Seed Nanopriming with Green-Synthesized Cu-Based Nanoparticles for Maize Plants with Improved Tolerance to Hydric Stress

Nanopriming with green-synthesized nanoparticles (NPs) has the potential to optimize crop performance under different conditions. This work investigated the implications of nanopriming of maize seeds with green-synthesized Cu-based NPs (ascorbic acid/starch, ACu, and green tea extract, GTCu) on the nutritional and morphophysiological traits of maize plants. Seeds Zea mays cv. Balu 787 were treated with different concentrations (14.5, 29, 58, and 116 mg Cu L–1) of both NPs, compared to hydropriming (CONT) and unprimed seeds (TEST). In a laboratory, seeds were germinated under different water conditions, while the long-term effects of seed nanopriming were evaluated in a greenhouse experiment with plants under different water conditions. The ionomic profile and morphophysiological traits of the plants were evaluated. In germination with water, both NPs increased the seedling Cu content by 37%, while in germination with PEG-6000, ACu and GTCu increased germination by 53 and 131%, respectively, compared with TEST and CONT. Without water restriction, hydropriming and ACu provided higher concentrations of many elements in seedling tissues. Under water deficit, only ACu stood out compared to the other treatments. GTCu promoted nutritional imbalance in both germination conditions. Although both NPs improved the water use efficiency of plants, ACu stood out for providing a better root/shoot ratio, helping the plants to be more tolerant to water deficit. GTCu provided greater shoot growth combined with lesser induction of root growth, leading to higher susceptibility to water deficit. In both experimental conditions, the dose of 58 mg Cu L–1 was highlighted, due to the induction of the greatest effects on seedling/plant development. The results suggest differences in the adsorption/absorption of NPs, with ACu triggering more positive effects on maize plants than GTCu. Overall, this study highlights the potential contribution of green nanotechnology in inducing plant growth and tolerance to abiotic stress by seed nanopriming.