Soil-Weathered CuO Nanoparticles Compromise Foliar Health and Pigment Production in Spinach (Spinacia oleracea)

In this study, spinach plants exposed to fresh/unweathered (UW) or weathered (W) copper compounds in soil were analyzed for growth and nutritional composition. Plants were exposed for 45 days to freshly prepared or soil-aged (35 days) nanoparticulate CuO (nCuO), bulk-scale CuO (bCuO), or CuSO4 at 0 (control), 400, 400, and 40 mg/kg of soil, respectively. Foliar health, gas exchange, pigment content (chlorophyll and carotenoid), catalase and ascorbate peroxidase enzymes, gene expression, and Cu bioaccumulation were evaluated along with SEM imagery for select samples. Foliar biomass was higher in UW control (84%) and in UW ionic treatment (87%), compared to the corresponding W treatments (p <= 0.1). Root catalase activity was increased by 110% in UW bCuO treatment as compared to the W counterpart; the value for the W ionic treatment was increased by 2167% compared to the UW counterpart (p <= 0.05). At 20 days post-transplantation, W nCuO-exposed plants had similar to 56% lower carotenoid content compared to both W control and the UW counterpart (p <= 0.05). The findings indicate that over the full life cycle of spinach plant the weathering process significantly deteriorates leaf pigment production under CuO exposure in particular and foliar health in general.