Understanding the physiology and biochemistry of

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Understanding the physiology and biochemistry of metal accumulation in plants is important for several reasons. The main implications are that this knowledge allows the identification of agronomic practices capable of optimizing the potential for phytoremediation and permits the identification and isolation of gene responsible for the expression of the hyperaccumulating phenotypes. Thus ideal plant for the phytoremediation of any metal must have a substantial capacity for metal uptake, bioaccumulation and stability as well as durability to reduce the length of treatment as for as possible and practicable. It then follows that there is a promising alternative in the development of transgenic plants with enhanced properties of metal uptake and translocation, bioaccumulation potential and higher tolerance to toxicity. Such heightened metal bioaccumulation and tolerance could be mainly achieved by normally over expression the natural or modified genes encoding antioxidant enzymes. Several researchers have reported to date rather encouraging results using plants genetically engineered with increased cadmium tolerance and uptake for phytoremediation purposes. However, a majority of these genetically manipulated plants for phytoremediation have only been tested under strict laboratory conditions and a very scanty few have been analysed for their phytoremediation potential at field scale. Metal hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate and detoxify metals, including cadmium and other metal or metalloids hence constitute an essential pool of material for genetic modification for targeted enhancements in phytoremediation potential (Fulekar et al 2009).
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Genetic engineering modifications of the physiological and molecular mechanism of plants, cadmium uptake and tolerance have also been successfully achieved and these show promose in opening new avenues for enhancing the overall efficiency of cadmium phytoremediation (Eapen and D’souza, 2005). The possibilities for genetic engineering plants for phytoremediation is shown in the Fig. Fig. : Possibilities for genetic engineering in phytoremediation
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A number of genetically modified (transgenic) plants have been generated and tested in recent studies and they have demonstrated the merits of genetic engineering in enhancing the tolerance, uptake and /or bioaccumulation of Cadmium. Wojas et al. (2009) have demonstrated in a study first of its kind that the hetergenous expression of Arabidopsis MRP7 in tobacco ( Nicotiana tabacum var. xanthi L . ) could modify cadmium accumulation, distribution and tolerance.
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UNUSUAL ACCUMULATION OF METALIC ELEMENTS /METALLOID BY PLANTS Sources: Brown H.J.M. (1966), H eevit E.J. and Smith, T.A. (1975) Al Club moss; Hydrangea sp., tea plants As Brown algae, fern like Pteris vittata B Brown algae, Plumbaginaceae Ba Rhizopods, Brazil nut Cu Caryophyllaceae F Dichopetalum cymosum Li Thallictrum sp., Cissium Sp. Mn Ferns, Digitalis purpurea Mo Papilionaceae Ni Alyssium sp., Hybanthus floridundus Se Cruciferae, Astragalus racemosus Sr Brown algae V Amonita sp. Brown algae Zn Thlaspi calaminare
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