Gibberelin on flowering
Gibberelin
on flowering
Flowering is a cascade reaction consisting of several steps.Flowering
signal is first received by phytochrome in the leaf and transmitted from the
leaf to shoot apex.Upon arrival of the flowering stimulus, the growth mode of
the meristem is changed from vegetative to reproductive. The shoot apical
meristem produces primordia of floral organs; sepals, petals, stamens and
carpels.Among
the naturally occurring growth hormones, Gibberelins can have a strong
influence on flowering.It has been experimentally proved that gibberellin can substitute for the longday or cold
requirement for flowering in many plants.
Reknowned plant physiologist
Lang(1960) first demonstrate that added gibberelin could substitute for the
poper environmental condition in Hyocyamus
niger,which usually require a long day for flowering.The flower-inducing
activity of exogenously applied gibberellins is also clear in rosette-forming
long-day plants such as carrot. From these facts, gibberellins have been
considered as the precursor of flowering hormone, florigen. However this
conclusion was not accepted because gibberellins do not induce flowering in
short-day plants.The supporter researcher also conclude in favour of gibberelin
that, there is no reason to assume that florigen must be the same in different
plant species. Whether gibberellins are florigen or not should be examined from
the view point of whether endogenous gibberellins were actually involved in the
mechanism regulating flowering in one fixed plant species or not.
.
Endogenous levels of gibberellins have been compared between
flowering and vegetative plants of spinach, a long-day plant. The gibberellin
level increased under long-day conditions. However, inhibitors of gibberellin
synthesis did not inhibit flower formation although they inhibited stem
elongation. It was concluded that gibberellin was not involved in the flowering
of spinach.The role of gibberellins in flowering of short-day plants has been
well studied in Pharbitis nil. Endogenous gibberellin contents increase
under short-day conditions, inhibitors of gibberellin biosynthesis inhibit
flowering and this inhibition is nullified by gibberellin. However, application
of gibberellins did not induce flowering under long-day conditions. The process
promoted by gibberellin was found to be flower evocation. Therefore,
gibberellin is a factor promoting the action of florigen.
For studies
of genetic regulation of gibberellins on Aabidopsis also reveals the poper role
of gibberelin in floweing.In this study it was found that gibberellin similar
substance induce the production of florigen.In turn florigen activates LEAFY
gene. Activation of this gene regulate floral homeotic genes and controls the
formation of sepal , petal, stamen and carpel.
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