153
are termed as phytostabilization, rhizofiltration, phytoextraction, phytovolatilization, phytostimulation and phytodegradation (Greipsson 2011; Chatterjee et al.
2013; Gupta et al. 2016a). Suitable candidate plants for phytoremediation are plants
that are capable of uptaking elements from soil in remarkably huge quantities (like
100–1000-fold higher concentrations than their normal counterparts), without
showing any indications of phytotoxicity (Reeves 2006). Plants of families like
Asteraceae, Araceae, Papilionaceae, Brassicaceae, Poaceae and Caryophyllaceae
are reported to be best candidate for phytoremediation (Gupta 2013). Tang and
Willey (2003) reported that plants from Araceae family (e.g. Lemna minor, L. gibba)
can render higher bio- removal capacity for radionuclides including U. Therefore,
phytoremediation can be used for affordable long-term treatment to remediate
radionuclide-contaminated areas (Gupta and Walther 2014; Gupta et al. 2016a).
5 Membrane Transport and Rhizosphere for Uranium
Phytoremediation
A variety of metal transporter proteins present in the plasma membranes of root cell
play significant roles in elemental transport and homeostasis. These transporters
which belong to families like zinc importer (ZIP) families (ZRT, IRT-like protein
[ZRT, zinc-regulated transporter, IRT, iron-regulated transporter]), natural
resistance- associated macrophage protein (NRAMP), cation diffusion facilitator
(CDF) family, copper transporter (COPT) heavy metal ATPase (HMA) family like
P1B-ATPases, ATP-binding cassette (ABC) transporters, ABC transporters of the
mitochondria (ATM), Ca
2+
cation antiporter (CAX), multidrug resistance- associated
proteins (MRP) and yellow-stripe-like (YSL) pleiotropic drug resistance (PDR)
transporters are well-studied transporters (Dubey 2011; Huang et al. 2012; Gupta
et al. 2013, 2016a). Cd transport from root to shoot, as, for example, in Arabidopsis
thaliana, occurs through AtZIP4 (ZIP4) proteins (Krämer et al. 2007). Proton
pumps like vacuolar proton pyrophosphatase (V-PPase) and vacuolar proton-ATPase
(V-ATPase) are important transporters for vacuolar sequestration (Dalcorso et al.
2010; Manara 2012).
Plant roots secrete a number of components (exudates) at the rhizosphere (soil–
root interface) that help to increase immensely the richness of bacterial and fungal
communities of soil (Anderson et al. 1994). Root exudates include excretions (e.g.
protons, bicarbonates, carbon dioxide, etc.), diffusates (e.g. organic acids, amino
acids, water, sugars, inorganic ions, etc.) and secretions (e.g. siderophores, mucilage, allelopathic compounds, etc.) that modify composition of soil microflora community having unique gene pool for improved metabolic capabilities (Hall 2002;
LeDuc and Terry 2005; Gupta et al. 2016a). For example, ammonium nitrate and
citric acid augmentation helps plants to have increased availability of uranium.
However, Prasad (2011) pointed out the risk of augmenting soil, which must be
done in an appropriately managed manner. Plant growth-promoting rhizobacteria
Uranium and Plants: Elemental Translocation and Phytoremediation Approaches
are termed as phytostabilization, rhizofiltration, phytoextraction, phytovolatilization, phytostimulation and phytodegradation (Greipsson 2011; Chatterjee et al.
2013; Gupta et al. 2016a). Suitable candidate plants for phytoremediation are plants
that are capable of uptaking elements from soil in remarkably huge quantities (like
100–1000-fold higher concentrations than their normal counterparts), without
showing any indications of phytotoxicity (Reeves 2006). Plants of families like
Asteraceae, Araceae, Papilionaceae, Brassicaceae, Poaceae and Caryophyllaceae
are reported to be best candidate for phytoremediation (Gupta 2013). Tang and
Willey (2003) reported that plants from Araceae family (e.g. Lemna minor, L. gibba)
can render higher bio- removal capacity for radionuclides including U. Therefore,
phytoremediation can be used for affordable long-term treatment to remediate
radionuclide-contaminated areas (Gupta and Walther 2014; Gupta et al. 2016a).
5 Membrane Transport and Rhizosphere for Uranium
Phytoremediation
A variety of metal transporter proteins present in the plasma membranes of root cell
play significant roles in elemental transport and homeostasis. These transporters
which belong to families like zinc importer (ZIP) families (ZRT, IRT-like protein
[ZRT, zinc-regulated transporter, IRT, iron-regulated transporter]), natural
resistance- associated macrophage protein (NRAMP), cation diffusion facilitator
(CDF) family, copper transporter (COPT) heavy metal ATPase (HMA) family like
P1B-ATPases, ATP-binding cassette (ABC) transporters, ABC transporters of the
mitochondria (ATM), Ca
2+
cation antiporter (CAX), multidrug resistance- associated
proteins (MRP) and yellow-stripe-like (YSL) pleiotropic drug resistance (PDR)
transporters are well-studied transporters (Dubey 2011; Huang et al. 2012; Gupta
et al. 2013, 2016a). Cd transport from root to shoot, as, for example, in Arabidopsis
thaliana, occurs through AtZIP4 (ZIP4) proteins (Krämer et al. 2007). Proton
pumps like vacuolar proton pyrophosphatase (V-PPase) and vacuolar proton-ATPase
(V-ATPase) are important transporters for vacuolar sequestration (Dalcorso et al.
2010; Manara 2012).
Plant roots secrete a number of components (exudates) at the rhizosphere (soil–
root interface) that help to increase immensely the richness of bacterial and fungal
communities of soil (Anderson et al. 1994). Root exudates include excretions (e.g.
protons, bicarbonates, carbon dioxide, etc.), diffusates (e.g. organic acids, amino
acids, water, sugars, inorganic ions, etc.) and secretions (e.g. siderophores, mucilage, allelopathic compounds, etc.) that modify composition of soil microflora community having unique gene pool for improved metabolic capabilities (Hall 2002;
LeDuc and Terry 2005; Gupta et al. 2016a). For example, ammonium nitrate and
citric acid augmentation helps plants to have increased availability of uranium.
However, Prasad (2011) pointed out the risk of augmenting soil, which must be
done in an appropriately managed manner. Plant growth-promoting rhizobacteria
Uranium and Plants: Elemental Translocation and Phytoremediation Approaches