Which of the following theory gives the latest explanation for the closure of stomata?
a)	ABA theory	b)	Munch theory
c)	Starch glucose theory	d)	Active transport theory

(a)

ABA theory to explain the mechanism of stomatal closure was proposed by Cowan et al, in 1982. According to it formation of abscisic acid (during drought or mid-day) promotes reversal of  pump and increases availability of  inside the guard cell cytoplasm and stomata close. Active  transport theory for opening and closing of a stomata, was proposed by Imamura (1943) and Fujino (1967). Proton  transport theory was proposed by Levitt (1974).