Class 11 NEET Biology Plant Growth and Development

(d) : Abscisic acid is a hormone which is produced during adverse environmental condition. It also causes the closure of stomata under conditions of water stress as also under high concentration of CO2 in the guard cells. ABA plays an important role in plants during water stress and drought conditions.The concentration of ABA increases in the leaves of plants facing such stresses, hence it is called as a stress hormone.