Potassium also regulates the plant’s efficient use of water and can help protect the plant against environmental stress. If there is plenty of potassium and other solutes in root cells, water is drawn into the roots for uptake by the plant. Potassium also regulates the opening and closing of stomata in the leaf cells. Stomata are the pores in the leaves that take in carbon dioxide from the air and release water vapor and oxygen. When adequate water and light are available, potassium is pumped into the guard cells of the stomata. The potassium draws water into the guard cells, causing them to swell and open. But if there is a water shortage, potassium is pumped out of the guard cells and the stomata close, helping the plant conserve water. With adequate potassium the opening/closing response is very fast, taking just a few minutes. But with inadequate potassium, the response is sluggish, often taking hours! The plants begin to suffer from water stress, and photosynthesis begins to shut down. Even if the symptoms of potassium deficiency are not obvious, the plants may suffer from “hidden hunger”, reducing overall quality and yield.