Starch breaks down, producing sucrose and malate. These, along with the influx of ions, increases the solute concentration inside of the guard cells, driving water into the cells., The stomata open and close in response to changes in light levels and temperature. This allows them to absorb carbon dioxide from the air during photosynthesis and release oxygen back into our environment., Starch metabolism in guard cells plays a central role in regulating stomatal movement in response to light, elevated ambient CO 2 and potentially other abiotic and biotic factors., Transitory starch in these cells plays a key role in determining the velocity of stomatal opening in the light. This significantly differs from the transitory starch in the mesophyll leaves, which acts primarily as a carbohydrate reserve to sustain plant metabolism during the night., Stomata open at the leaf epidermis, driven by solute accumulation in the surrounding guard cells. Transmembrane ion transport has long been recognised to contribute to this process. A new study makes it clear that guard cells also metabolise starch to accelerate opening., Starch-Sugar Interconversion: The stomata normally open during day and close during night. Actually, during daytime at pH7, the starch is converted to glucose 1 phosphate, which is soluble in water, so the osmotic potential of the guard cell increases, endosmosis occurs and the guard cell opens. during night time, the pH is reduced to 5,.