Copper tolerance strategies involving the root cell wall pectins in Silene paradoxa L.

New insights were provided on the function of root cell wall pectin concentration and methylation degree in copper tolerance studying contrasting ecotypes of Silene paradoxa. A metallicolous copper tolerant population and a non-metallicolous sensitive population were grown in hydroponics and exposed to different CuSO4 treatments to evaluate copper accumulation in relation to pectin concentration and methylation degree of the root cell wall. In short-term exposure experiments the tolerant population decreased root cell wall pectin concentration and increased their methylation degree, while the sensitive population did not respond. Moreover, a positive correlation between root pectin concentration and metal accumulation in root apoplast and symplast was found. In addition, a negative correlation between pectin methylation degree and apoplastic copper concentration were found to be negatively correlated. In long-term exposure experiments, the sensitive population increased the concentration of pectins with the same methylation degree and consequently the ability of its root cell wall to bind the metal. The opposite phenomenon was shown by the tolerant population. Moreover, pectin methylation degree was higher in the tolerant population in respect to the sensitive one, possibly to limit metal binding to the root cell wall. Therefore, in the copper tolerant population of S. paradoxa the generation of metal-excluding root cell walls was suggested to be one of the factors concurring to guarantee a low apoplastic copper accumulation and probably also to limit symplastic copper uptake by the root cells. (C) 2011 Elsevier B.V. All rights reserved.