Salinity Improves Zinc Resistance in Kosteletzkya pentacarpos in Relation to a Modification in Mucilage and Polysaccharides Composition

Abstract

The halophyte plant species Kosteletzkya pentacarpos produces high amounts of mucilage which may play a role in heavy metal tolerance. The amount and composition of mucilage in K. pentacarpos exposed to zinc toxicity in the presence or in the absence of 50 mM NaCl was investigated. Exposure to 0.1 mM Zn had a detrimental impact on plants growth and water content. Most of Zn was accumulated in the roots of plants exposed to Zn toxicity both in the absence and in the presence of NaCl. Salinity, however, partially alleviated the toxicity of zinc, increasing the plant biomass and decreasing zinc absorption by the root. Crude mucilage content increased in all plant organs in response to Zn stress. Acid hydrolysis of crude mucilage extract revealed that the main neutral monosaccharide constituents were rhamnose, arabinose, galactose, and glucose. Zinc induced a rise in uronic acids in roots and stems but not in the leaves where a high constitutive proportion of uronic acids was observed. Meanwhile, changes were also observed in neutral monosaccharides component in different plant organs. Zinc stress increased the hemicellulose content, but decreased the lignin and cellulose content in the stem. Salinity slightly increased the cellulose content. We suggest that excessive zinc induces a modification in the composition and structure of polysaccharides and that mucilage may contribute to Zn tolerance through toxic ion sequestration.