AP BIOLOGY

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: -Abscisic acid (ABA) is a plant hormone involved in the response of plants to reduced water availability. Reduction of guard cell turgor by ABA diminishes the aperture of the stomatal pore and thereby contributes to the ability of the plant to conserve water during periods of drought.

Detailed explanation-3: -Abscisic acid-induced stomatal closure is mediated by ion efflux from guard cells. Ion efflux in turn leads to osmotic water efflux and a reduction in the turgor and volume of the guard cells, resulting in stomatal closure.

Detailed explanation-4: -Abscisic acid (ABA) is an important phytohormone regulating plant growth, development, and stress responses.

Detailed explanation-5: -Among these, abscisic acid (ABA), is the best-known stress hormone that closes the stomata, although other phytohormones, such as jasmonic acid, brassinosteroids, cytokinins, or ethylene are also involved in the stomatal response to stresses.