Pb induces plant cell wall modifications - in particular - the increase of pectins able to bind metal ions level

Abstract

Low - methylesterified pectin fraction, able to bind metal ions, is the cell wall compound which participates in land and water plant cell response to toxic metals. Protonemata of Funaria hygrometrica (Hedw.), root tips of Populus tremula x P.tremuloides and Lemna trisulca fronds, were used for studying the effects of Pb on plants cell walls (CW). The study were focused on the low- methylesterified pectins level and distribution. It was carried out by immunocytochemical methods, using JIM5 antibody which recognized low- methylesterified pectins fraction - up 40%. Pb exposure resulted in the cell wall modifications in all investigated objects. The most striking result was the marked increase of the low-methylesterified pectins level. Moreover, cell walls thickenings were formed both in the moss protonemata and the poplar roots. The cell wall thickenings in both objects contained especially high level of low-methylesterified pectins. Simultaneously, cell wall thickenings accumulated extremely large and numerous Pb deposits. In many regions of the cell wall and cell wall thickenings the colocalization of low- methylesterified pectins and Pb deposits occurred. Low - methylesterified pectins level increased also in the cell walls of Lemna trisulca fronds and some of Pb deposits were colocalized with this pectin fraction in the CW. In fronds several Pb deposits occurred between plasma membrane and cell wall and only occasionally they were colocalized with low- methylesterified pectins. However, in L. trisulca - cell wall was generally thicker in response to Pb. We did not observed almost any local cell wall thickenings as in Funaria and Populus. Taken these facts together we can conclude that plant cell walls were actively and intensively modified in response to Pb. In particular, the amount of low - methylesterified pectins, able to bind toxic Pb ions, markedly increased. Simultaneously, both cell wall and cell wall thickenings were the compartments which accumulate large amount of Pb. Hence, modified cell walls appear to be a very important repository for Pb 2+ in different types of plant cells and different species. Detection of such a reaction in three different plant species and three different types of plant cells indicates that it may be more common plant tolerance strategy to Pb.