Usually relative turgor changes which maintain osmotic gradients in the guard cells cause stomatal movements. In many species the dominant participation of K+ in stomatal movements was well established. Organic acids such as malate, citrate, glutamate and aspertate were reported to serve as counter ions of K+ in many species. Both oxidative phosphorylation and photo phosphorylation are potential energy sources. In earlier studies, the functional role of PS II was not clearly understood. Hence

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... e present study is aimed to understand the role of PS II in guard cells of Dolicus biflorus Linn. a Fabaceae member. Influence of PS II electron acceptors and donors such as potassium ferricyanide, hydroxylamine hydrochloride, MnCl2, Sodium ascorbate, diphenyl carbazide, ATP, ADP, ATP + MnCl2 and ADP + MnCl2, MnCl2 + NADP and Hydroxylamine hydrochloride + NADP is studied to understand the role of photo system II on stomatal movements,