Impact of ZnSO4-and ZnO Nanoparticles on Seed Germination and Seedling Growth of Lettuce

Micronutrient nanoparticles (NPs) are currently an option for chemical fertilization and biostimulation in crops. However, there is little information on the phytotoxic or biostimulatory effects of NPs at low concentrations of some elements, such as Zn. In this study, the effect of low concentrations of Zn oxide (ZnO) NPs on germination, growth variables, and nutritional attributes of lettuce (Lactuca sativa L.) was evaluated in comparison to Zn sulfate. Romaine lettuce seeds were treated with ZnSO4- x 7H2O and ZnO NPs at Zn molar concentrations of 1 x 10-3, 5 x 10-3, 1 x 10-4, 5 x 10-4, 1 x 10-5, 5 x 10-5, 1 x 10-6, and 5 x 10-6. The seeds treated with ZnSO4- at 5 x 10-6 registered the highest radicle length, 73% more than the control treatment. The seeds treated with ZnSO4- at 5 x 10-3 registered the lowest values, with 50% less than the control treatment. ZnO NPs at 5 x 10-6 significantly increased content of chlorophyll A and B and total phenolics. These results indicate the possible existence of a mechanism related to the intrinsic nanoparticle properties, especially at low concentrations.