Biological interaction levels of zinc oxide nanoparticles; lettuce seeds as case study

Seed germination is a critical stage in plant life, and recent practices use nanomaterials for the improvement of plant seed germination indices. This study was conducted to assess the effect of laboratory prepared zinc oxide nanoparticles on the physiological and biochemical changes of lettuce seeds.

Lettuce seeds were soaked in a suspension of moderately polydisperse zinc oxide nanoparticles at two different concentrations (25 ppm or 50 ppm) and shaken for 3 h at 25 °C. Seeds treatment was followed subsequently by two to three days drying at ambient conditions. Treated seeds were stored for 3-4 weeks, at ambient conditions and then tested for germination in petri dishes. Germination was observed on daily basis and seedling length was measured. After imbibition and before the start of the visible germination, seeds were examined for topography and surface analysis using the scanning electron microscope and zinc uptake was measured by using the atomic absorption spectrometry and the energy dispersive X-ray. The pattern of mobilization of biomolecules was analyzed to detect any differences among different seed groups.

There was no loss of viability for the nanoparticles treated seeds. Indeed their germination was enhanced and their biomass increased. The activated performance of the nanoparticles imbibed seeds has been found to be correlated with an increased level of Zn inside lettuce seeds. The recorded measurements show a significant enhancement of seedling length. Interaction of zinc oxide nanoparticles with lettuce seeds mediates a variation in the biochemical processes. Changes detected in treated seeds were as following: reduced levels of the total carbohydrates (including simple saccharides and polysaccharides), higher capacity of protein synthesis, an elevated level of starch as well as an increased activity of antioxidant enzymes.

Lettuce seeds primed with ZnO nanoparticles were found not only to maintain seed viability but even to exhibit a detectable level of germination enhancement compared to the control seeds. Overall, the promoted response of lettuce seeds during early stages of seed growth is encouraging for the application of ZnO NPs for seed priming for better germination indices.