Ion Exchange Properties of Plant Root Cell Wallsстатья

Статья опубликована в высокорейтинговом журнале

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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.

Работа с статьей

[1] Meychik N. R., Yermakov I. P. Ion exchange properties of plant root cell walls // Plant and Soil. — 2001. — Vol. 234, no. 2. — P. 181–193. Acid-base properties and the swelling capacity of wheat, lupin and pea root cell walls were investigated. Roots of seedlings and 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 ionic strength (between 0.3 and 1000 mM). To analyse the polysigmoid titration curves pHi = f (Si), the Gregor’s equation was employed. It was shown that the Gregor’s model fits well the experimental data. The total number of the cation exchange (Stcat) and the anion exchange (Stan) groups were determined in the root cell walls. The number of acidic groups (fixed anions) for leguminous plants was shown to be nearly half of those for cereals. It was shown that in conformity with our earlier results obtained for seedling as well as for plant, three cation-exchange groups (two different carboxyl groups and one phenolic group) and one anion-exchange amine group were found in the root cell walls at various solution ionic strength. The number of the functional group of each type (Sj) was estimated, and the corresponding values of pKaj were calculated. It was found that Stcat and Stan as well as the number of functional group of each type did not change significantly with pH and electrolyte concentration (CK+). The values of pKaj and Sj indicate that the root cell walls of wheat, lupin and pea are identical in qualitative structure of ionogenic groups but vary in the amount of each group. It was shown that for all types of cation exchangeable groups arranged in the cell wall structure the acid properties are enhanced by the increasing concentration of electrolyte. For each ionogenic group the coefficients of Helfferich's equation [pKaj = f (CK+)] were determined. It was found that the swelling of root cell walls changes with pH, CK+ and strongly depends on plant species. Within the experimental pH and CK+ range the swelling coefficient changes as follows: lupin  pea  wheat. The obtained results show that for the plant species under investigation the differences in the swelling coefficients originate from (a) the differences in the cross-linking degrees of polymeric chains arranged in the cell wall structure, (b) the differences in the number of carboxyl groups and (c) the differences in the total number of functional groups. Based on the estimated swelling coefficients in water it could be inferred that for wheat the cross-linking degree of the polymeric chains in the root cell walls is higher than those for lupin or pea. On the basis of the literature review and the results of the present experimental study it was proposed that the changes in the cell wall swelling in response to variances of environmental or experimental conditions could lead to a change of the water flow through a plant root. It has been emphasized that the calculated parameters (Sj, pKaj, Kcw), the equation {pKaj = f (CK+)} and the dependencies {Kcw = f (CK+, pH)} allow to estimate quantitatively the changes in the ion exchange capacity of the root cell walls in response to the changes in an ionic composition of an outer solution. The results of these estimations allow to suggest that (a) the root apoplast is a compartment where the accumulation of cations takes place during the first stage of cation uptake from an outer medium, (b) the accumulation degree is defined by pH and ionic composition of an outer solution. It has been supported that there is direct relationship between the swelling of root cell walls and the water flow within the plant roots.

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