ИСТИНА

Acid-base properties and swelling capacity of suaeda (Suaeda altissima L. Pall), spinach (Spinacia oleracea L., Matador cv.) and chickpea (Cicer arietinum L.) root cell walls were investigated under different salinity condition. The roots of green plants of different age were analysed 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 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 (Stan) groups were determined in the root cell walls. For suaeda plants the quantity of acidic groups (fixed anions) was shown to be nearly half as much as that for chickpea. It was found that in the plant root cell walls, there are 3 cation-exchange groups (two types of carboxyl groups and phenolic group) and one anion-exchange group (amine group) in root cell walls. The quantity of functional groups of each type (Sj) was estimated, and the corresponding values of pKaj were calculated. The Stcat and Stan as well as Sj were demonstrated to be are stable at any pH and electrolyte concentration (CNa+) of the medium. The values of pKaj and Sj indicate that the root cell walls of the chickpea, spinach and suaeda are identical in qualitative structure of ionogenic groups but vary in the quantity of each ionogenic group. It was shown that for all types of cation exchangeable groups arranged in cell wall structure the acid properties are enhanced by the increasing of electrolyte concentration. For each ionogenic group the coefficients of Helfferich's equation pKaj = f (CNa+) were determined. It was found that swelling of root cell walls changes with pH, CK+ and strongly depends on plant species. In the pH and CNa+ range covered the swelling coefficient varies in the following sequence: chickpea > spinach > suaeda. The results indicate that for tested plant species such sequence of change in swelling is connected with (a) different cross-linked degree of the polymeric chains arranged in cell wall structure, (b) different summarized quantity of carboxyl groups and (c) different total quantity of functional groups. It has been demonstrated, that for the suaeda the cross-linked degree of the polymeric chains in root cell walls is higher in comparison with that for the spinach or chickpea. Based on known data and experimental results of present study it was concluded that the change in cell wall swelling in response to variances of environmental or initial conditions leads to the change in volume water flow through the plant roots. It has been emphasized that the resulting parameters (Sj, pKaj, Kcw) and the dependencies {pKaj = f (CK+), Kcw = f (CK+, pH)} allow to estimate quantitatively the ion exchange capacity of root cell walls in response to changes in an ionic composition of an outer medium. The results of this investigation point to the fact that both the transport of mineral solutes within the apoplast and the volume water flow through the plants are highly sensitive to environmental influence on the ion exchange properties of plant root cell walls. The work was supported by the Russian Foundation for Basic Research (project No 04-04-49379).