Question

Describe mechanism of opening and closing of stomata with reference to Starch-sugar interconversion theory.

Answer 1

Starch-sugar interconversion theory:

1. According to the starch-sugar interconversion theory (Steward, 1964), during the daytime, the enzyme phosphorylase converts starch to sugar, increasing the osmotic potential of guard cells.
2. This change allows the entry of water, causing the guard cells to stretch and the stoma to widen.
3. The reverse reaction occurs at night brining about the closure of stoma.
4. \[\ce{\underset{Stomata closes}{Starch}⇌[Phosphorylase(Day)][(Night)]\underset{Stomata opens}{Sugar}}\]