what is gibberellic acid (GA-3) used for?

Your questions about GA are quite complex

I recommend that you go to the extensive information at
the Plant Hormones web site:

http://www.plant-hormones.bbsrc.ac.uk/
and
http://www.lars.bbsrc.ac.uk/plantsci/gas.html

The following information is copied from the later page

And if you are reallllly interested search their mail archive!

regards
Joel Kroin

--------------------------

Gibberellins (GAs) are a group of diterpenoid acids that function as plant
growth regulators inflencing a range of developmental processes in higher
plants including stem elongation, germination, dormancy, flowering, sex
expression, enzyme induction and leaf and fruit senescence. The origin of
research into gibberellins can be traced to Japanese plant pathologists who
were investigating the causes of the "bakanae" (foolish seedling) disease
which seriously lowered the yield of rice crops in Japan, Taiwan and
throughout the Asian continent.
Symptoms of the disease are pale yellow, elongated seedlings with slender
leaves and stunted roots. Severely diseased plants die whereas plants with
slight symptoms survive but produce poorly developed grain, or none at all.

Bakanae is now easily prevented by treatment of seeds with fungicides prior
to sowing. The first paper on the cause of bakanae was published in 1898 by
Shotaro Hori who demonstrated that the symptoms were induced by infection
with a fungus belonging to the genus Fusarium, probably Fusarium
heterosporium Nees.



Characteristic elongated rice seedling caused by bakanae

In 1912, Sawada published a paper in the Formosan Agricultural Review
entitled "The Diseases of Crops in Taiwan" in which he suggested that the
elongation in rice seedlings infected with bakanae fungus might be due to a
stimulus derived from fungal hyphae.

Subsequently, Eiichi Kurosawa (1926) found that culture filtrates from dried
rice seedlings caused marked elongation in rice and other sub-tropical
grasses. He concluded that bakanae fungus secretes a chemical that
stimulates shoot elongation, inhibits chlorophyll formation and suppresses
root growth.

Although there has been controversy among plant pathologists over the
nomenclature of bakanae fungus, in the 1930s, the imperfect stage of the
fungus was named Fusarium moniliforme (Sheldon) and the perfect stage,
Gibberella fujikuroi (Saw.) Wr. by H.W. Wollenweber. The terms "Fujikuroi"
and "Saw." in Gibberella fujikuroi (Saw.) Wr. were derived from the names of
two distinguished Japanese plant pathologists, Yosaburo Fujikuro and
Kenkichi Sawada.

Teijiro Yabuta initiated work on the isolation of the active component using
the fungal strains provided by Kurosawa. In 1934, Yabuta isolated a
crystalline compound from the fungal culture filtrate that inhibited growth
of rice seedlings at all concentrations tested. The structure of the
inhibitor was shown to be 5-n-butylpicolinic acid or fusaric acid. The
formation of fusaric acid in culture filtrates was suppressed by changing
the composition of the culture medium. As a result, a non-crystalline solid
was obtained from the culture filtrate that stimulated the growth of rice
seedlings. This compound was named gibberellin by Yabuta in 1935; the first
use of the term "gibberellin" in the scientific literature.

In 1938, Yabuta and his associate Yusuke Sumiki finally succeeded in
crystallizing a pale yellow solid to yield gibberellin A and gibberellin B
(The names were subsequently interchanged in 1941 and the original
gibberellin A was found to be inactive.) Determination of the structure of
the active gibberellin was hampered by a shortage of pure crystalline
sample. By current standards the productivity of their fungal strain was
extremely poor and they did not know that their sample of gibberellin A was
not pure, but a mixture of structurally-related gibberellins.

In the United States, the first research on gibberellins began after the
Second World War by a research unit at Camp Dietrick, Maryland. In 1950,
John E. Mitchell reported optimal fermentation procedures for the fungus, as
well as the effects of fungal extracts on the growth of bean (Vicia
faba)seedlings(Mitchell & Angel 1951). Work also began at the Northern USDA
Regional Research Laboratories in Peoria, Illinois in the USA using the
strain provided by Mitchell. Large scale fermentations were carried out with
the purpose of producing pure gibberellin A for agricultural uses but
initial fermentations were inactive.

In 1951, Sumiki visited the United States and met Frank H. Stodola. After
returning to Japan he sent new cultures to the USA but these also proved
inactive. The problem was traced to the lack of magnesium in the culture
medium and good yields of gibberellin were obtained when the culture medium
was supplemented with magnesium sulphate. The physical properties of
gibberellin isolated from these fermentations were found to be surprisingly
different from those reported by the Japanese and the new compound was named
gibberellin-x. (Stodola et al., 1955).

At about the same time in the UK, a team of researchers ( Philip Curtis,
Brian Cross, John Grove, Jake MacMillan and Paddy Mulholland) at Akers
Research Laboratories (ICI) isolated a new gibberellin which was given the
name "gibberellic acid".This compound had physical properties different from
the Japanese gibberellin A(Curtis & Cross, 1954). Samples were exchanged
between Stodola and Grove and "gibberellic acid" and gibberellin-X were
found to have identical chemical and physical properties and the name
gibberellic acid was accepted by both groups. A structure for gibberellic
acid was proposed in 1956 but later revised see Grove 1961.

In 1955, members of Sumuki group, (Takahashi et al.) succeeded in separating
the methyl ester of gibberellin A into three components, from which
corresponding free acids were obtained and named gibberellins A1, A2, and
A3. Gibberellin A3 was found to be identical to gibberellic acid. In 1957,
Takahashi et al. isolated a new gibberellin named gibberellin A4 as a minor
component from the culture filtrate.

In the mid 1950s, evidence that gibberellins were naturally occurring
substances in higher plants began to appear in the literature. Using
techniques that had been used to isolate gibberellins from the fungus,
Margaret Radley at ICI in the UK demonstrated the presence of
gibberellin-like substances in higher plants. In the USA, the first reports
of a gibberellin-like substance in maize came from Bernard Phinney et al
using dwarf maize mutants to assay for activity in plant extracts. This was
followed by the isolation of crystalline gibberellin A1, A5, A6 and A8 from
runner bean (Phaseolus multiflorus) (MacMillan et al. 1958, 1959,
1960,1962). The original samples from these isolations are now on display at
Long Ashton.

In the 1960s the number of gibberellins reported in the literature isolated
from fungal and plant origins rapidly increased. In 1968, J. MacMillan & N.
Takahashi reached an agreement that all gibberellins should be assigned
numbers as gibberellin A1-x, irrespective of their origin. Over the past 20
years using modern analytical techniques many more gibberellins have been
identified. At the present time the current number of gibberellins
identified is 94.

For a more detailed description of the history of gibberellins please see
Phinney, B.O.(1983) and Tamura, S. (1990)

Steve Croker (steve.croker@bbsrc.ac.uk)
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