application of gibberellin is called bolting (Figure . ). • Gibberellin breaks dormancy in potato tubers. • Many biennials usually flower during second year of their growth.
For flowering in the first year it self these plants should be treated with gibberellins. • Formation of seedless fruits without fertili- zation is induced by gibberellins Example: Seedless tomato, apple and cucumber. • Promotes elongation of inter-node in sugarcane without decreasing sugar content. • Promotion of flowering in long day plants even under short day conditions.
• It stimulates the seed germination. Figure . : Bolting (a) Untreated plant (b) Treated plant showing bolting. Rosette leaves .
. Cytokinins (Cytos – cell, Kinesis – division) . Discovery The presence of cell division inducing substances in plants was first demonstrated by Haberlandt in in Coconut milk (liquid gibberellin by Yabuta ( ). These are more than gibberellins reported from both fungi and higher plants.
They are noted as GA , GA , GA and so on. GA is the first discovered gibberellin. In , Yabuta and Sumiki isolated gibberellin in crystalline form. In1955, Brain et al., gave the name gibberellic acid .
In , Cross et al., established its structure. Agent Orange Mixture of two phenoxy herbicides , -D and , , -T is given the name ‘Agent orange’ which was used by USA in Vietnam war for defoliation of forest (chemical warfare). In botanical gardens and tea gardens, gardeners trim the plants regularly so that they remain bushy. Does this practice have any scientific explanation?
Yes, trimming of plants removes apical buds and hence apical dominance. The lateral buds sprout and make the plants bushy. . Occurrence The major site of gibberellin production in plants is parts like embryo, roots and young leaves near the tip.
Immature seeds are rich in gibberellins. . Precursors The gibberellins are chemically related to terpenoids (natural rubber, carotenoids and steroids) formed by -C precursor, an Isoprenoid unit called Iso Pentenyl Pyrophosphate (IPP) through a number of intermediates. The primary precursor is acetate.
. Chemical structure All gibberellins have gibbane ring structure. . Transport in plants The transport