Stomatal opening in plants occurs due to influx of

It has been now experimentally proved that opening of stomata is an energy consuming process and not closing. The turgidity of guard cells is usually controalled by $\mathrm{K}^{+}, \mathrm{Cl}^{-}$and $\mathrm{H}^{+}$. The opening of stomata is initiated by excretion of $\mathrm{H}^{+}$by guard cells, intake of $\mathrm{K}^{+}$and $\mathrm{Cl}^{-}$and closing is controlled by abscisic acid.