that upon phosphorylation, a 14-3-3 protein was bound to the phototropins before the H+-ATPase had been phosphorylated. In a similar experiment they concluded that the binding of 14-3-3 protein to the phosphorylation site is essential for the activation of plasma membrane H+-ATPase activity. This was done by adding phosphopeptides such as P-950, which inhibits the binding of 14-3-3 protein, to phosphorylated H+-ATPase and observing the amino acid sequence. As protons are being pumped out, a negative electrical potential was formed across the plasma membrane. This hyperpolarization of the membrane allowed the accumulation of charged potassium (K+) ions and chloride (Cl−) ions, which in turn, increases the solute concentration causing the water potential to decrease. The negative water potential allows for osmosis to occur in the guard cell, so that water enters, allowing the cell to become turgid. Opening and closure of the stomatal pore is mediated by changes in the turgor pressure of the two guard cells. The turgor pressure of guard cells is controlled by movements of large quantities of ions and sugars into and out of the guard cells. Guard cells have cell walls of varying thickness(its inner region, adjacent to the stomatal pore is thicker and highly cutinized) and differently oriented cellulose microfibers, causing them to bend outward when they are turgid, which in turn, causes stomata to open. Stomata close when there is an osmotic loss of water, occurring from the loss of K+ to neighboring cells, mainly potassium (K+) ions Water loss and water use efficiency Water stress (drought and salt stress) is one of the major environmental problems causing severe losses in agriculture and in nature. Drought tolerance of plants is mediated by several mechanisms that work together, including stabilizing and protecting the plant from damage caused by desiccation and also controlling how much water plants lose through the stomatal pores during drought. A plant hormone, abscisic acid (ABA), is produced in response to drought. A major type of ABA receptor has been identified. The plant hormone ABA causes the stomatal pores to close in response to drought, which reduces plant water loss via transpiration to the atmosphere and allows plants to avoid or slow down water loss during droughts. The use of drought-tolerant crop plants would lead to a reduction in crop losses during droughts. Since guard cells control water loss of plants, the investigation on how stomatal opening and closure is regulated