Metal Remediation via In Vitro Root Cultures
The in vitro root culture and hairy roots culture represent a relative new approach for metal removal studies. Both systems are characterized by indefinite growth and genetic and biochemical stability. Higher growth rates are obtained, and the analysis of
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Metal Remediation via In Vitro Root Cultures Marı´a del Socorro Santos-Dı´az
6.1
Introduction
Some metals (Fe, Zn, Mn, Ni, Cu, and Mo) are essential for normal plant growth and development since they are nutrients and/or constituents of many enzymes and proteins. Nonessential heavy metals include As, Cd, Cr, Hg, Pb, Sb, and U. However, elevated concentration of metals can be detrimental to living organisms. They are toxic because they can replace metals in pigments or enzymes, disrupting the function of these molecules (Manios et al. 2003; Hou et al. 2007; Jayakumare et al. 2009). Heavy metals also cause oxidative stress, especially transition metals such as Fe and Cu. The toxicity of heavy metals is generally ascribed to their high affinity for nucleophilic groups. In fact, they are soft donors and will therefore readily bind to soft acceptors such as sulphydryl groups (Stohs and Bagchi 1995; Rivetta et al. 1997; Schutzendu¨bel and Polle 2002). Heavy metals are important environmental pollutants in soil, water, and air. Soil pollution differs from air and water pollution, because metals persist in the soil for a longer time than in other compartments of the biosphere (Lasat 2002). The main sources of contamination are agricultural fertilizers, pesticides, burning of fossil fuels, metalliferous mining, metallurgical industries, sewage sludge treatment, municipal wastes, and electronic industries (Wei and Zhou 2008; Wu et al. 2010). In addition to sites contaminated by human activity, other natural sources of heavy metal pollution include the mineral deposits in many regions of the planet, volcanic activity, and weathering of rocks (Carroll 1970; Hinkley et al. 2006). There are around 430 plant species known, ranging from annual herbs to perennial shrubs and trees, that accumulate metals in large amounts. These species are of interest for potential use in phytoremediation of metal-contaminated environments
M.d.S. Santos-Dı´az (*) Faculty of Chemistry, University of San Luis Potosı´, Manuel Nava 6, CP 78210 San Luis Potosı´, Mexico e-mail: [email protected] D.K. Gupta (ed.), Plant-Based Remediation Processes, Soil Biology 35, DOI 10.1007/978-3-642-35564-6_6, # Springer-Verlag Berlin Heidelberg 2013
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(Suresh and Ravishankar 2004; Ghosh and Singh 2005; Padmavathiamma and Li 2007; Capuana 2011). Generally fast growing plants with high biomass and different kinds of root systems are used to clean up the pollutants. Metal removal can be done by taking up the metals into the roots or by transporting the metals from the roots up into the leaves (Pilon-Smits and Pilon 2002; Lasat 2002; Pilon-Smits 2005; Memon and Schro¨der 2009; Zhou et al. 2012).
6.2
General Characteristics of In Vitro Culture for Metal Removal
Another approach with great potential to study the phytoremediation process and the mechanisms involved in heavy metal tolerance is the use of in vitro cultures. Using this system, the analysis of metal removal can be performed under conditions that are more easily controlled tha
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