Abstract
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 °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.
Highlights
The constant increase in population and the loss of soils due to erosion and contamination forces us to look for alternatives to increase agricultural production, with high yields, better nutritional characteristics, and less environmental impact
The above was confirmed by Itroutwar et al (2020), who reported that NZnO applied to Zea mays seeds accumulated in the endosperm region, associated with rapid starch degradation that favored the growth of the plumule and radicle, increasing the final quality of the seedlings
Germination stage (15 days after sowing (DAS)) The germination percentage of M. oleifera seeds was not modified by NZnO (Figure 2-A); differences were found in the variables of length and dry weight of plumule and radicle
Summary
The constant increase in population and the loss of soils due to erosion and contamination forces us to look for alternatives to increase agricultural production, with high yields, better nutritional characteristics, and less environmental impact. There is a set of seed pretreatment techniques that promote the germination and initial growth of seedlings, methodologies known as "seed priming" (Waqas et al, 2019). In its origins, this concept included only the action of imbibition of seeds and subsequent drying for sowing, increasing the vigor of the plants. NZnO at low concentrations promotes the production of ROS and phytohormones and the overexpression of new water channels (aquaporins), and the response is a more remarkable synthesis of antioxidant compounds and improvement in the absorption of water and nutrients, favoring the initial growth of seedlings (Santo et al, 2021). Regarding the improvement in water and nutrient absorption, which is associated with the increase in length and biomass, it has been shown that NZnO induces overexpression of the HvTip1:1 and HvPip1:1 genes, both related to the generation of aquaporins in cells (Akdemir, 2021)
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