What is GA3 ?

GROWTH REGULATORS/STIMULATORS

They are plant hormones with regulating role in plant growth. They are natural products but they can also be synthesized, they are found in all plants and, if properly applied, they can make real "miracles". Based on these substances, are made simple or complex formulas that can speed up the formation of roots or stimulate the growth of leaves or fruit. The existence of the plant hormones has been suspected since the beginning of the last century. Numerous scientific papers on these topics have proved their presence, but they were able to identify only much later. The first plant hormones discovered were part of the auxin class, around the year 1934, gibberellins and cytokinins being discovered later, in the 1950s. These three types of growth regulators would exert a stimulating action on the cellular metabolism. There are substances which have inhibitory effects on the growth and development of plant cells such as abscisic acid, identified in 1965, and phenolic substances, identified several years later. These substances are endogenous, meaning that they are synthesized by plants. There are also artificial growth plant regulators with chemical formulas similar to the natural ones, featuring a similar physiological action.All of these substances, natural or synthetic, are called growth regulators and have certain common features:

  • they have effect in very low concentration, in high concentration they being toxic, that is why some of them are used as herbicides;
  • they have effect only by interacting with other plant regulators, their function being determined by the hormone balance established between them;
  • they interfere with a number of physiological phenomena which imply multiple modes of action so that the notion of hormone has been abandoned.

A substantial difference between artificial and natural growth plant regulators consists in the fact that natural ones can be controlled by cells' metabolic mechanisms, they being eliminated fast enough, while artificial ones linger much longer, they often being preferred for practical applications.

Growth regulators are classified in three large groups: gibberellins, auxins and cytokinins.

GIBBERELLINS

The effect of gibberellins was highlighted before their actual identification. Gibberellin was discovered by the Japanese who would study the length of rice plant. In 1898, Hotoaro Hori found that excessively lengthy plants had been exposed to the Gibberella fujikuroi fungus. The aqueous extract of fungus caused similar symptoms to the tested plants, thus leading to the idea of the existence of a substance responsible for these effects. Eiichi Kurosawa manages to chemically isolate gibberellic acid in 1926. Teijiro Yabuta isolates a non-crystalline form of acid in 1935, and eventually the crystalline compound was isolated in 1938 by Yabuta and Sumiki Yusuke.

Separation of gibberellins in pure state was very difficult due to the high molecular weights they had. The first gibberellin identified was gibberellic acid or GA3 (a complex called "gibberellin A"). This first discovery was followed by the discovery of other gibberellins until a total of approximately fifty gibberellins were identified in plants and fungi. They are all endogenous compounds. In practice, the gibberellins used are purified extracts. The most frequently used gibberellin is GA3 and the least used gibberellin is the GA4+GA7 or GA7 composite. Synthetic gibberellins were obtained in the 1980s. Gibberellins are active, stimulating substances, mainly present in seeds, tubers and roots. They stimulate seed germination, thus hastening the emergence of plantlets in the early stages of development. In mature plants, gibberellins lead to unusual growth of leaf surface and plant height. Applied in low concentrations, they can help obtain some mutant, giant plants. Another interesting effect is inducing of blooming, especially in biennial plants. Intense growth of plant's aerial part shall be induced by spraying the plants with minute amounts of solutions containing gibberellin. Root growth is hardly influenced or not at all affected. The treatment of cereals with gibberellin leads to a smaller ratio of dropping, due to the strengthening of the stem or shrinking the distance between nodes. Gibberellins cause gigantism both by accelerating cell multiplication and by increasing their size. Thus, dwarf corn develops up to the same height as the regular corn and fruits if treated with gibberellin. Seedless fruit, fast developing buds, fruit ripening can result by applying gibberellins. Yet, rapid development of plants treated with plant hormones is not possible without ensuring all the vegetation factors. Treatment with gibberellic acid has a considerable influence on the growth of grape clusters and berries. Researches of Weaver (1958), Weaver and Mc Cune(1959) have shown that treatment with gibberellin leads to a substantial elongation of grape clusters (from the cluster base to the tip of the main axis). The data show that the earlier treatment with gibberellin is applied (by 2-3 weeks before blossoming), the more elongated grape clusters become.

Features of gibberellins (GA)

  • they have effects on the elongation of in-between nodes areas, sometimes leading to spectacular results (e.g.: 3-m cabbage stem), but not on all species. Only some dwarf varieties can reach normal height following application of GA, usually dwarf varieties do not react to the elongating effect of the gibberellic acid.
  • they have effect upon flowering, by either inhibition of floral induction, such as in fruit trees, or by stimulating efflorescence of species that need low temperatures to bloom, so that, in the presence of gibberellins, these species can also bloom without low temperatures (carrot).

In other species, which also require low temperatures for efflorescence, the presence of gibberellins only induces stem elongation without formation of flowers (beets). These apparent contradictions have a simple explanation: cold acts only on the growth of the stem in the plants listed above in the first case, while cold has effects on the process of blooming in the second case. Thus, gibberellins only act as elongation stimulators, not affecting, in this case, the normal physiological processes;

  • they have effect on the formation of fruit in the case of pear trees, mandarin, plum trees;
  • they set off the effects of the yellow virus on cherries
  • they significantly improve flowering and productivity of strawberries
  • they lead to increasing number of blueberries per plant
  • they increase the size and quality of sweet cherries, the cherries being firmer and brighter
  • they increase productivity and quality of barley and hop for beer
  • they lead to a homogenous growth of rice seedlings
  • they interrupt hibernation and stimulate the germination of seed potatoes
  • they have a complex effect on seed germination or on the start of vegetation phases for dormant buds, when weather conditions (low temperatures) do not allow these, also inducing ramification or growth of branches;
  • elongation of central axis of grape clusters¬† and their lateral ramifications;
  • increasing the size of the grape berries;
  • increasing the average weight of grape clusters;
  • increase of productivity;
  • enlargement of seedless berries and the loss of flowers in some varieties with normal hermaphrodite flowers;
  • certain peculiarities are noticed in specific varieties, in terms of gibberellin's effects, concentration and application terms;
  • It shall NOT be used on cabbage as it makes it taste bitter and the cabbage becomes huge (cases of 3-m cabbage were reported) and the cabbage turns ligneous.