[Possible ways of negative influence of acid gases on plants]

The degree of negative influence of acid gases on plants is considered in dependence of their solubility in water. The linkage of water in the processes of hydration of gases forming acids can decrease the chemical potential of water in leaf apoplast. It causes the decrease in water inflow into leaf symplast. The more solubility of acid gases in water and the higher their concentration in the air, the lower water inflow from apoplast to symplast. At high concentration of toxicant water chemical potential in leaf apoplast is lower, than in symplast, and the water flows out into apoplast, i.e. plasmolis takes place. Plasmolis leads to the increase in toxicant concentration in leaf symplast and finally to the necrosis of cells. When air with acid gases are dissolving in apoplast water, "concentrating" of acid gases takes place because the acid components are more soluble in water than the main components of the air (nitrogen and oxygen). The lower acid dissociation in apoplast water, the higher speed of receipt from apoplast to symplast and even to inner cell compartments through cell membranes. It can explain why sulfur dioxide and fluoric hydrogen forming weak acids, are more toxic than nitric dioxide. Exogenous acids producing the hydrogen ions negatively influence on different metabolic processes of plants.