IntroductionAlthough heavy metals are toxic at high concentrations because of the damage they cause to plant metabolism, some metal-tolerant plants accumulate heavy metals within their aboveground tissues at high concentrations without any symptoms (Psaras et al., 2000;Pilon-Smits, 2005). Nickel hyperaccumulator plants are the largest group of metal hyperaccumulator plants with over 400 taxa, and the genus Alyssum L. (Brassicaceae) is the representative of this group with more than 50 nickelhyperaccumulating species (Broadhurst et al., 2009). The accumulated Ni concentration reaches nearly 3% of the leaf dry biomass in many Alyssum species (Krämer et al., 1996;Altınözlü et al., 2012).Serpentine soils are rich in heavy metals including nickel, cobalt, and chromium and are low in nutrients because they are derived from ultramafic rocks; therefore, a unique flora spreads out on such soil types (Prasad, 2005).Turkey is one of the major centers of hyperaccumulator plants as over half of the Alyssum species and over half of the hyperaccumulators are found in Turkey (Reeves and Adıgüzel, 2008). Alyssum murale Waldst. & Kit. and A. corsicum Duby are endemic to serpentine soils throughout Mediterranean Europe and are the species most often subjected to phytoremediation and phytomining studies because of their ability to grow in different types of soils (Brooks et al., 2000;Broadhurst et al., 2004). Plants hyperaccumulating heavy metals draw attention with the complex mechanisms they use to avoid the toxicity of heavy metals and where they accumulate such levels of heavy metals within the plant. Plants have a regulated system that consists of metal transport, chelation, transfer, and sequestration activities, all of which contribute to the uptake, distribution, and detoxification of metal ions (Clemens, 2001).