AP BIOLOGY

Detailed explanation-1: -Excess loss of water through the stoma, such as during a drought, triggers chemical reactions that signal water and ions to leave the guard cells. As solutes exit the guard cells, the pair “deflates, ” subsequently closing the stoma like two flat balloons.

Detailed explanation-2: -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. ABA can also promote the accumulation of polyamines, sphingolipids, and even proline.

Detailed explanation-3: -In guard cells, the plant hormone abscisic acid (ABA) inhibits stomatal opening and induces stomatal closure through the coordinated regulation of ion transport. Despite this central role of ABA in regulating stomatal function, the signal transduction events leading to altered ion fluxes remain incompletely understood.

Detailed explanation-4: -Plants lose water primarily by gaseous exchange through the stomata on their leaves. 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.