Phytotoxic effects of bulk and nano-sized Ni on Lycium barbarum L. grown in vitro - Oxidative damage and antioxidant response.

This study aimed to evaluate the effects of nickel oxide nanomaterial (nano-NiO) on goji berry (Lycium barbarum L.) shoots grown under in vitro conditions and to determine if the nanomaterial was more harmful than its bulk counterpart, nickel (II) sulphate (NiSO4). For this purpose, in vitro shoots of L. barbarum were cultured on MS medium supplemented with 15 mg L-1 of NiSO4 or nano-NiO. Nano-NiO was more harmful for shoots growth and photosynthetic pigments than NiSO4, with reductions up to 82% in comparison to the control. Shoots treated with nano-NiO presented an overproduction of hydrogen peroxide (H2O2; 130% increase) and superoxide anion (O2-; 110% increase), which led to higher levels of lipid peroxidation (LP; 57% increase) and the occurrence of oxidative stress. In opposition, bulk Ni seemed not to induce oxidative stress, once LP and reactive oxygen species content decreased in comparison with the control. The evaluation of the non-enzymatic antioxidant (AOX) system revealed that, under nano-NiO excess, proline, ascorbate, glutathione and phenols levels increased up to 4-fold, but did not change in response to the bulk treatment. With respect to the enzymatic AOX system, nano-NiO enhanced the activities of superoxide dismutase (203%) and ascorbate peroxidase (62%), though catalase activity was negatively affected, while bulk Ni did not majorly affect these enzymes' behavior. Overall, the data showed that Ni phytotoxicity in L. barbarum shoots depends on the metal source and that, in this case, nano-NiO seemed to be more deleterious to goji shoots grown under in vitro conditions than NiSO4.