Distribution of polycyclic aromatic hydrocarbons in subcellular root tissues of ryegrass (Lolium multiflorumLam.)

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.

Variations in phthalate ester (PAE) accumulation and their formation mechanism in Chinese flowering cabbage (Brassica parachinensis L.) cultivars grown on PAE-contaminated soils

“…The subcellular distribution of organic contaminants has important effects on their accumulation, translocation, and metabolism in different plant species and cultivars (Gao et al, 2011(Gao et al, , 2013Kang et al, 2010). The first barrier that protects the protoplast against contaminant toxicity, plant cell walls, can bind organic contaminants due to cell wall components such as pectin, cellulose, hemicellulose, and lignin, restricting transport of the contaminants across cell membranes (Kang et al, 2010).…”

Polycyclic Aromatic Hydrocarbons Degradation Techniques: A Review

“…Recent advances in phytodegradation studies have come to light in the application of rye grass (Lolium multiflorum) and bermudagrass (Cynodon dactylon) in degrading alkylated two ring naphthalenes (White, Wolf, Thoma, & Reynolds, 2006). In their contribution on distribution of PAHs in sub-cellular root tissue, Kang, Chen, Gao, and Zhang (2010) and Ward, Singh, and Van Hamme (2003) had revealed that using L. multiflorium, pyrene was most adsorped in the root of the plant than other PAHs. Previous studies from Simonich andHites (1994), Bakker, Vorenhou, Sum, andKollôffel (1999) and Gao and Zhu (2004) are of the opinion that the efficiency of plant uptake and metabolism of PAHs depended on the morphology of the plant system.…”

Transportation and localization of phenanthrene and its interaction with different species of arsenic in Pteris vittata L.

“…PAHs have a relatively low solubility in water and low Henry's law constants, but are highly lipophilic and have high octanol-water partition coefficients (K ow ), while the phospholipid bilayer of the cell membrane is externally hydrophilic and internally lipophilic. The unique characteristics of the phospholipid bilayer cause internal aggregation of PAHs inside the membrane structure (Kang et al, 2010;Haritash and Kaushik, 2009). The phospholipid layer can create a hydrophobic region for accumulation of hydrophobic compounds within the cell membrane.…”

“…Studies have demonstrated that hexane, paraffins, and PAHs enter the membrane via vesicles (Sikkema et al, 1994;White et al, 1981). Kang et al (2010) investigated the subcellular distribution of pyrene and PHE in the perennial, ryegrass (Lolium perenne L.), and found that the compounds first adsorb to the cell wall of the roots, then enter the organelles within the cell via the cell membrane. Ren et al (2010) compared the transmembrane transport of four typical lipophilic organic compounds, and proposed that PAHs in the extracellular medium enter the cytoplasm in a steady flow through the partition-inverse releasebinding mechanism.…”