In 1974 scientist Lavitt published the modern theory of stomatal opening and closing. Later Raschke, (1975), Noggle, Fritz (1976) and other scientists supported this theory. This is universally accepted doctrine.
Stomatal opening technique
(i) Blue (430-460nm) light enters the guard cell during the day. Under the influence of blue light, the white matter of the guard cells is converted into phosphoenol pyruvic acid.
(ii) phosphoenol pyruvic carboxylase enzyme reacts phosphoenol pyruvic acid and CO2 to produce oxaloacetic acid.
Oxaloacetic acid is converted to malic acid under the action of (Rorr) malic dehydrogenase enzyme.
(iii) Malic acid dissociates to form hydrogen ion (H+) and malate ion [R(COO-)2].
(iv) H+ moves from the guard cell into the accessory cell and K+ from the accessory cell into the guard cell.
(v) K+ reacts with malate ions in the guard cell to form potassium malate.
(vi) Potassium malate increases the osmotic pressure of the guard cell and water enters the guard cell in the process of endosmosis. This causes swelling of the guard cells and opening of the stomata.

stomatal closure technique
(i) K+ and malate ions are produced by breakdown of potassium malate in guard cells at night.
(ii) K+ moves from the guard cell into the accessory cell and H+ from the accessory cell into the guard cell.
(iii) reacts with hydrogen ion (H+) and malate ion [R(COO – )2] in the guard cell to form malic acid.
(iv) As K+ escapes from the guard cell, the osmotic pressure of the guard cell decreases and water escapes by the process of exudation.
(v) Guard cells lose water and become silent and stomata close.

In 1943, scientist Imammura first discovered the role of K+ in stomatal opening. In 1959, Japanese scientists Imammura & Fujino using radioactive isotopes proved that the opening and closing of stomata is regulated by the active absorption of K+ ions.
(i) Stomatal opening technique
During the day, guard cells absorb large amounts of K+ and Cl- ions. As a result, the osmotic pressure of the guard cell increases and water enters the guard cell in the process of endosmosis. At this time the turgor pressure (TP) of the guard cell increases and the guard cell bends like a bow. As a result, the pore opens.
(ii) Mechanism of stomatal closure
K+ and Cl- ions are released from the guard cell at night. As a result, the osmotic pressure of the guard cell decreases and water escapes from the guard cell in the process of exudation. At this time the turgor pressure (TP) of the guard cell decreases and the guard cell relaxes. As a result, the stomata are closed.

In 1964, scientist Steward introduced the theory of starch-glucose conversion.
(i) Stomatal opening technique
CO2 is used in the photosynthetic process in the guard cells during the day. This decreases the CO2 concentration in the guard cells and increases the pH. Because of this, starch or starch is converted into glucose 6-phosphate under the influence of phosphoglucomutase enzyme. Later, with the help of phosphatase enzyme, glucose 6-phosphate is converted into glucose 1-phosphate. It increases the density of guard cells. Water enters the guard cell by the process of endorespiration. The guard cell swells and bends like a bow and the stomata open.
Starch → Glucose 6-phosphate → Glucose 1-phosphate
(ii) Mechanism of stomatal closure
CO2 is produced during respiration in the guard cells at night. CO2 reacts with water to form carbonic acid. As a result the pH of the guard cell decreases. Because of this, under the influence of phosphatase enzyme, glucose 1-phosphate is converted into glucose 6-phosphate. Glucose 6-phosphate is then converted to starch/starch by the enzyme phosphoglucomutase. It reduces the density of guard cells. In the process of exudation, water escapes from the guard cells. The guard cell loses water and relaxes and the stomata close.
Glucose 1-phosphate → glucose 6-phosphate → starch/starch

In 1926, scientist Sayre presented a theory. According to him, the stomata open and close to allow the interconversion of sugars and carbohydrates and to vary the pH of the cell.
(i) Stomatal opening technique
CO2 is used in the photosynthetic process in the guard cells during the day. This decreases the CO2 concentration in the guard cells and increases the pH. Because of this, under the influence of phosphorylase enzyme, the white blood cells of the guard cells are converted into 1-phosphate. As a result, the density of the guard cell increases and water enters the guard cell by the process of endoabsorption. The guard cell takes in water and bends like a bow and the stomata open.
(ii) Mechanism of stomatal closure
CO2 is produced during respiration in the guard cells at night. CO2 reacts with water to form carbonic acid. As a result the pH of the guard cell decreases. Due to this, under the effect of phosphorylase enzyme, glucose 1-phosphate is converted into white sugar. It reduces the density of guard cells. In the process of exudation, water escapes from the guard cells. The guard cell loses water and relaxes and the stomata close.
Bleach → Glucose 1-phosphate
Glucose 1-phosphate → white matter

F. B. Salisbury and W. A. Jensen (1984) introduced abscisic theory.
(i) Stomatal Opening Mechanism
According to this theory, the concentration of CO2 in the guard cell decreases due to photosynthesis during the day. So K+ enters the guard cell. The entry of K+ increases the concentration of the guard cell and water enters the guard cell by the process of endorespiration. The guard cell takes in water and bends like a bow and the stomata open.
(ii) Mechanism of stomatal closure
Abscisic acid enters the guard cell from the mesophyll tissue during the night and K+ is released. This reduces the density of the guard cells and water escapes from the guard cells in the process of exudation. The guard cells lose water and become silent and the stomata close.

In 1908, scientist Lloyd expressed the theory about the opening and closing of stomata.
(i) Mechanism of stomatal closure
According to this theory, osmotic pressure changes for the exchange of sugar and nitrogen in the guard cell and stomatal opening and closing depend on the osmotic pressure variation. As urine is insoluble in its presence, the osmotic pressure of the sarcophagus decreases and water escapes from the sarcophagus in the process of exudation. The guard cells lose water and become silent and the stomata close.
(ii) Stomatal opening technique
Soluble sugar is produced by converting the white matter of the guard cell. This increases the density of the guard cells and water enters the guard cells by the process of endorespiration. The guard cell takes up water and swells and the stomata open.

When the osmotic pressure of the guard cell increases, water enters the guard cell and the stomata open. Again, when the osmotic pressure of the guard cell decreases, the water escapes from the guard cell and the stomata close. The guard cell wall is thick and the cellulose microfibrils are transversely arranged so that they bend upside down and open the stomata. Various theories about opening and closing of stomata are discussed.
1. Loyd’s theory
In 1908, scientist Lloyd expressed the theory about the opening and closing of stomata.
(i) Mechanism of stomatal closure: According to this theory, osmotic pressure changes for the exchange of sugar and nitrogen in the guard cell and stomatal opening and closing depend on the osmotic pressure variation. As urine is insoluble in its presence, the osmotic pressure of the sarcophagus decreases and water escapes from the sarcophagus in the process of exudation. The guard cells lose water and become silent and the stomata close.
(ii) Stomatal opening technique: Soluble sugar is produced by converting the white matter of the guard cell. This increases the density of the guard cells and water enters the guard cells by the process of endorespiration. The guard cell takes up water and swells and the stomata open.
2. Abcisic theory
F. B. Salisbury and W. A. Jensen (1984) introduced abscisic theory.
(i) Stomatal Opening Mechanism : According to this theory, the concentration of CO2 in the guard cell decreases due to photosynthesis during the day. So K+ enters the guard cell. The entry of K+ increases the concentration of the guard cell and water enters the guard cell by the process of endorespiration. The guard cell takes in water and bends like a bow and the stomata open.
(ii) Mechanism of stomatal closure: Abscisic acid enters the guard cell from the mesophyll tissue during the night and K+ is released. This reduces the density of the guard cells and water escapes from the guard cells in the process of exudation. The guard cells lose water and become silent and the stomata close.

3. Sayre’s theory
In 1926, scientist Sayre presented a theory. According to him, the stomata open and close to allow the interconversion of sugars and carbohydrates and to vary the pH of the cell.
(i) Stomatal opening technique: CO2 is used in the photosynthetic process in the guard cells during the day. This decreases the CO2 concentration in the guard cells and increases the pH. Because of this, under the influence of phosphorylase enzyme, the white blood cells of the guard cells are converted into 1-phosphate. As a result, the density of the guard cell increases and water enters the guard cell by the process of endoabsorption. The guard cell takes in water and bends like a bow and the stomata open.
(ii) Mechanism of stomatal closure: CO2 is produced during respiration in the guard cells at night. CO2 reacts with water to form carbonic acid. As a result the pH of the guard cell decreases. Due to this, under the effect of phosphorylase enzyme, glucose 1-phosphate is converted into white sugar. It reduces the density of guard cells. In the process of exudation, water escapes from the guard cells. The guard cell loses water and relaxes and the stomata close.
Bleach → Glucose 1-phosphate
Glucose 1-phosphate → white matter

4. Starch-glucose interconversion
In 1964, scientist Steward introduced the theory of starch-glucose conversion.
(i) Stomatal opening technique: CO2 is used in the photosynthetic process in the guard cells during the day. This decreases the CO2 concentration in the guard cells and increases the pH. Because of this, starch or starch is converted into glucose 6-phosphate under the influence of phosphoglucomutase enzyme. Later, with the help of phosphatase enzyme, glucose 6-phosphate is converted into glucose 1-phosphate. It increases the density of guard cells. Water enters the guard cell by the process of endorespiration. The guard cell swells and bends like a bow and the stomata open.
Starch → Glucose 6-phosphate → Glucose 1-phosphate
(ii) Mechanism of stomatal closure: CO2 is produced during respiration in the guard cells at night. CO2 reacts with water to form carbonic acid. As a result the pH of the guard cell decreases. Because of this, under the influence of phosphatase enzyme, glucose 1-phosphate is converted into glucose 6-phosphate. Glucose 6-phosphate is then converted to starch/starch by the enzyme phosphoglucomutase. It reduces the density of guard cells. In the process of exudation, water escapes from the guard cells. The guard cell loses water and relaxes and the stomata close.
Glucose 1-phosphate → glucose 6-phosphate → starch/starch

5. Ion influx theory
In 1943, scientist Imammura first discovered the role of K+ in stomatal opening. In 1959, Japanese scientists Imammura & Fujino using radioactive isotopes proved that the opening and closing of stomata is regulated by the active absorption of K+ ions.
(i) Stomatal opening technique: During the day, guard cells absorb large amounts of K+ and Cl- ions. As a result, the osmotic pressure of the guard cell increases and water enters the guard cell in the process of endosmosis. At this time the turgor pressure (TP) of the guard cell increases and the guard cell bends like a bow. As a result, the pore opens.
(ii) Mechanism of stomatal closure: K+ and Cl- ions are released from the guard cell at night. As a result, the osmotic pressure of the guard cell decreases and water escapes from the guard cell in the process of exudation. At this time the turgor pressure (TP) of the guard cell decreases and the guard cell relaxes. As a result, the stomata are closed.
6. Modern theory Proton flow theory
In 1974 scientist Lavitt published the modern theory of stomatal opening and closing. Later Raschke, (1975), Noggle, Fritz (1976) and other scientists supported this theory. This is universally accepted doctrine.
Stomatal opening technique
(i) Blue (430-460nm) light enters the guard cell during the day. Under the influence of blue light, the white matter of the guard cells is converted into phosphoenol pyruvic acid.
(ii) phosphoenol pyruvic carboxylase enzyme reacts phosphoenol pyruvic acid and CO2 to produce oxaloacetic acid.
Oxaloacetic acid is converted to malic acid under the action of (Rorr) malic dehydrogenase enzyme.
(iii) Malic acid dissociates to form hydrogen ion (H+) and malate ion [R(COO-)2].
(iv) H+ moves from the guard cell into the accessory cell and K+ from the accessory cell into the guard cell.
(v) K+ reacts with malate ions in the guard cell to form potassium malate.
(vi) Potassium malate increases the osmotic pressure of the guard cell and water enters the guard cell in the process of endosmosis. This causes swelling of the guard cells and opening of the stomata.
stomatal closure technique
(i) K+ and malate ions are produced by breakdown of potassium malate in guard cells at night.
(ii) K+ moves from the guard cell into the accessory cell and H+ from the accessory cell into the guard cell.
(iii) reacts with hydrogen ion (H+) and malate ion [R(COO – )2] in the guard cell to form malic acid.
(iv) As K+ escapes from the guard cell, the osmotic pressure of the guard cell decreases and water escapes by the process of exudation.
(v) Guard cells lose water and become silent and stomata close.

Effector of stomatal opening and closing
1. Light: Intense sunlight increases the temperature of the atmosphere and decreases the relative humidity of the air. It opens the pores. Blue light accelerates pore opening. In some CAM plants (pineapple) the stomata are open at night.
2. Relative humidity: When the relative humidity of the atmosphere is low, the stomata open faster. Again, if the relative humidity of the atmosphere is high, the stomata close.
3. Atmospheric pressure: When the atmospheric pressure is low, the stomata open and when the atmospheric pressure is high, the stomata close.
4. Potassium Ion: Potassium ion helps to open the pores.
5. Water: When water enters the guard cell, the stomata open and when water leaves, the stomata close.
6. Temperature: At high temperature the stomata widen and at low temperature the stomata narrow. Therefore, when the temperature increases, the stomata open.
7. Effect of hormones: Hormones like cytokinin, abscisic acid etc help to open pores.
8. Concentration of CO2 in air: CO2 helps open stomata. But when the concentration of CO2 is high, the stomata close.

1. The skin of green leaves and young green stems has pores. The root has no stomata.
2. Anthers are present on the lower surface of the opposite sided leaves (dicots, apple), on the upper and lower sides of the equilateral (barley, bhutra) leaves and on all sides of the equilateral (onion) leaves.
3. In flower bud, bracts, bracts and clusters or petals have leaf pores.
4. The young green fruit pods and fruits have leaf pores.
5. Stomata occur in some bryophytes and pteridophytes.
6. A floating plant (shapla) has water pores on the upper part of its leaves. However, submerged aquatic plants have no stomata.
7. The leaf pore is located inside the skin of the plant. It is called sunken. Plants such as pine, cactus, sedum, casuarina etc. have hidden leaf pores.

The stomata open, sometimes partially or fully open, sometimes closed, depending on the environment and time of day and night. This biological rhythm of the stomata is called stomatal clock. The stomata of the plant are fully open from 10-11 am and 2-3 pm. Other times are partially open.

A pore or pore surrounded by two crescent-shaped guard cells located in the leaves and young green stems of plants is called a leaf spore. The lower skin of the opposite sided leaf and the two skins of the same sided leaf have stomata. The aerial parts of plants such as leaves, shoots, petals, fruits etc. have stomata. Leaves may have 1,000-60,000 pores per square centimeter. When open, the stomata are 10-40 cm long and 3-12 cm wide.