Abscisic acid treatment results in

The correct option is stomatal closure.

Explanation:
Abscisic acid (ABA) is a vital plant hormone (phytohormone) that primarily functions as a growth inhibitor and plays a crucial role in mediating plant responses to environmental stresses, particularly drought and water scarcity. Because of this, it is commonly referred to as the "stress hormone."

When a plant experiences water stress or drought, its roots detect the lack of moisture and synthesize abscisic acid, which is then transported to the leaves through the vascular system.

Once ABA reaches the guard cells surrounding the stomatal pores, it triggers a signaling cascade:
1. ABA binds to specific receptors on the guard cell membrane.
2. This binding stimulates the efflux (outward movement) of potassium ions ($K^{+}$) and other anions (like chloride ions, ${\mathrm{Cl}}^{-}$) from the guard cells.
3. The loss of these solutes increases the water potential inside the guard cells relative to the surrounding epidermal cells.
4. Consequently, water moves out of the guard cells by osmosis.
5. As water leaves, the guard cells lose their turgidity (become flaccid), causing them to collapse inward and close the stomatal pore.

By promoting stomatal closure, abscisic acid prevents excessive water loss through transpiration, helping the plant conserve water and survive during dry conditions.