Question

Explain stomatal opening and closing mechanism with reference to starch sugar interconversion theory.

Answer 1

According to the starch-sugar interconversion theory (Steward 1964), during the daytime, the enzyme phosphorylase converts starch to sugar, thus increasing the osmotic potential of guard cells and closing the entry of water, and thereby the guard cells are stretched, and the stoma widens. The reverse reaction occurs at night, bringing about the closure of the stoma.

\[\ce{\underset{(Stoma closes)}{Starch} <=>[Phosphorylase (Day)][Night] \underset{(Stoma opens)}{Sugar}}\]