6.4 Integration of “Omics” Tools for Developing Plants
for Phytoremediation
By their nature, plants display their importance in remediating a polluted environment via different mechanisms such pollutant uptake through efficient root systems,
accumulating pollutants inside the system, metabolizing them either alone or by
microbial assistance, stabilizing pollutants, and volatilizing them out by photorespiration. Before the arrival of advanced technologies such as omics, science considered plants more visible than the microbial systems; later, the mechanisms behind
phytoremediation were revealed by studying their genetic mechanisms, and also
their molecular variability even in the same individual. High-throughput comparative analysis reveals interplant variability without focusing on single plant characteristic features such as genes and protein metabolism, which may assist researchers
in selecting plant varieties and cultivation (Schmitz et al. 2013).
6.5 Plant Mechanisms for Metal Detoxification
In microbe-assisted phytoremediation, plants and microbes must stabilize, resist, or
tolerate the heavy metals encountered in their systems. It is a natural phenomenon of
adaptation to a stressed environment such as HMs by the plants via triggering its
physiological or molecular mechanisms when exposed. A few of the mechanisms for
adaption were found to be plant cell wall binding, transporting metals into the active
vacuolar systems and intracellular complexations via chelating ligands such as
phytochelatins and metallothioneins, as well as metal–siderophore complex sequestration into the root apoplasm or rhizosphere (Miransari 2011). Low molecular weight
organic acids (LMWOAs) are exudates by plants enhancing microbial growth, solubilizing insoluble metal nutrients such as P, Zn, and Fe, and also used to detoxify
metals such as As, Pb, and Cd by many of the metal-accumulating plants (Tu et al.
2004; Li et al. 2013). It is one of the best strategies by a plant for tolerating or excluding
metals and metalloids via chelation in the apoplast or rhizosphere, preventing their
entry into the cell symplast (Lena and Rao 1997; Magdziak et al. 2011).
6.6 How Do PGPR Combat Heavy-Metal Stress
It is very difficult to remove HMs from polluted sites as these are ultimately not
destructible or not degraded biologically, because speciation and bioavailability vary
according to the environmental changes whereas their other counterparts may
undergo biodegradation by being less bioavailable, less mobile, and less toxic. Zn,
Cu, and Ni (Olson et al. 2001; Li et al. 2013) are micronutrients essential for plants,
animals, and microbes, but other metals such as Cd, Hg, and Pb are found to not have
4 Recent Advances in Phytoremediation of Toxic Metals from Contaminated. . .
97
for Phytoremediation
By their nature, plants display their importance in remediating a polluted environment via different mechanisms such pollutant uptake through efficient root systems,
accumulating pollutants inside the system, metabolizing them either alone or by
microbial assistance, stabilizing pollutants, and volatilizing them out by photorespiration. Before the arrival of advanced technologies such as omics, science considered plants more visible than the microbial systems; later, the mechanisms behind
phytoremediation were revealed by studying their genetic mechanisms, and also
their molecular variability even in the same individual. High-throughput comparative analysis reveals interplant variability without focusing on single plant characteristic features such as genes and protein metabolism, which may assist researchers
in selecting plant varieties and cultivation (Schmitz et al. 2013).
6.5 Plant Mechanisms for Metal Detoxification
In microbe-assisted phytoremediation, plants and microbes must stabilize, resist, or
tolerate the heavy metals encountered in their systems. It is a natural phenomenon of
adaptation to a stressed environment such as HMs by the plants via triggering its
physiological or molecular mechanisms when exposed. A few of the mechanisms for
adaption were found to be plant cell wall binding, transporting metals into the active
vacuolar systems and intracellular complexations via chelating ligands such as
phytochelatins and metallothioneins, as well as metal–siderophore complex sequestration into the root apoplasm or rhizosphere (Miransari 2011). Low molecular weight
organic acids (LMWOAs) are exudates by plants enhancing microbial growth, solubilizing insoluble metal nutrients such as P, Zn, and Fe, and also used to detoxify
metals such as As, Pb, and Cd by many of the metal-accumulating plants (Tu et al.
2004; Li et al. 2013). It is one of the best strategies by a plant for tolerating or excluding
metals and metalloids via chelation in the apoplast or rhizosphere, preventing their
entry into the cell symplast (Lena and Rao 1997; Magdziak et al. 2011).
6.6 How Do PGPR Combat Heavy-Metal Stress
It is very difficult to remove HMs from polluted sites as these are ultimately not
destructible or not degraded biologically, because speciation and bioavailability vary
according to the environmental changes whereas their other counterparts may
undergo biodegradation by being less bioavailable, less mobile, and less toxic. Zn,
Cu, and Ni (Olson et al. 2001; Li et al. 2013) are micronutrients essential for plants,
animals, and microbes, but other metals such as Cd, Hg, and Pb are found to not have
4 Recent Advances in Phytoremediation of Toxic Metals from Contaminated. . .
97