Direct Observation of Organic Contaminant Uptake, Storage, and Metabolism within Plant Roots

Abstract

Vegetation plays a key role in the environmental cycling and fate of many organic chemicals. A compound's location on or within leaves will affect its persistence and significance; retention in surface compartments (i.e., the epicuticular wax and cuticle) renders the compound more susceptible to photodegradation and volatilization, while penetration into the epidermal cell walls or cytoplasm will enhance susceptibility to metabolism. Here, for the first time, methodologies which combine plant and PAH autofluorescence with two-photon excitation microscopy (TPEM) are used to visualize and quantify compound photodegradation on and within living plant leaves. Anthracene,fluoranthene, and phenanthrene were introduced to living leaves of Zea mays and monitored in real time, in control treatments, and when subject to UV-A radiation. Compound photodegradation was observed directly; different degradation rates occurred for different compounds (anthracene > fluoranthene > phenanthrene) and in different locations (at the leaf surface > within the epidermal cells). Results suggest that photodegradation on vegetation may be a more important loss mechanism for PAHs than previously thought. Compound fate in vegetation is potentially highly complex, influenced by diffusion into and location within leaf structures, the rates of supply/loss with the atmosphere, exposure to sunlight, and other environmental conditions. The techniques described here provide a real-time tool to advance insight into these issues.

Different uptake pathways between hydrophilic and hydrophobic compounds in lateral roots of <i>Cucurbita pepo</i>

“…A previous study that involved the live imaging of maize and wheat roots for uptake of anthracene and phenanthrene, kinds of polycyclic aromatic hydrocarbons, demonstrated that such hydrophobic compounds localized in the cortex of the exposed living roots. 26) This study is partially consistent with our results for perylene uptake in the respect of its passage through the epidermis, whereas the previous researchers could not detect the radial movement of their compounds to inner tissues beyond the cortex. In addition to differences in the experimental conditions, the thickness of their root samples might make it difficult to detect fluorescence in such deep areas, thus causing the different findings between our study and theirs.…”

Uptake and Acropetal Translocation of Polycyclic Aromatic Hydrocarbons by Wheat (Triticum aestivum L.) Grown in Field-Contaminated Soil

“…Two-photon excitation microscopy coupled with autofluorescence (TPEM-AF) has provided a powerful technique that enables the visualization and tracking of how organic pollutants are taken up into plants and how they behave once within the living plant tissues (13). Wild and his coworkers have pioneered the use of this technique to track the uptake and movement of PAH inside living plant leaves (14) and roots (15). They observed that for root uptake the PAHs anthracene and phenanthrene initially bound to the epidermis along the zone of elongation, passing through the epidermal cells to reach the cortex within the root hair and branching zones of the root.…”

Interactions of mixed organic contaminants in uptake by rice seedlings

“…The need for better understanding the mechanism and influential factors on plant uptake has prompted a series of studies on the plant-uptake process in recent times (Riederer, 1990;Paterson et al, 1994;Trapp, 1995;Trapp and Mathies, 1995;Burken and Schnoor, 1997;Weiss, 2000;Li et al, 2002Li et al, , 2005Wild et al, 2005). Analyses of the concentrations of nonionic contaminants in plants in relation to the external levels in water (or soil solution) from extensive sources have revealed that these contaminants enter plants largely via a passive (i.e., partition) process (Briggs et al, 1982;Chiou et al, 2001;Trapp, 2004;Su and Zhu, 2006).…”

“…Analyses of the concentrations of nonionic contaminants in plants in relation to the external levels in water (or soil solution) from extensive sources have revealed that these contaminants enter plants largely via a passive (i.e., partition) process (Briggs et al, 1982;Chiou et al, 2001;Trapp, 2004;Su and Zhu, 2006). The magnitude and efficiency of plant uptake depends in principle on contaminant level and properties, plant species/composition, exposure time, and other variables (Briggs et al, 1982;Chiou et al, 2001;Trapp, 2004;Wild et al, 2005). Previously, we have studied the uptake of atrazine by rice seedlings from nutrient solution with and without coexisting organic and metal-ion species (Su et al, 2005;Su and Zhu, 2006).…”