Which plant growth regulator is widely recognized as a stress hormone because it stimulates the closure of stomata and increases plant tolerance to various environmental stresses?

Step-by-step solution

Abscisic acid (ABA) plays an important role in plant responses to environmental stress. It stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone. Ethylene is a gaseous hormone involved in fruit ripening and senescence. Indole butyric acid is a synthetic auxin used to initiate rooting. Kinetin is a cytokinin that promotes cell division. Answer: Abscisic acid