Isolated cell walls exhibit cation binding properties distinct from those of plant roots

The principal contributor to the cation binding properties of roots is currently considered to be the cell wall or, alternatively, the plasma membrane. The aim of this study was to highlight their respective contributions in the binding properties. Cell walls of a dicotyledon (Solanum lycopersicum L.) and monocotyledon (Triticum aestivum L.) were isolated from roots and their binding properties were compared to those of their respective roots. Cell wall and root binding capacities were evaluated by potentiometric titrations and cation exchange capacity measurements, while their biochemical composition was analyzed by C-13-NMR spectroscopy. The lower binding capacity of isolated cell walls compared to roots revealed that cell plasma membranes had a higher binding site density than cell walls. The significant decrease in some NMR signals, i.e. carbonyl C, N alkyl/methoxyl C and alkyl C regions, suggested that carboxyl, amine and phosphate binding sites, borne by proteins and phospholipid plasma membranes, contribute to the binding capacity. Cell walls and plasma membranes were found to be jointly involved in root binding properties and their respective contributions seemed vary between plants.