Page 76 - Plant-Based Remediation Processes

64 O.P. Abioye et al.

Physical Effects - Transpiration of volatiles
hydraulic control of dissolved plume

Phytodegradation - Metabolism within the
plant production of the dehalogenase and
oxygenase enzymes, which help catalyze
degradation

Accumulation in roots
translocated to shoots
and leaves

Enhanced
Rhizosphere
Biodegradation

Fig. 4.1 Mechanism for phytoremediation (Source: United States Environmental Protection
Agency 2000)

concentration gradient from root apex can be observed (Tung and Temple 1996;
Seregin et al. 2004). Indeed, the highest lead concentrations can be found in root
apices, where root cells are young and have thin cell walls (with the exception of
root cap cells) that facilitate root uptake (Tung and Temple 1996; Seregin et al.
2004). Moreover, the apical area is the area where rhizodermic pH is the lowest,
which increases solubility of lead in the soil solution. At the molecular level, the
mechanism by which lead enters roots is still unknown. Lead may enter the roots
through several pathways, and a particular pathway is through ionic channels.
Although lead uptake is a nonselective phenomenon, it nonetheless depends on
the functioning of an H+/ATPase pump to maintain a strong negative membrane
potential in rhizoderm cells (Hirsch et al. 1998; Wang et al. 2007). Inhibition of lead