what is k+ ion theory
Answers
Explanation:
POTASSIUM ION PUMP THEORY
The main features of the theory were put forward by Levitt (1974). Levitt explained the influx of K+ in the guard cells and their role in the stomatal movement. He demonstrated a relationship between stomatal opening and accumulation of K+ ions. According to the hypothesis, pH of the guard cells rises due to active uptake of H+ ions by guard cell. The steps involved are as follows.
The light induced proton transport from the cytoplasm into the chloroplast creates a negative potential. This negative potential may lead to influx of positively charged K+ ion from the surrounding cells so that the negative potential is decreased and the proton transport is not ceased. This results in the development of maximum pH.
The pH of cytoplasm is raised to 8-9 and that of the chloroplast is lowered to 5. The rise in the pH causes hydrolysis of starch to form organic acid especially phospho enol pyruvate. Phospho enol pyruvate in the presence of enzyme PEP carboxylase combines with CO2 to produce oxalic acid. This acid is then converted to malic acid.
Malic acid disassociates into H+ ion and malate ion. H+ ions comes out and in exchange K+ ions enter into the guard cells, thereby increasing the concentration of K+ ion and decreasing the H+ ions in guard cells. This is an active ionic exchange and requires ATP and cytokinin.
The pH of the cell sap in the guard cells increases simultaneously. The pH becomes more than 7 and the medium becomes alkaline.
There is also an increased uptake of Cl- anions by the guard cells to maintain the electrical and ionic balance inside and outside guard cells.
The malate anions formed in the guard cells are neutralized by the K+ ions. K+ ions react with malate to form potassium malate.
Potassium malate enters into the cell sap reducing the water potential and increasing the osmotic concentration and osmotic pressure of the cell sap.
Endosmosis occurs and the guard cells become turgid and the stoma opens.
Answer:
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Following steps takes place in the Potassium Pump Theory:
1. In the guard cells, starch is converted into malic acid in presence of light (during day time).
2. Protons formed are used by the guard cells for the uptake of K+ ions. This is an active ionic exchange and requires ATP energy and cytokinin.
3. The concentration of K+ ions increases in guard cells.
4. At the same time, the concentration of H+ ions decreases in guard cells. The pH of the cell sap in guard cells also increases simultaneously (pH becomes more than 7).
5. There is also an increased uptake of CI- by the guard cells to maintain the electrical and ionic balance inside and outside the guard cells.
6. The malate anions formed in the guard cells are neutralized by the K+ ions. This results in the formation of potassium malate.
7. Potassium malate enters the cell sap of the guard cells thereby reducing the water potential while increasing the osmotic concentration and the osmotic pressure of the cell sap.
8. Hence, endosmosis occurs.The guard cells become turgid and kidney-shaped and the stomata opens.