We have suggested mechanisms/models in our recent publications. Kindly download the same from my ResearchGate account. We showed likely involvement of plasma membrane bound dehydrogenases in rhizofiltration and phytostabilization. We believe that generation of heavy metal nanoparticles/nanocomplexes by plants (irrespective of exogenous means or endogenous means) is an ideal way plants can convert toxic ionic speciation state of heavy metal into less/non-toxic nanoparticle/nanocomplex speciation state. We have discussed on various mechanisms in the following publications.

Pardha-Saradhi et al. 2014 - in Biometals, RSC Advances and PLoS One.

Shabnam et al. 2014 in PLoS One.

Thank you Mr Pardha Saradhi

In addition to the excellent papers cited above, you may also check the followings:

Van Oosten, M.J., Maggio, A., Functional biology of halophytes in the phytoremediation of heavy metal contaminated soils, (2015) Environmental and Experimental Botany, 111, 135-146.

Islam, M.S., Saito, T., Kurasaki, M., Phytofiltration of arsenic and cadmium by using an aquatic plant, Micranthemum umbrosum: Phytotoxicity, uptake kinetics, and mechanism, (2015) Ecotoxicology and Environmental Safety, 112, 193-200.

Li, X., Xi, H., Sun, X., Yang, Y., Yang, S., Zhou, Y., Zhou, X., Yang, Y., Comparative proteomics exploring the molecular mechanism of eutrophic water purification using water hyacinth (Eichhornia crassipes), (2015) Environmental Science and Pollution Research, 16 p.

Anjum, N.A., Ahmad, I., Válega, M., Mohmood, I., Gill, S.S., Tuteja, N., Duarte, A.C., Pereira, E., Salt marsh halophyte services to metal-metalloid remediation: Assessment of the processes and underlying mechanisms, (2014) Critical Reviews in Environmental Science and Technology, 44 (18), 2038-2106.

Azmat, R., Moin, S., Hamid, N., Saeed, A., Nasreen, H., Qamar, N., Phytoremediation characteristics of weeds and mushrooms as a metal scavenger in restoring metal contaminated soil, (2014) Biotechnology, 13 (1), 28-31.

Viehweger, K., How plants cope with heavy metals, (2014) Botanical Studies, 55 (1),

Xie, H., Li, C., Xu, J., Li, H., The mechanism of evans blue removal by sunflower, (2014) Journal of Chemical and Pharmaceutical Research, 6 (1), 327-331.

Paz-Ferreiro, J., Lu, H., Fu, S., Méndez, A., Gascó, G., Use of phytoremediation and biochar to remediate heavy metal polluted soils: A review. (2014) Solid Earth, 5 (1), 65-75.

Mani, D., Kumar, C., Biotechnological advances in bioremediation of heavy metals contaminated ecosystems: An overview with special reference to phytoremediation.

(2014) International Journal of Environmental Science and Technology, 11 (3), 843-872.

Pinto, E., Aguiar, A.A.R.M., Ferreira, I.M.P.L.V.O., Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu, Mn, and Zn, (2014) Critical Reviews in Plant Sciences, 33 (5), 351-373.

Shahid, M., Austruy, A., Echevarria, G., Arshad, M., Sanaullah, M., Aslam, M., Nadeem, M., Nasim, W., Dumat, C., EDTA-Enhanced Phytoremediation of Heavy Metals: A Review, (2014) Soil and Sediment Contamination, 23 (4), 389-416.

Malar, S., Manikandan, R., Favas, P.J.C., Vikram Sahi, S., Venkatachalam, P., Effect of lead on phytotoxicity, growth, biochemical alterations and its role on genomic template stability in Sesbania grandiflora: A potential plant for phytoremediation, (2014) Ecotoxicology and Environmental Safety, 108, 249-257.

Duan, D.-C., Yu, M.-G., Shi, J.-Y., Research advances in uptake, translocation, accumulation and detoxification of Pb in plants, (2014) Chinese Journal of Applied Ecology, 25 (1), 287-296.

Song, Y., Hudek, L., Freestone, D., Puhui, J., Michalczyk, A.A., Senlin, Z., Ackland, M.L., Comparative analyses of cadmium and zinc uptake correlated with changes in natural resistance-associated macrophage protein (NRAMP) expression in Solanum nigrum L. and Brassica rapa, (2014) Environmental Chemistry, 11 (6), 653-660.

Guarino, C., Conte, B., Spada, V., Arena, S., Sciarrillo, R., Scaloni, A., Proteomic analysis of eucalyptus leaves unveils putative mechanisms involved in the plant response to a real condition of soil contamination by multiple heavy metals in the presence or absence of mycorrhizal/rhizobacterial additives, (2014) Environmental Science and Technology, 48 (19), 11487-11496.

Yang, J.X., Li, X.L., Gao, L., Yao, D., Zhang, M.X., Study on spatial migration law of heavy metal copper in soil-Ligustrum lucidum plant interface system, (2014) Nature Environment and Pollution Technology, 13 (1), 95-99.

Babaoǧlu Aydaş, S.S., Açik, L., Leduc, D., Adigüzel, N., Ellialtioǧlu, S.S., Suludere, Z., Kadioǧlu, Y.K., Localization and distribution of nickel and other elements in in-vitro grown Alyssum corsicum exhibiting morphological changes in trichomes: Initial insights into molecular mechanisms of nickel hyperaccumulation, (2013) Turkish Journal of Botany, 37 (6), 1115-1124.

Liu, M.C., Zhang, B., Zhou, W., Selection of tolerant plants of Cu and Ni and the enrichment mechanism, (2013) Advanced Materials Research, 726-731, 1632-1637.

Li, Z., Wu, L., Hu, P., Luo, Y., Christie, P., Copper changes the yield and cadmium/zinc accumulation and cellular distribution in the cadmium/zinc hyperaccumulator Sedum plumbizincicola, (2013) Journal of Hazardous Materials, 261, 332-341.

Leung, H.-M., Wang, Z.-W., Ye, Z.-H., Yung, K.-L., Peng, X.-L., Cheung, K.-C., Interactions between arbuscular mycorrhizae and plants in phytoremediation of metal-contaminated soils: A review, (2013) Pedosphere, 23 (5), 549-563.

Leitenmaier, B., Küpper, H., Compartmentation and complexation of metals in hyperaccumulator plants, (2013) Frontiers in Plant Science, 4 (SEP), art. no. 374, .

Lyubenova, L., Kuhn, A.J., Höltkemeier, A., Schröder, P., Root exudation pattern of Typha latifolia L. plants after copper exposure, (2013) Plant and Soil, 370 (1-2), 187-195.

Küpper, H., Leitenmaier, B., Cadmium-accumulating plants., (2013) Metal ions in life sciences, 11, 373-393.

Yang, J.-X., Zhang, M.-X., Li, X.-L., Gao, L.-M., Yao, D.-X., Migration law of heavy metal cadmium in soil-root interface systems, (2013) Journal of Coal Science and Engineering, 19 (2), 243-248.

Ali, H., Khan, E., Sajad, M.A., Phytoremediation of heavy metals-Concepts and applications, (2013) Chemosphere, 91 (7), 869-881.

Agostini, E., Talano, M.A., González, P.S., Oller, A.L.W., Medina, M.I., Application of hairy roots for phytoremediation: What makes them an interesting tool for this purpose?, (2013) Applied Microbiology and Biotechnology, 97 (3), 1017-1030.

Gupta, D.K., Huang, H.G., Corpas, F.J., Lead tolerance in plants: Strategies for phytoremediation, (2013) Environmental Science and Pollution Research, 20 (4), 2150-2161.

Ramirez-Sandoval, M., Muñiz-Hernández, S., Velázquez-Fernández, J.B., Mechanisms of phytoremediatory effect of ocimum basilicum l. and its rhizosphere exposed to different concentrations of the organochlorine pesticide endosulfan, (2013) Chemical Engineering Transactions, 34, 73-78.

Chu, L., Shao, H., Sun, J., Xu, G., Zhang, L., Yan, K., Some advances in bio-removing hazardous heavy metals from contaminated soils, (2013) Metal Contamination: Sources, Detection and Environmental Impact, 19-41.

Mudhoo, A., Lin, Z.-Q., Phytoremediation of nickel: Mechanisms, application and management, (2012) Disruptive Technologies, Innovation and Global Redesign: Emerging Implications, 173-195.

Olguín, E.J., Sánchez-Galván, G., Heavy metal removal in phytofiltration and phycoremediation: The need to differentiate between bioadsorption and bioaccumulation, (2012) New Biotechnology, 30 (1), 3-8.

Thank you so much Mr Cristian Simion