Unravelling cadmium toxicity and tolerance in plants: Insight into regulatory mechanisms

Abstract

The occurrence of heavy metals in soils may be beneficial or toxic to the environment. The biota may require some of these elements considered essentials (like Fe, Zn, Cu or Mo) in trace quantities, but at higher concentrations they may be poisonous. Due to the difficulty in controlling environmental metal accumulation, organisms have to cope with exposure to unwanted chemical elements, specially those considered biologically nonessential. Cadmium (Cd) belongs to this latter group. The effect of Cd toxicity on plants has been largely explored regarding inhibition of growth processes and decrease of photosynthetic apparatus activity. This article reviews current knowledge of uptake, transport and accumulation of Cd in plants and gives an overview of Cd-detoxification mechanisms, Cd-induced oxidative damage and antioxidant defenses in plants. It also presents a picture of the role of reactive oxygen and nitrogen species in Cd toxicity; signalling and gene regulation are topics critically discussed. This review aspires to pinpoint new avenues of research that may contribute to a more differentiated view of the complex mechanisms underlying Cd toxicity in target tissues.