What is likely to happen when a plant is treated with defoliants?

When a plant is treated with defoliants, the primary effect is the activation of the abscission zone. Defoliants are chemicals that induce the shedding of leaves and can stimulate this natural process by promoting the breakdown of the cell layers in the abscission zone where the leaf stem attaches to the plant. This breaking down leads to leaf drop, which can be an important practice in agricultural settings, particularly for crops like cotton, where timely defoliation can aid in harvesting and improve fiber quality by allowing the plant to focus its resources on boll maturation instead of foliage.

The other options suggest effects that are not directly associated with defoliants. Enhanced growth and increased leaf size generally indicate a healthy, thriving plant, which is contrary to the purpose of applying a defoliant. Improved soil nutrients also do not relate to the function of defoliants, as these chemicals specifically target leaves rather than altering soil composition or nutrient levels. Thus, focusing on the activation of the abscission zone clearly aligns with the intended outcome of using defoliants on plants.