Plant Roots, Environmental Remediation and Biochemical Manufacturing

Abstract

Plant roots hold a large potential for environmental remediation and bio-manufacturing. Recently developed phytoremediation technology exploits the innate ability of plants to concentrate, degrade or immobilize environmental pollutants in soils and waters. Two subsets of phytoremediation, which use plant roots to efficiently absorb and transport toxic heavy metals are approaching commercialization: (I) Phytoextraction, in which specially selected high biomass metal-accumulating plants and appropriate soil amendments are used to transport and concentrate metals from the soil into above-ground shoots which are subsequently harvested and (II) Rhizofiltration, in which roots of hydroponically grown plants, precipitate and concentrate toxic metals from polluted effluents. The metals targeted for phytoremediation include lead, cadmium, chromium, arsenic and various radionuclides. Progress has been made in understanding the biological mechanisms of phytoremediation and metal uptake, accumulation and resistance in plants. Genetic approaches which improve phytoremediation of metals have also been developed. Roots can also reduce valuable compounds and secrete them into the environment, in a process termed rhyzosecretion. Chemical and physical treatments, which mimic various stresses encountered by a plant, stimulate roots to produce and exude arrays of new compounds. Different plant species constantly synthesize and exude unique compounds whose chemical composition or function has never been determined. Secreted compounds may include valuable natural products and proteins, both native and transgenic. As one of the applications of rhizosecretion technology, tobacco roots were engineered to produce and continuously secrete several heterologous recombinant proteins. In all cases rhizosecretion did not alter the biological activity of the recombinant protein recovered from the hydroponic medium. The yield of a single plant product produced via rhizosecretion over time may exceed the weight of the plant producing it. In addition, the purification of individual compounds or proteins produced via rhizosecretion is a relatively simple task compared to tissue extraction methods. © 1999, Japanese Society for Plant Cell and Molecular Biology. All rights reserved.