Growth responses, metal accumulation and phytoremoval capability in Amaranthus plants exposed to nickel under hydroponics

The characterisation of plant responses tometal exposure represents a basic step to select a plantspecies for phytoremediation. In the present work, 3-week-old Amaranthus paniculatus L. plants were subjectedto nickel chloride concentrations of 0 (control),25, 50, 100 and 150 ?M in hydroponic solution for1 week to evaluate morphophysiological responses,such as biomass production and partitioning, nickelaccumulation in plants and nickel removal ability fromthe polluted solutions. The results showed a progressivedecrease in plant organ dry mass with the enhancementof nickel (Ni) concentration in the solution, suggesting agood metal tolerance at 25 ?M Ni and a marked sensitivityat 150 ?M Ni. The modification of biomass partitioningwas particularly appreciated in leaves,analysing the organ mass ratio, the total leaf area andthe specific leaf area. Amaranthus plants accumulated asignificant amount of Ni in roots exposed to the highestNi concentrations, while lower metal contents wereobserved in the aerial organs. The Ni uptake ratio wasprogressively reduced in plants exposed to increased Niconcentrations. The metal translocation from root toshoots, appreciated by the Ni translocation index,showed a far lower value in Ni-exposed plants than incontrols. Moreover, by measuring the daily Ni contentof the solutions, a lower Ni removal ability was found inAmaranthus plants at increasing Ni concentrations.Remarkably, plants exposed to 25 ?M Ni succeeded inremoving almost 60 % of the initial Ni content of thesolution showing no stress symptoms. The potential ofA. paniculatus for phytoremediation was discussed.