Can Stress Enhance Phytoremediation of Polychlorinated Biphenyls?

Abstract

Phytoremediation-plant-facilitated remediation of polluted soil and groundwater-is a potentially effective treatment technology for the remediation of heavy metals and certain organic compounds. However, contaminant attenuation rates are often not rapid enough to make phytoremediation a viable option when compared with alternative treatment approaches. Different strategies are being employed to enhance the efficacy of phytoremediation, including modification to the plant genome, inoculation of the rhizosphere with specialized and/or engineered bacteria, and treatment of the soil with supplementary chemicals, such as surfactants, chelators, or fertilizers. Despite these efforts, greater breakthroughs are necessary to make phytoremediation a viable technology. Here, we introduce and discuss the concept of integrating controlled environmental stresses as a strategy for enhancing phytoremediation. Plants have a diverse suite of defense mechanisms that are only induced in response to stress. Here, we examine some stress-response mechanisms in plants, focusing on defenses involving physiological changes that alter the soil microenvironment (rhizosphere), and outline how these defense mechanisms can be co-opted to enhance the effectiveness of phytoremediation of polychlorinated biphenyls and other contaminants.

FIG. 1.

Schematic drawing illustrating changes in plant physiology in response to environmental stress. Nitrogen deficiency (N ): increased lateral root elongation. Phosphorous deficiency (P ): increased fine root hair production, which may promote growth of polychlorinated biphenyls-degrading microorganisms. Aluminum stress: citric and other organic acids exuded, stimulating growth of the rhizoshphere. Grazing/parasite stress: phenolic compounds synthesized both in roots and leaves. (A) Fine root hair with background concentrations of phenolic compounds. (B) Phenolic content of root hairs increases before senescence. (C) After senescence of fine-root hair, phenol-metabolizing bacteria have increased presence in the rhizosphere due to the phenolic loading from fine root hair turnover. Adapted from Lopez-Bucio et al. (2003).