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Phytomanagement could be a viable alternative in areas polluted with wastes from chromium-using industries. This study investigated the ability of Silene vulgaris to take up Cr(III) and Cr(VI) with special attention on the mechanism used by this species to tolerate high doses of Cr(VI). Plants were grown semihydroponically with different concentrations of either Cr(III) or Cr(VI). A combination of synchrotron X-ray spectroscopic techniques, scanning electron and light microscopy and infrared spectroscopy were used to determine the distribution and speciation of Cr. S. vulgaris accumulated more Cr when grown with Cr(VI) resulting in an overall reduction in biomass. Starch accumulation in leaves may be attributed to an impartment between carbon utilization and assimilation resulted from stunted plant growth but not the complete inhibition of photosynthesis indicating that S. vulgaris possess tolerance mechanisms that allows it to survive in Cr(VI) rich environments. These primary tolerance mechanisms are (a) the total reduction of Cr(VI) to Cr(III) in the rhizosphere or just after uptake in the fine lateral root tips and (b) chelation of Cr(III) to the cell wall both of which reduce metal interference with critical cell functions. These mechanisms make S. vulgaris suitable for in situ remediation of Cr polluted soils.

The interaction between plant growth-promoting bacteria (PGPB) and plants can enhance biomass production and metal tolerance of the host plants. This work aimed at isolating and characterizing the cultivable bacterial community associated with Brassica napus growing on a Zn-contaminated site, for selecting cultivable PGPB that might enhance biomass production and metal tolerance of energy crops. The effects of some of these bacterial strains on root growth of B. napus exposed to increasing Zn and Cd concentrations were assessed. A total of 426 morphologically different bacterial strains were isolated from the soil, the rhizosphere, and the roots and stems of B. napus. The diversity of the isolated bacterial populations was similar in rhizosphere and roots, but lower in soil and stem compartments. Burkoholderia, Alcaligenes, Agrococcus, Polaromonas, Stenotrophomonas, Serratia, Microbacterium, and Caulobacter were found as root endophytes exclusively. The inoculation of seeds with Pseudomonas sp. strains 228 and 256, and Serratia sp. strain 246 facilitated the root development of B. napus at 1,000 µM Zn. Arthrobacter sp. strain 222, Serratia sp. strain 246, and Pseudomonas sp. 228 and 262 increased the root length at 300 µM Cd.

Plant growth promoting endophytic bacteria (PGPB) isolated from Brassica napus were inoculated in two cultivars of Helianthus tuberosus (VR and D19) growing on sand supplemented with 0.1 mM Cd or 1 mM Zn. Plant growth, concentrations of metals and thiobarbituric acid (TBA) reactive compounds were determined. Colonization of roots of H. tuberosus D19 by Pseudomonas sp. 262 was evaluated using confocal laser scanning microscopy. Pseudomonas sp. 228, Serratia sp. 246 and Pseudomonas sp. 262 significantly enhanced growth of H. tuberosus D19 exposed to Cd or Zn. Pseudomonas sp. 228 significantly increased Cd concentrations in roots. Serratia sp. 246, and Pseudomonas sp. 256 and 228 resulted in significantly decreased contents of TBA reactive compounds in roots of Zn exposed D19 plants. Growth improvement and decrease of metal-induced stress were more pronounced in D19 than in VR. Pseudomonas sp. 262-green fluorescent protein (GFP) colonized the root epidermis/exodermis and also inside root hairs, indicating that an endophytic interaction was established. H. tuberosus D19 inoculated with Pseudomonas sp. 228, Serratia sp. 246 and Pseudomonas sp. 262 holds promise for sustainable biomass production in combination with phytoremediation on Cd and Zn contaminated soils.