Supplementation with Fe3O4 and ZnO nanoparticles as a strategy for agronomic bioenrichment of lettuce and cucumber

Iron (Fe) and zinc (Zn) play a crucial role in the development of both plants and humans. In plants, the uptake and translocation of these elements to commercially important tissues depends on the application method, route, and concentration used. Therefore, supplementation with these two elements is not standardized. The objective of this study was to evaluate the effects of different Fe and Zn sources (ionic and nanometric) to determine the optimal application route and determine the appropriate concentration that promotes Fe and Zn bioaccumulation without inducing plant toxicity. Ionic sources of Fe and Zn (FeSO 4 ·4 H 2 O and ZnSO 4 ·7 H 2 O, respectively), and nanoparticles (NPs) of ZnO (50 and 250 ppm) and Fe 3 O 4 (100 and 500 ppm) were applied via drenching and foliar application on lettuce and cucumber plants grown in greenhouse. Dry biomass, biochemical variables, stress indicators and Fe and Zn accumulation were quantified in leaf tissue. In cucumbers, chlorophylls, β-carotene, and yellow pigments responded favorably (p < 0.01) to drenching with of 100 ppm Fe 3 O 4 NPs. The same treatment but via foliar application significantly increased βCA activity and decreased proline, H 2 O 2 , and MDA content by 15.2 %. In contrast, vitamin C increased (p < 0.05) with ionic forms via drenching; however, in lettuce it increased with NPs via foliar application (p < 0.05). Lettuce plants, treated with Fe 3 O 4 NPs (500 ppm) via drenching increased chlorophyll and β-carotene content (p < 0.05). ZnO and Fe 3 O 4 NPs reduced H 2 O 2 content by 38 % and MDA by 35 %, respectively, while promoting proline by 14 %. RuBisCO increased with 250 ppm of ZnO NPs applied via foliar application in both crops, with the greatest increase documented in cucumber (50 %). No differences were observed in Fe and Zn accumulation. However, 100 ppm of Fe 3 O 4 NPs via drenching increased Fe content by 80 %, and 250 ppm of ZnO NPs via foliar application increased Zn content by 26 %, compared to the control. For lettuce, high doses of Fe 3 O 4 NPs and ZnO NPs via foliar application increased Fe and Zn content by 26 % and 45 %, respectively. The foliar-applied NPs showed the greatest accumulation, without inducing toxicity. Therefore, they are a potential tool for agronomic bioenrichment of lettuce and cucumber. • Fe 3 O 4 and ZnO nanoparticles did not induce toxicity in lettuce or cucumber. • The application route, concentration, and form of differentially impacted crops. • Supplementation mechanisms significantly affected the accumulation of Fe and Zn.