Stomata would open when the two guard cells increases. Increased guard cell turgor pressure caused by the entry of water into the guard cells. Water movement from one cell to another will always be from cells that have a higher water potential to the cells to the lower water potential. High or low water potential of cells will depend on the amount of dissolved material (SoluTe) in the liquid cell. The more material dissolved the cell osmotic potential would decrease. Thus, if the cell turgor pressure is fixed, the overall water potential of cells will decline. To spur to prevent water entry into guard cells, the amount of material dissolved in the cell should be raised (Lakitan, 1993).
Stomatal activity occurs because the water relations of cells of the cover and helper cells. When the cells become turgid cover the thin cell walls bulge and thick cell wall surrounding the aperture (not bulging big enough) to be very hollow, thereby opening the aperture. Therefore, opening and closing of stomata depends on the changes of the cells turgiditas cover, ie if the cells turgid cover the hole open and cells loosened pore / hole cover (Pandey and Sinha, 1983).
At the time of stomatal opening would occur accumulation of potassium ions (K +) in guard cells. Potassium ion is derived from neighboring cells. Light plays an important role to stimulate the entry of potassium ions into guard cells and, if plants are placed in the dark, then potassium ions will be back out the guard cells (Lakitan, 1993).
When potassium ions into guard cells, the same number of hydrogen ions out, in which hydrogen ions are derived from organic acids are synthesized into the guard cells as a possible factor causing the opening of stomata. Generally, organic acids are synthesized malic acid which hydrogen ions contained therein. Malic acid is the most common result was found in normal circumstances. Because hydrogen ions derived from organic acids, the pH in guard cells will drop (it will become more acidic), if H + K + is not exchanged with the incoming (Salisbury and Ross, 1995).
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