Chapter 25 - The ecophysiology, genetics, adaptive significance, and biotechnology of nickel hyperaccumulation in plants

Abstract

Plants found on serpentine soils provide model systems to investigate adaptations to extreme environments. Serpentine soils are poorly developed, prone to drought conditions, often poor in essential nutrients such as phosphorous and calcium, and rich in heavy metals such as nickel and chromium. Although exposure to high concentrations of heavy metals commonly results in toxicity in metal-intolerant plants, serpentine-tolerant plants have evolved tolerance against such deleterious effects and, in some cases, even use toxic metals to their advantage. The most common adaptations for metal tolerance are exclusion, where the plant excludes the uptake of metal ions into sensitive tissues, and accumulation, where the plant actively uptakes high concentrations of the metal and stores it within its tissues, including in leaf and phloem. A plant is deemed a “hyperaccumulator” if it maintains a high tissue concentration of a certain metal above a set threshold determined to be toxic to most plants growing in normal soils. In this chapter, we will focus on nickel hyperaccumulation, which is the best understood example of this phenomenon in the plant kingdom. In recent years, a wealth of information about this unusual physiological process has resulted from cutting-edge experiments, which have begun to elucidate the physiology, biochemistry, and genetics of nickel hyperaccumulation. These findings have already been applied to practical uses of hyperaccumulators in large-scale bioremediation efforts (i.e., in phytoremediation), as well as in eco-friendly mining practices (i.e., in agromining).