Low surface negativity of root protoplasts from aluminum-tolerant plant species

Five plant species differing in aluminum (Al) tolerance, i.e., rice, oats, maize, pea, and barley, were used and the relationship between the surface negativity of root protoplasts and Al tolerance was investigated. The protoplasts in the final stage of purification were viable, and devoid of cell wall residues. The surface negativity of the root protoplasts was tested by their stainability with methylene blue. The stainability with methylene blue was widely different among the root protoplasts even from the same root portion, and the root protoplasts stained with methylene blue aggregated with the lapse of time. Zeta potential of root protoplasts from all the plant species was in the range of –52 to –12 mV, and wide differences were observed among the values of the zeta potential of root protoplasts even from the same root portion of the same plant species. We observed that the average zeta potential of the root protoplasts was high in the Al-tolerant plant species; at low pH, the root protoplasts with a low zeta potential were abundant in the apical portion of the younger roots. These results suggest that the negativity of the plasmalemma of the root cells may determine the extent to which Al binds to the plasmalemma of root cells and finally the Al tolerance of the plant species. © Taylor & Francis Group, LLC.