When plants are under severe water shortage, which hormone is known to close the stomata?

Abscisic Acid is crucial in regulating water loss in plants, particularly during periods of severe drought or water shortage. This hormone triggers the closure of stomata, which are the tiny openings on the surfaces of leaves that facilitate gas exchange. When water levels are low, the production of Abscisic Acid increases, signaling the guard cells surrounding the stomata to close. This closing action helps to reduce transpiration, minimizing water loss and conserving moisture within the plant.

While ethylene is primarily involved in processes like fruit ripening and stress responses, cytokinins promote cell division and growth, and gibberellins are associated with stem elongation and seed germination, they do not play a direct role in stomatal closure during water stress. Therefore, Abscisic Acid is the key hormone in this context, effectively helping plants manage their water resources.