Physiological responses of white mustard grown in Zn-contaminated soils

Abstract

Introducing zinc (Zn) biofortified vegetables capable to thrive on Zn-polluted soils might simultaneously solve both the problems of dietary Zn deficiency and environmental Zn pollution. White mustard (Sinapis alba L.) is known to thrive on soils with high Zn concentrations, thus we aimed to determine to what extent it has physiological characteristics close to known Zn hyperaccumulators for possible use of this species in phytoremediation efforts and production of Zn-biofortified crops. To achieve this, in a pot experiment plants were grown for 7 weeks in soils with normal (25.5 mg kg−1) and excess (500 and 1000 mg kg−1) Zn concentrations and assessed for metal accumulation, enrichment, translocation and tolerance. Zn accumulated mainly in shoots (861 mg kg−1) with translocation factor of 2.5 in parallel with enhanced root H+-ATPase activity but the plant Zn bioconcentration factors were less than one. Excess soil Zn increased plant biomass and activities of some reactive oxygen species scavenging enzymes without any effects on root lipid peroxidation or leaf chlorophyll contents. Despite lack of criteria for a true Zn hyperaccumulator, white mustard exhibited significant Zn trans-location capacity with tolerance to toxic Zn concentrations in tissues as reflected from its efficient antioxidant metabolism, unaltered photosynthetic pigments under excess Zn and high aboveground biomass similar to some Zn hyperaccmulators. Accordingly, the cultivation of this species has the dual advantages of phytoremediating Zn-contaminated soils and producing Zn-biofortified vegetables.