Copper binding by the root cell walls of Italian ryegrass and red clover

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Abstract
The amounts of Cu bound by the root cell walls of Italian ryegrass and red clover supplied with 5.0 ppm Cu for 3 or 6 days were examined by desorption and chemical fractionation experiments. Furthermore, the maximum Cu-binding capacity (MCBC) of the root cell wall fraction prepared from the roots without Cu supply was determined in different ranges of pH and ionic strength. Desorption by 0.1 N HCl for 10 min removed 67% (Italian ryegrass) and 60% (red clover) of the total Cu in the roots. Chemical fractionation of the Cu- supplied roots also showed that about 60% of the total root Cu was bound by the root cell walls and plasma membranes. The value of MCBC was markedly affected by the pH and ionic strength of the external solution: the value increased with the increase of the solution pH and decreased under a high ionic strength. Based on the results on chemical fractionation of the Cu-supplied roots and the MCBC values at pH 4.5 under an ionic strength of 0.01, it was considered that the sites for Cu-binding of the cell walls were saturated with Cu2+ after 6 days of treatment with 5.0 ppm Cu.