Page 262 - Biology_F5

Coordination and Irritability

used in removing dicotyledonous weeds in Application of synthetic gibberellins in
cereal (monocotyledonus) crops. Benzoic crop production
acids are also used as a powerful weed The synthetic gibberellins have the following
killer, thus they are used against deep- roles in plants:
rooted weeds. (a) They promote fruit setting.
(b) They enhance malting in brewing
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(d) Prevent sprouting in potatoes industries.
Phenoxyacetic acid is used to prevent (c) They reverse genetic dwarfism.
sprouting in potatoes. It is also used to (d) They break seed dormancy.
prevent premature falling of fruits and
leaves in crop plants. (e) They increase plants’ resistance to pests
and diseases.

Gibberellins
Gibberellins, such as Gibberellic Acid Cytokinins
(GA) include a wide range of chemicals Cytokinins (CKs) are a group of chemicals
that are produced naturally within plants. that influence cell division and shoot
Like auxins, which can be produced in formation in plants. In the past, when the
industry, gibberellins are also commercially cytokinins were first isolated from yeast
produced from fungal culture. They cells they were called ‘kinins’. They are
perform the following role in plants: found mostly in regions of rapid cell
(a) They stimulate stem elongation and division, particularly in seeds and fruits,
where embryos develop. They perform the
pollen tube growth. following roles in plants:

(b) They influence cell division. (a) They promote cell division in the
(c) They promote flowering, seed germination presence of auxins.
and differentiation after germination. (b) They induce delayed senescence of
(d) They are important for seed germination, leaves and fruits.
as they effect enzyme production that (c) They are responsible for mediating
mobilises food production needed for transportation of auxins throughout the
growing new cells. This is done by plant and affecting internodal length and
modulating chromosomal transcription growth.
in the growing seedling. (d) They promote lateral bud growth.

(e) They promote bolting in rosette plants, (e) They counteract the apical dominance
hence increasing inter nodal lengths. induced by auxins.
(f) They promote cell division and (f) They break seed and bud dormancy at
elongation in the presence of auxins. appropriate temperatures.
(g) They reverse the inhibition of shoot Application of synthetic cytokinins in
growth and dormancy induced by crop production
Abscisic acid. Synthetic cytokinins have the following

(h) They break seed dormancy. application in crop production:

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