Expression of heavy metal ATPases (HMA1 and HMA3) in Brassica nigra and B. juncea grown at different Cu levels

Metal pollution is a major environmental problem which affects agriculture and human health. Turkey has significant Cu mining areas in Diyarbakır and its surrounding areas (Southeast Anatolia). Several crop plants cultivated in these areas are irrigated with water from the Tigris, and most agricultural lands are contaminated with Cu. Brassica nigra and B. juncea are well-known metal accumulator plant species which can hyperaccumulate metals, including copper, in their shoots. The purpose of this study is to evaluate their potential for the phytoremediation of Cu from these contaminated areas as an environmentally friendly and cost-effective means of reducing Cu-contamination. In this research, B. nigra and B. juncea plants were grown in soil at different Cu concentrations (0 to 1000 µM) and showed no toxicity symptoms while accumulating a significant amount of metal in their leaves. In the leaves of both species, the Cu content increased significantly with the increase in the Cu level in the media. HMA1 (Heavy Metal ATPase 1) in the leaves of both plant species gradually increased with increased Cu levels until 50 μM, then its expression slowly decreased with the further increase in Cu levels. The expression of HMA3 also increased with an increase in Cu in the leaves of both plant species. However, its expression pattern differed from that of HMA1. Our data showed that an increase in Cu levels in the leaves triggers the expression of both genes, suggesting that they play an active role in Cu detoxification. We propose that these plant species could be used for the decontamination of Cu from polluted soils. These data also indicate that Cu accumulation and tolerance in both plant species is probably a multi-genetic response, possibly involving several other transporter genes in the stress signal pathway. Hence, we also explored the expression of the other metal transporters, such as other HMAs (HMAs 5‒8), Nramps (e.g., Nramp3), COPT proteins, and some Cu chaperons in these plant species.