The second type of antitranspirants are metabolic inhibitors. The most common being (ABA) Abscisic acid. ABA is also called Abscisin originally found to induce abscission, and Dormin originally found to induce dormancy. ABA is a naturally occurring plant hormone that plays several roles in regulating various stages of plant growth. ABA is also produced in response to plant stresses and induces the production of plant proteins that are associated with acclimating plants to plant stresses. When plants experience water stress due to dry soil conditions the roots synthesize ABA and send chemical stress signals to the leaves. Changes take place in the leaves in response to these stress signals effecting the osmotic potential of the guard cells that surround the stomata. This causes the stomata to close reducing the amount of water lost through transpiration so the plant is able to retain as much water as possible for survival.

This naturally occurring plant hormone has been synthetically reproduced resulting in a man made (PGR) plant growth regulator. While this type of antitranspirant can be applied as a foliar spray it does not form a protective plant coating like the antitranspirants mentioned in Type 1. While this type has primarily been used as a foliar spray it can be applied as a soil drench to be taken up by the roots. The downsides to using ABA as an antitranspirant include but are not limited to it’s overall cost and the duration of it’s effectiveness, usually a matter of days. In contrast the film forming antitranspirants like Nature Shield™ form a protective plant coating over the leaves and plant surfaces that reduce water loss through the stomata, cuticles, stems and other plant tissues that can last for weeks or months. The film forming antitranspirants are also less expensive.