Class 11 NEET Biology Plant Growth and Development

(a) : Absisic acid is a hormone 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. Abscisic acid inhibits the K+ uptake by guard cells and promotes the leakage of malic acid. It results in reduction of osmotically active solutes so that the guard cells become flaccid and stomata get closed.