Plant growth regulator//functions of gibberellin

Plant hormones, also known as phytohormones, are
chemicals that regulate plant cell processes. They are
signal molecules produced within the plant functioning in
extremely low concentrations
Five major types of plant hormones
1. Auxin
2. Gibberellin
3. Cytokinin
4. Ethylene
5. Abscisic acid
Plant growth regulators usually are defined as organic
compounds, other than nutrients, that in small
Concentrations, affect the physiological processes of
plants"

2. Gibberellins
Gibberellins are synthesized in young tissues of the
shoots, uncertainly in roots and also in the developing
seeds. There are also some evidences that leaves may be
the source of some biosynthesis
Discovery of Gibberellins
A Japanese scientist E. Kurosawa in 1926 found that some
of the rice seedlings grow taller than others. He
discovered the seedlings to be infected by the pathogenic
fungus Gibberella fujikuroi. In 1935, an agricultural chemist
T. Yabuta isolated a non-crystalline material from the
similar type of culture that he named as "gibberellins"
gibberellins are derived from the gibberellane skeleton.
The gibberellins are named GA1, GA2, GA3, .., GAn in their
order of discovery. Gibberellic acid -GA3, was first
structurally characterised gibberellin. There are at present
136 GAs that have been identified from plants, fungi and bacteri.
Functions of Gibberellins
Physiological processes stimulated by active gibberellins
depend on their types.
1-Stimulate cell elongation in stem
2-Breaks seed dormancy in some plants which requires
light for germination
3-Stimulates alpha-amylase production in germinating
cereal grains
4-Stimulates bolting/fl owering in response to long days
5-Delay senescence in leaves and also in citrus fruits
6-Induces maleness in dioecious flowers
7-Play a role in development of seedless fruit
(parthenocarpic).
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