Absorption, distribution, and transformation of TNT in higher plants

Abstract

The ability of eight species of plants to assimilate 2,4,6-trinitrotoluene (TNT) was investigated. Glycine max (soybean), in particular, demonstrated rapid assimilation of high concentrations of this explosive. Penetration and localization of [1- 14C]-TNT in plant root cells and leaves were studied via electron microscopic autoradiography. TNT was shown to be localized primarily on membrane structures involved in the transportation of nicotinamide coenzymes (membranes of endoplasmic reticulum, mitochondria, plastids). [1- 14C]-TNT in roots was incorporated mainly in low-molecular-weight metabolites; however, in stems and leaves, the radiocarbon was incorporated in biopolymers. Enzymatic transformation of TNT in roots was studied, and it was found that degradation involved mainly nitroreductase acting on the TNT nitro groups. The process was intensified in the presence of electron donors—NADH and NADPH. Nitroreductase activity was revealed in root cell cytosol and expression was strongly induced by plant cultivation on TNT-containing media. Oxidation of [C 3H 3]TNT by peroxidase and phenoloxidase was also studied. In contrast to the strongly induced nitroreductase, levels of these enzymes changed very little with TNT addition. This suggests that the main pathway of TNT transformation in plant cells is nitro group reduction. A plant's nitroreductase activity and its ability to incorporate TNT from aqueous solutions were correlated in four plants that were studied. The results suggest that plant nitroreductase activity may serve as a good biochemical indicator of plants that can be used for phytoremediation of soils contaminated with TNT.