Accumulation and sub cellular distribution of lead (Pb) in industrial hemp grown in Pb contaminated soil

Abstract

Industrial hemp has an excellent lead (Pb) tolerance and accumulation capacity. Further enhancing the Pb tolerance and its accumulation in industrial hemp is of great significance for its future application in phytoremediation. In present study, a pot experiment using Pb-contaminated soil was conducted to investigate the accumulation of Pb contents in various organs of industrial hemp and its subcellular distribution and extractable form in the leaves. It was found that under Pb stress, the Pb content in plants increased significantly with an increase in the soil Pb concentration. Lead was mainly concentrated in the roots, followed by stems and leaves, while the lowest Pb contents were found in seeds (<12 mg/kg). The Pb content in roots was 2–7 times higher than in stems, leaves, and fibers, and 6–25 times higher than in seeds. At the subcellular level, Pb in industrial hemp leaves was mainly distributed in the cell wall and chloroplasts, with the Pb content first increasing and then decreasingas the soil Pb concentration increased, reaching a maximum at 4000 and 3000 mg/kg, respectively. Lead was less accumulated in the vacuoles and soluble parts of cells, with the least accumulation occurring in the organelles. There was no nsignificant increase in Pb content in these subcellular locations with the increase in soil Pbconcentration. Treatments with different Pb concentrations affected the extractable form of Pb in hemp leaves. The HCl extractable form of Pb, with low activity, was predominant in the leaves. The proportional content of Pb in each form was different in the various parts of the plant. The Pb content of each form in the leaf was Pb HCl(hydrochloric acid)＞Pb E (ethanol)>Pb W (deionized water)>Pb HAc (acetic acid) >Pb NaCl (sodium chloride), indicating that Pb in industrial hemp mainly exists in the form of insoluble oxalate precipitates, thereby alleviating the toxicity of Pb. The results of this study provide a scientific reference for the use of industrial hemp to remediate Pb polluted soils.