Question

k+ concentration theory

Answer 1

K+ ion theory was proposed by Levitt in 1974. He states that:- During light:- Starch is converted to PEP ( phosphoenol pyruvic acid) which combines with CO to form oxaloacteic acid (OAA) and ánally to malic acid. This malic acid dissociates into malate anions and H ions in guard cells. H ions are transported to subsidiary cells and in exchange of which K ion move inside guard cells. This is called ion exchange. K ions are balanced by malate ions present in guard cells and also by taking in some Cl ions. This ion exchange occurs by the expenditure of ATP energy. Increased concentration of K and malate ions in the guard cells vacuole, will cause sufácient osmotic pressure to absorb water from surrounding cells. This in turn will increase turgor pressure of guard cells and lead to the opening of stomatal pores. During dark:- Carbon-dioxide concentration increase in sub-stomatal spaces because of initiation of respiration which will prevent the H - K ion exchange. Due to this malate ions present in the vacuole of guard cells combine with the H+ ions and form malic acid. Increase in the concentration of malic acid will inhibit its synthesis. K ion move out of guard cells, osmotic pressure decrease. Water will move out of guard cells into subsidiary cells which makes cell âaccid and cause the closure of stomatal pore