| The aim of this research was to investigate the mechanism of phytoremediation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by poplar plants and to understand the role of symbiotic bacterium Methylobacterium populi BJ001 in RDX degradation.; Microarray analysis of an Arabidopsis thaliana genome was used as a screening tool to identify RDX upregulated genes in Populus. Arabidopsis microarray results pointed out many genes possibly involved in RDX transformation. Populus homologues for eight Arabidopsis upregulated genes were identified and their expression patterns in response to RDX exposure (40 mg L-1, 0.18 mM) were investigated by reverse transcriptase real-time quantitative polymerase chain reaction (RT rt-qPCR) analysis. This approach has identified several Populus leaf genes likely involved in plant-RDX detoxification mechanisms: a 2-oxoglutarate dependent Fe(II) oxygenase gene, a monooxygenase 1 gene, a cytochrome P450 gene and two glycosyltransferase genes. Consequently, this investigation demonstrated that genome wide transcriptional analysis of Arabidopsis can be used to infer gene expression patterns in Populus.; FISH analysis and autoradiography analysis were used to investigate physical accessibility of the endosymbiont, M. populi BJ001, to RDX or its metabolites in plant tissues. Using FISH analysis, M. populi BJ001 was shown to infect and invade deep inside plant tissues and to enter and colonize within plant cells. Greater M. populi BJ001 populations were found outside plant tissues than inside, indicating their primary habitat is the surface of the plant. On the other hand, light microscopy autoradiography showed the close association of 14C-activity (RDX and its metabolites) with chloroplasts and lignified tissues in poplar leaves. Thus, M. populi BJ001 has a limited accessibility to RDX and/or its metabolites within plant tissues. Other investigations showed that poplar tissue cell cultures were not generally contaminated with bacteria including M. populi BJ001, yet mineralization of RDX by the tissue cell cultures was observed. Taken together, the results suggest that the overall contribution of M. populi BJ001 to RDX phytotransformation by poplar plant tissues is not significant. |
