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A Handbook of Biology
There are more than 100 gibberellins (GA1, GA2, GA3 and so on) in fungi
and higher plants.
Gibberellic acid (GA3 or terpenes) is one of the first discovered and most
intensively studied gibberellins.
FÜÑÇTÏØÑS
They cause an increase in length of axis. So they are used to increase
the length of grapes stalks.
To elongate and improve the shape of fruits such as apple.
They delay senescence. So, the fruits can be left on the tree to extend
the market period.
GA3 is used to speed up malting process in brewing industry.
Sugarcane stores sugar in stems. Spraying sugarcane crop with
gibberellins increases the length of the stem. It increases the yield by as
much as 20 tonnes per acre.
Spraying juvenile conifers with GAs hastens the maturity period. It leads
to early seed production.
Promotes bolting (internode elongation just prior to flowering) in beet,
cabbages and many plants with rosette habit.
(AIPMT 2004)
3 CYTOKINInS
F. Skoog and co-workers observed that from the
internodal segments of tobacco stems the callus
(a mass of undifferentiated cells) proliferated only
if, in addition to auxins, the nutrients medium was
supplemented with extracts of vascular tissues, yeast
extract, coconut milk or DNA.
Skoog & Miller later identified and crystallised the cytokinesis promoting
active substance and termed as kinetin.
Cytokinins were discovered as kinetin (N6-furfurylaminopurine -an
adenine derivative) from the autoclaved herring sperm DNA.
Kinetin does not occur naturally in plants.
Zeatin (from corn-kernels and coconut milk) is the natural substances
with cytokinin-like activities.
There are some synthetic compounds with cell division promoting activity.
Natural cytokinins are synthesised in regions of rapid cell division (root
apices, shoot buds, young fruits etc).