Abstract
BackgroundBecause of the increasing quantity and high toxicity to humans of polycyclic aromatic hydrocarbons (PAHs) in the environment, several bioremediation mechanisms and protocols have been investigated to restore PAH-contaminated sites. The transport of organic contaminants among plant cells via tissues and their partition in roots, stalks, and leaves resulting from transpiration and lipid content have been extensively investigated. However, information about PAH distributions in intracellular tissues is lacking, thus limiting the further development of a mechanism-based phytoremediation strategy to improve treatment efficiency.ResultsPyrene exhibited higher uptake and was more recalcitrant to metabolism in ryegrass roots than was phenanthrene. The kinetic processes of uptake from ryegrass culture medium revealed that these two PAHs were first adsorbed onto root cell walls, and they then penetrated cell membranes and were distributed in intracellular organelle fractions. At the beginning of uptake (< 50 h), adsorption to cell walls dominated the subcellular partitioning of the PAHs. After 96 h of uptake, the subcellular partition of PAHs approached a stable state in the plant water system, with the proportion of PAH distributed in subcellular fractions being controlled by the lipid contents of each component. Phenanthrene and pyrene primarily accumulated in plant root cell walls and organelles, with about 45% of PAHs in each of these two fractions, and the remainder was retained in the dissolved fraction of the cells. Because of its higher lipophilicity, pyrene displayed greater accumulation factors in subcellular walls and organelle fractions than did phenanthrene.ConclusionsTranspiration and the lipid content of root cell fractions are the main drivers of the subcellular partition of PAHs in roots. Initially, PAHs adsorb to plant cell walls, and they then gradually diffuse into subcellular fractions of tissues. The lipid content of intracellular components determines the accumulation of lipophilic compounds, and the diffusion rate is related to the concentration gradient established between cell walls and cell organelles. Our results offer insights into the transport mechanisms of PAHs in ryegrass roots and their diffusion in root cells.
Highlights
Because of the increasing quantity and high toxicity to humans of polycyclic aromatic hydrocarbons (PAHs) in the environment, several bioremediation mechanisms and protocols have been investigated to restore PAH-contaminated sites
Two primary processes are responsible for PAH transfer and distribution in plant tissues: (1) transfer between plant tissues and cells driven by transpiration and the PAH concentration gradient across plant-cell components and (2) accumulation of PAHs in plant tissues, with the extent related to plant lipid contents [18,19,20,21]
The slower rate of pyrene reduction after 100 h indicates that pyrene is recalcitrant to metabolism in roots and that, as the more lipophilic compound, it exhibits a strong affinity for plant tissues, slowing its transport from roots to shoots
Summary
Because of the increasing quantity and high toxicity to humans of polycyclic aromatic hydrocarbons (PAHs) in the environment, several bioremediation mechanisms and protocols have been investigated to restore PAH-contaminated sites. The transport of organic contaminants among plant cells via tissues and their partition in roots, stalks, and leaves resulting from transpiration and lipid content have been extensively investigated. Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic contaminants (POPs) that are ubiquitous in the environment [1,2,3] Their toxicity (e.g., mutagenic, carcinogenic) and potential of accumulation in biota have led to concern about their fate and transport in the environment [4,5,6]. Wild et al (2005) investigated the distributions of anthracene and its metabolites in Zea mays and suggested that the metabolism of anthracene occurs predominantly in the cell wall [24]
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