Please explain the sugar concentration theory of opening and closing of stomata.... In detail

Dear Student, Sugar Concentration theory is one of the oldest theories. According to this theory, during daytime gaurd cells of the leaf perform photosynthesis to produce sugar. This sugar present in cells increase osmotic pressure due to which endosmosis takes place and gaurd cells swells up to open stomata. During night, when there is shortage of water in roots, loss of water from gaurd cells takes place and gaurd cells shrink to close the stomata. Hope it helps you! Regards.