The role of roots and rhizosphere in providing tolerance to toxic metals
and metalloids
Abstract
Human activity and natural processes have led to widespread
dissemination of metals and metalloids, many of which are toxic and have
a negative impact on agronomic production. Roots, as the first point of
contact, are essential in endowing plants with tolerance to excess
metal(loid) in the soil. The most important root responses include:
adaptation of transport processes that affect uptake, efflux and long
distance transport of metal(loid)s; metal(loid) detoxification within
root cells via conjugation to thiol rich compounds and subsequent
sequestration in the vacuole; plasticity in root architecture; the
presence of bacteria and fungi in the rhizosphere that impact on
metal(loid) bioavailability; the role of root exudates. In this review
we will provide details on these processes and assess their relevance
for the detoxification of arsenic, cadmium, mercury and zinc.
Furthermore, we will assess if any of these methodologies has been
tested in field conditions and whether they are effective in terms of
improving crop metal(loid) tolerance.