Аннотация:A comparative study of the uptake of cation type dye (methylene blue) of the isolated root cell walls and of the roots of whole transpirating seedlings was performed. Seven day seedlings of the Triticum aestivum L., Zea mays L., Cucumis sativus L., Lupinus albus L. and Vigna radiata L. grown at low concentration of all nutrients (~0.2 mM) in the medium were used. We determined the amount of ionogenic groups per 1 g of dry and fresh weight of root cell walls, their swelling capacity, ion exchange capacity on methylene blue (Mcw) depending on adsorption time and diffusion coefficients of organic cation into polymeric matrix of cell walls (Dcw). It was shown that both Mcw depended on рН (or dissociation degree of the carboxyl groups), changed in accordance with the amount of the carboxyl groups per 1 g of cell walls dry weight and decreased as follows: cucumber > mungbean > lupin > wheat > corn. The results indicate that Dcw also depended on plant species and decreased in the order: lupin > mungbean > maize > cucumber > wheat. We concluded that the mechanism of methylene blue absorbing by plant root cell walls is stipulated by ion exchangeable reactions between the of methylene blue cation and carboxyl groups of cell walls, but the rate of adsorbing process is mainly defined by the diffusion methylene blue cation into the cell walls polymeric matrix.