Question: 125: The gaseous plant growth regulator is used in plants to :
(1) help overcome apical dominance
(2) kill dicotyledonous weeds in the fields
(3) speed up the malting process
(4) promote root growth and roothair formation to increase the absorption surface
Answer: Option (4)
Explanation:
Ethylene is the only gaseous plant growth regulator.
Ethylene promotes several physiological responses in plants,
including stimulation of root growth and enhancement of root hair formation.
Increased root hair development enlarges the absorption surface area,
improving water and mineral uptake by the plant.
Overcoming apical dominance and promoting lateral growth is mainly associated with cytokinins.
Selective killing of dicotyledonous weeds is carried out by synthetic auxins such as
2,4\text{-}D.
Malting involves the action of gibberellins, which stimulate the synthesis of
hydrolytic enzymes in germinating seeds.
Therefore, the correct use of the gaseous plant growth regulator corresponds to Option (4).