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.