The Effect of Polymetallic Pollution on Ion-Exchange Properties of Barley Root and Shoot Cell Walls.

For the first time we determined the ion-exchange properties of the cell walls (CWs) isolated from roots and shoots of barley plants grown in the conditions of polymetallic pollution. The content of all the types of cation-exchange groups in the CWs was found to be considerably higher in the shoots than in the roots, which resulted in higher metal-binding capacity of the shoot CWs and higher swelling capacity of CW polymers. It was shown for the first time that the heavy metal excess causes an increase in the content of demethylated pectins in the shoot CWs.

Nonaqueous titration of amino groups in polymeric matrix of plant cell walls.

Nonaqueous titration was used for detection of free amino groups in the polymeric matrix of plant cell walls. The content of amino groups varied in the range 0.54-0.91 and total nitrogen in the range 1.0-4.2 mmol per gram dry mass of cell walls depending on the plant species. However, these data on the high content of free amino groups do not correlate with the present day concept that the nitrogen fraction in charged amino groups in plant cell wall proteins, which are assumed to be mainly amino groups of lysine and arginine residues, is about 10%. It is supposed that most detected free amino groups belong to the hydroxy-amino acids hydroxyproline and tyrosine that can be bound at the hydroxyl group with the carbohydrate part of glycoprotein or another structural cell wall polymer.

Features of ionogenic group composition in polymeric matrix of lily pollen wall.

The composition of ionogenic groups and ion-exchange capacity were studied in the polymeric matrix of cell walls isolated from the pollen grain and tissues of vegetative organs (leaves and stems) of Lilium longiflorum Thunb. The ion-exchange capacity was evaluated at different pH values and ionic strength of 100 mM. In the two-layered pollen wall and the somatic cell walls four types of ionogenic groups were found: amino groups, two carboxyl groups (represented by residues of uronic and hydroxycinnamic acids), and phenolic OH-groups. The groups of all four types are present in the intine, whereas the exine contains one type of anion-exchange and two types of cation-exchange groups. The contents of each type group and their ionization constants were determined. The qualitative and quantitative compositions of structural polymers of the pollen intine and somatic cell walls are significantly different. It is suggested that hydroxycinnamic acids should be involved in cross-linking of polysaccharide chains in both the intine and somatic cell primary walls, and such cross-links play a crucial role in the structural organization and integrity of the pollen grain wall.

Ion-exchange properties of cell walls of Spinacia oleracea L. roots under different environmental salt conditions.

Ion-exchange properties of the polymeric matrix of cell walls isolated from roots of 55-day-old Spinacia oleracea L. (Matador cv.) plants grown in nutrient solution in the presence of 0.5, 150, and 250 mM NaCl and from roots of Suaeda altissima L. Pall plants of the same age grown in the presence of 0.5 and 250 mM NaCl were studied. The ion-exchange capacity of the spinach cell walls was determined at pH values from 2 to 12 and different ionic strength of the solution (10 and 250 mM NaCl). In the structure of the root cell walls, four types of ionogenic groups were found: amine, two types of carboxyl (the first being galacturonic acid residue), and phenolic groups. The content of each type of group and their ionization constants were evaluated. The ion-exchange properties of spinach and the halophyte Suaeda altissima L. Pall were compared, and the qualitative composition of the ion-exchange groups in the cell walls of roots of these plants appeared to be the same and not depend on conditions of the root nutrition. The content of carboxyl groups of polygalacturonic acid changed in the cell walls of the glycophyte and halophyte depending on the salt concentration in the medium. These changes in the composition of functional groups of the cell wall polymers seemed to be a response of these plants to salt and were more pronounced in the halophyte. A sharp increase in the NaCl concentration in the medium caused a decrease in pH in the extracellular water space as a result of exchange reactions between sodium ions entering from the external solution and protons of carboxyl groups of the cell walls. The findings are discussed from the standpoint of involvement of root cell walls of different plant species in response to salinity.