Evaluation of nickel tolerance in Amaranthus paniculatus L. plants by measuring photosynthesis, oxidative status, antioxidative response and metal-binding molecule content

Among metals, Ni has been indicated as one of themost dangerous for the environment, and plants exposed tothis metal are frequently reported to undergo a severe stresscondition. In this work, the tolerance responses to different Niconcentrations at physiological and biochemical levels wereevaluated in Amaranthus paniculatus L., a plant species previouslycharacterised for their ability to phytoremove Ni frommetal-spiked water. Results indicated a good metal toleranceof this plant species at environmentally relevant Ni concentrations,while clear symptoms of oxidative damages weredetected at higher Ni concentrations, both in roots and leaves,by measuring lipid peroxide content. At the photosyntheticlevel, pigment content determination, chlorophyll fluorescenceimage analysis and gas-exchange parameter measurementsrevealed a progressive impairment of the photosyntheticmachinery at increasing Ni concentrations in the solution.Regarding biochemical mechanisms involved in antioxidativedefence and metal binding, antioxidative enzyme (ascorbateperoxidase, APX; catalase, CAT; guaiacol peroxidase, GPX;superoxide dismutase, SOD) activity, polyamine (PA) content,polyamine oxidase (PAO) activity and organic acid (OA)content were differently affected by Ni concentration in thegrowth solution. A role for GPX, SOD, PAs, and oxalic andcitric acid in Ni detoxification is suggested. These results cancontribute to elucidate the tolerance mechanisms carried outby plants when facing environmentally relevant Ni concentrationsand to identify some traits characterising the physiologicaland biochemical responses of Amaranthus plants to thepresence and bioaccumulation of Ni.