Germination and Growth Improvement of Some Micro-Greens under the Influence of Reactive Species Produced in a Non-Thermal Plasma (NTP)

Micro-greens or sprouts are commonly used in the diet of many cultures owing to their health benefits. In this work we use a non-chemical solution method to stimulate the germination and growth of seeds used for sprouting, based on non-thermal plasma discharge (NTP). Such a technology could represent an alternative not only for reducing the production costs for growing micro-greens but also as a pre-sowing method for slow germinating species or those under draught stress. To evaluate the efficiency of the treatments, Brassica oleracea and Lepidium sativum seeds were exposed to a non-thermal plasma discharge produced in atmospheric air in different conditions. The strongest modifications were recorded when the discharge was produced in a closed environment when the reactive species produced in air remained in high concentrations near the seeds. The garden cress exhibited stronger modifications, with a decreasing of the water contact angle of the seeds by up to about 14%, which means an increase of the hydrophilicity of the surface of the seeds. The stimulation of the growth was evaluated as an increase of the average stem length of (9 +/- 0.4)% and of the root length of (38 +/- 0.5)% as compared to sprouts grown from untreated seeds. This indicated that the reactive species were not only interacting with the surface of the seeds as proved by electron microscopy imaging but also penetrated inside the seeds, activating biological pathways that lead to the stimulation of growth in this case. A noticeable influence produced by the reactive species was also reflected in the biochemical results, where the analysis of the chlorophyll pigments indicated strong modifications, especially under the intensified action of the reactive species. The results prove an important contribution from the reactive species and show the possibility of using this technology to improve the growth of these micro-greens, reducing production time and even presenting the possibility of treating packaged seeds.