Growth regulators are normally overdosed in plants of lower concentrations. Gibberellins have many different effects on plants.



Gibberellins production occurs mainly in the roots and young leaves. Little growth actually occurs in the root but mainly in the leaves and stems. Even though there is little effect on the root growth, the gibberellins stimulate growth in the stems and leaves. Inside the stems the gibberellins stimulate cell division and cell elongation. Both auxin and gibberellins have to act together in a growing stem. Gibberellins generally have no influence on plants of normal size. Yet if a dwarf plant has gibberellins added to it, then it can grow to normal size.

In the development of fruit there is also dual control by auxin and gibberellins. There are fruits that require both hormones to be set. The main time gibberellins spray is used, is on seedless grapes to make them grow further apart.

Most seeds have a high concentration of gibberellins in the embryo. Once water is imbibed, the gibberellins are released from the embryo it tells the seed to break the dormancy and germinate. Naturally gibberellins are the key part in renewing the growth of the embryo.

Ceral seedlings growth is supported by gibberellins that stimulate they synthesis of the digestive enzymes. Gibberellins stimulate the synthesis of messenger RNA coding for amylase, before the enzymes even appear. The gibberellins also work to break dormancy when growth of apical buds start growing again. Abscisic acid, another hormone that usually inhibits plant growth, works against gibberellins in both the growth of the bud and seed dormancy.

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