BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Abscisic acid (ABA) is a stress hormone that accumulates under different abiotic and biotic stresses. A typical effect of ABA on leaves is to reduce transpirational water loss by closing stomata and parallelly defend against microbes by restricting their entry through stomatal pores.

Detailed explanation-2: -Cytokinins (CK) and auxins (AUX) in low physiological concentrations promote stomatal opening while in high concentrations, they are able to inhibit this process. The role of ethylene (ET) is the most curious. It can stimulate the closing and opening of the stomata.

Detailed explanation-3: -Abstract. Previous studies have shown that cytokinins and auxins can induce the opening of stomata.

Detailed explanation-4: -ABA is a key hormone that regulates water status and stomatal movement. Under drought conditions, plants produce and accumulate increased amounts of ABA in the guard cells, and this induces stomatal closure to conserve water.