CONCLUSIONS
Recent research has revealed many important factors that impinge on
plant metal(loid) tolerance. Based on this knowledge, the ideal set of
root traits would combine: a low metal(loid) bioavailability, for
example by increased organic acid secretion or sorption to rhizosphere
bacteria and fungi; limited net influx of metal(loid)s, in particular
through enhanced efflux in order not to disrupt nutrient homeostasis;
optimised detoxification capacity via vacuolar sequestration in root
cells; elevated resilience to counter secondary (oxidative) stress. As
yet, most of the above properties only have been examined without regard
for important agronomic parameters such as yield. If and how combining
all or several of the above will generate synergism is another key
factor. Most importantly, we urgently need to scrutinise the efficacy of
the above strategies in an agronomically relevant setting; this is
currently at best sporadic for approaches such as the manipulation of
transport or the role of microbes in the rhizosphere, while totally
absent in other cases such as the role of cellular detoxification via
metal(loid) liganding and chelation.