Modification of pectin distribution in sunflower (Helianthus annuus L.) roots in response to lead exposure

The pectic component is an integral part of the plant cell wall and plays an important role in plant growth. The structure and composition of the cell wall depends on the type of cell in particular organs and can be modified by environmental factors. Due to the interaction between the roots and rhizosphere, the cell wall components, including pectin, are the first constituents which react to a toxic rhizosphere ingredient - lead. The aim of this study was to evaluate the effect of lead treatment on pectic polysaccharide occurrence in roots, especially on the distribution of homogalacturonan with low vs. high levels of methyl-esterification in the cells of the root cap, quiescent center, and elongation zone. Moreover, a quantitative analysis of the galacturonic acid content and the amount of ruthenium red binding were performed. The obtained results indicate the effect of lead on arrangement of pectin in roots growing at different toxic ion concentrations. We found a correlation between the increasing lead concentration and the distribution of specific epitopes of methylated (JIM7) and un-esterified (JIM5) homogalacturonan. Overall, the toxic lead ion concentration exerted an impact on the content of homogalacturonan with low and high levels of esterification in all investigated root zones.