Subcellular Distribution Of Polycyclic Aromatic Hydrocarbons In Plants

Nowadays, organic pollution is a serious environmental problem in the world. How to remediate the contaminated soils by organic contaminants including PAHs (polycyclic aromatic hydrocarbons) is of worldwide concerns. The phytoremediation is being recognized as an important, economic, safe, and available technique for organic contaminated sites. Understanding the subcellular distribution of PAHs in plant will be very helpful to elucidate the mechanisms of the transport and transformation of PAHs in plant and to clarify the localization of PAHs in cell tissue.Subcellular distribution of phenanthrene, pyrene and anthracene, as representatives of PAHs in plants were investigated. Ryegrass (Lolium multiflorum Lam.), sorghum sudanense(Sorghum sudanense (Piper)Stapf.), zea mexicana (Euchsaena mexicana Schrad.), tall fescue (Festuca arundinacea Schreb.), clover (Trifolium repens L.) were selected as tested plants, In this work, the uptake of phenanthrene and anthracene by ryegrass from culture solution was investigated using a greenhouse hydroponic experiment. Utilizing the tissue fractionation method, subcellular distribution of phenanthrene and pyrene in plant was studied. The uptake and sorption of PAHs by plant root subcellular tissues and their correlations to the compositions of root subcellular tissues were elucidated. Main results of this work were shown as follows:(1) The concentrations of PAHs in ryegrass firstly increased and decreased thereafter in the uptake duration of0-192h. While the accumulated amounts of tested PAHs by ryegrass roots and shoots increased straightly, and root and shoot concentration factors of phenanthrene and anthracene initially increased sharply and asteady state was observed thereafter in0-192h. It was notable that shoot concentrations, accumulated amounts, and shoot concentration factors of phenanthrene or pyrene were generally much lower than root. In addition, shoot concentration factors of anthracene were smaller than those of phenanthrene. The translocation of phenanthrene and anthracene from root to shoot was observed in that duration. The translocation factors (TFs) were calculated. TF values increased firstly and kept approximately steady thereafter in0-192h. However, TF values of phenanthrene and anthracene were small (less than0.026and0.009, respectively), indicating that thetranslocation of these compounds from root to shoot in ryegrass was dramatically restricted. In addition, the TF values of pyrene smaller than those of phenanthrene.(2) The concentrations of PAHs in subcellular tissues of ryegrass roots and shoots firstly increased and decreased thereafter in the uptake duration of0-240h. The subcellular distribution (%) of phenanthrene in ryegrass root tissues followed the order of cell organelle (41%-59%)>cell wall (22%-29%)>cell soluble fraction (9%-20%), irrespective of the different plants with different spiked PAH concentrations in solution. In addition, concentrations of phenanthrene in shoot cell organelle were generally64%-126%higher than those in cell wall, and about46%-56%and39%-46%of phenanthrene were observed in shoot cell organelle and cell wall. However, only about3.8%-10%were observed in shoot cell soluble fraction. This work, to our best knowledge, is a primary report on the subcellular distributions of organic contaminants in plants.(3) The sorption and uptake of phenanthrene by root sublellular tissues were compared, and both of which related to the root lipid contents. The simulated distribution constants (Kd) for the uptake and sorption of tested PAHs by root subcellular tissues were observed to positively correlate to root lipid contents. In addition, the distribution constants of root cell wall and cell organelle for phenanthrene sorption were1492.5-2154.1L/kg and1262.2-1555.8L/kg, respectively, which were higher than those for uptake results. This could be the reasons that phenanthrene was taken in by roots and subsequently translocated from roots to shoots through the transpiration streams.In addition, the decrease of phenanthrene contents in roots was also due to the plant growth dilute and degradation of PAHs in plants.