Heavy metals and plants – model systems and hyperaccumulators

Commentary Heavy metals and plants – model systems and hyperaccumulators Understanding how plants accumulate and store metal ions is relevant to two important applications: metal nutrition – for humans and in agriculture; and metal detoxification – using plants as biological detoxification systems for the 'phytoremediation' of metal contamination in the environment. Metal ions, such as Cu, Fe, Zn and Se, are essential nutrients for which deficiencies in animal and human diets cause significant disorders. These, in addition to other non-essential metals, such as Cd, Hg, Pb, Al and As, can cause toxicities when present in excess. Knowing how organisms regulate essential metal ion metabolism will contribute to improvements in essential metal ion nutrition for animals and humans. Similarly, knowledge of the mechanisms by which metals, both essential and nonessential, can be seques-tered, stored and detoxified in various organisms may contribute to the optimisation of phytoremediation processes (Clemens et al ., 2002). In plants these two aspects of metal metabolism have been described as opposite sides of the same coin (Guerinot & Salt, 2001). This issue of New Phytologist highlights research in the field of metal metabolism and detoxification in plants. It includes a number of articles spanning the breadth of research in the field, from reviews of nonplant model organisms used to inform aspects of plant biology, to the genetic and physiological analysis of metal hyperaccumulation and tolerance, to investigations of ecological aspects of metal accumulation. Often neglected is an understanding, not of the mechanisms of metal tolerance, but of the precise mechanisms of metal toxicity. This is illustrated in a Tansley review by Rengel & Zhang (pp. 295– 314), which provides comprehensive coverage of the effects of Al toxicity on the important functions of Ca ions in plants. Other papers explore the potential use of poplars in phytoremediation (see Di Baccio et al ., pp. 443– 452), important ecological aspects of metal accumulation and toxicity, particularly the influence of metal hyperaccumulation on herbivory (Huitson & Macnair, pp. 453– 459, Hanson et al ., pp. 461 – 469) and a rare study of developmental asymmetry as a possible measure of environmental metal toxicity (Batterham et al ., 471 – 477). Here, I will focus on recent developments in the molecular genetic analysis of metal metabolism in plants. Numerous aspects of plant biology, not least metal metabolism , have advanced dramatically with the adoption of Ara-bidopsis thaliana as a model organism …