Seed priming with ZnO nanoparticles promotes early growth and bioactive compounds of Moringa oleifera

Nanotechnology has gained importance in agricultural production systems, with various applications such as pesticides or fertilizers. The application of nanomaterials (NMs) as a pretreatment to seeds (seed priming) has positively affected plant growth and development. On the other hand, Moringa oleifera is a plant appreciated for its multiple nutraceutical properties. Therefore, the objective of this study was to evaluate the effect of pretreatment of M. oleifera seeds with ZnO nanoparticles (NZnO) (0, 0.5, 2.5, 5, 7.5, and 10 mg L-1). The study was divided into two experimental phases: the first phase consisted of evaluating germination under laboratory conditions (25 degrees C) at 15 DAS, while in the second phase, vegetative growth and bioactive compounds were evaluated at 45 DAS under greenhouse conditions. For phase one, the percentage of germination, length, and dry weight of the plumule and radicle were considered, and the vigor indices of seeds were determined. In phase two, we measured the plant height, stem diameter, fresh and dry biomass of aerial and root parts, and the concentration of photosynthetic pigments, phenolic compounds, flavonoids, vitamin C, glutathione (GSH), and antioxidant capacity (DPPH), such as the activity of antioxidant enzymes such as ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX), and phenylalanine ammonium lyase (PAL). The results showed an increase in some variables related to seed germination, with an increase of between 30 and 25% in the vigor of the seeds subjected to 2.5 and 10 mg L-1 NZnO. The photosynthetic pigments resulted in increases of between 23 and 49% for the 7.5-10 mg L-1 NZnO treatments. Regarding bioactive compounds, the increase in phenols, flavonoids and vitamin C stands out, mainly at the levels of 7.5-10 mg L-1 NZnO, where increases of up to 543% were observed with respect to the control. The enzymatic activity showed different responses to the application of NZnO, where a biphasic response (hormesis) was observed on the activity of APX and CAT activities as the levels of NZnO increased. The results show that it is possible to promote the initial growth and bioactive compounds of M. oleifera by pretreatment of seeds mainly with 10 mg L-1 NZnO.