Ion exchange properties of Cicer arietinum L. root cell walls under different environmental salt conditions

Abstract

Ion exchange properties of the polymeric matrix of cell walls isolated from roots of 20-day-old Cicer arietinum L. plants grown in nutrient solution in the presence of 0.5 and 80 mM NaCl were studied by the potentiometric method. The ion exchange capacity (Si) and the swelling coefficient (Kcw) of root cell walls were estimated at various pH values (from 2 to 12) and at different means of solution ion strength (between 10 and 250 mM). To analyse polysigmoid titration curves pHi = f (Si), Gregor’s equation was used. It was shown that Gregor’s model fits quite well the experimental data. The total quantities of cation exchange (Stcat) and anion exchange (St an) groups were determined in root cell walls. It was found that in plant root cell walls there are 3 cation-exchange groups (two types of carboxyl groups and a phenolic group) and one anion-exchange group (amine group). The quantity of functional groups of each type (ΔSj) was estimated, and the corresponding values of pKa j were calculated. It has been shown that for carboxyl groups of polygalacturinic acid arranged in the cell wall structure, the acid properties are enhanced by increasing the electrolyte concentration. Swelling of root cell walls chantes with pH and NaCl concentration in the solution. The findings are discussed from the standpoint of involvement of root cell walls in plant response to salinity. Keywords: Cicer arietinum, cell wall polymeric matrix, root, ionogenic groups, pK, salinity