Enhancement of soybean nodulation by seed treatment with non–thermal plasmas

Abstract

Soybean (Glycine max (L.) Merrill) is one of the most important crops worldwide providing dietary protein and vegetable oil. Most of the nitrogen required by the crop is supplied through biological n 2 fixation. Non-thermal plasma is a fast, economical, and environmental-friendly technology that can improve seed quality, plant growth, and crop yield. Soybean seeds were exposed to a dielectric barrier discharge plasma operating at atmospheric pressure air with superimposed flows of O 2 or n 2 as carrying gases. An arrangement of a thin phenolic sheet covered by polyester films was employed as an insulating barrier. We focused on the ability of plasma to improve soybean nodulation and biological nitrogen fixation. The total number of nodules and their weight were significantly higher in plants grown from treated seeds than in control. Plasma treatments incremented 1.6 fold the nitrogenase activity in nodules, while leghaemoglobin content was increased two times, indicating that nodules were fixing nitrogen more actively than control. Accordingly, the nitrogen content in nodules and the aerial part of plants increased by 64% and 23%, respectively. Our results were supported by biometrical parameters. The results suggested that different mechanisms are involved in soybean nodulation improvement. Therefore, the root contents of isoflavonoids, glutathione, auxin and cytokinin, and expansin (GmEXP1) gene expression were determined. We consider this emerging technology is a suitable pre-sowing seed treatment. Soybean (Glycine max (L.) Merrill) crop is considered a highly valuable source of protein, oil, and biofuel. With a worldwide sown area of 130 million hectares, soybean production achieved 370 million metric tons (68% of global production) in 2018-2019, up 9 percent from the previous year. Approximately 45% of this production corresponds to South American countries: Argentina, Brazil, and Paraguay 1. Growers in the main agricultural areas of the world employ chemical fertilizers as the only reliable tool for facing the increasing demand for food that accompanies the ever-growing world population 2. There is a substantial concern around the world for the optimization of alternative nitrogen sources that may help to avoid the intensification of chemical fertilizer usage. The contribution of biological nitrogen fixation (BNF) to the stock of N available for the crop results essential. The symbiotic associations between legumes and rhizobia represent the most important N 2-fixing agents in agricultural systems. Soybean is considered among the most efficient legume species regarding the ability to fix N: 58-68% of soybean plant N derives from N 2 fixation 3. Only bacteria contain the nitrogenase enzyme that can reduce N 2 to ammonium, and the major problem in maintaining a high rate of N 2 fixation is that this enzyme is oxygen-labile 4. Leghaemoglobin accumulated in the cytoplasm of infected plant cells binds to free oxygen avoiding the inactivation of nitrogenase 5. Many scientific efforts have been made in the last de...

Seed treatment with cold plasma and electromagnetic field induces changes in red clover root growth dynamics, flavonoid exudation, and activates nodulation

“…Decreased content of daidzein, genistein, and daidzin in roots of soybean seedlings has been determined previously, [ 28 ] while according to results, the amounts of many flavonoids were increased in red clover root exudates (Figure 4). It is pertinent to note that the amounts of compounds exuded to rhizosphere depend not only on their biosynthesis and their content in the root but also on the diverse proteins mediating their sequestration, release, and transport, [ 46,47 ] such as passive transport systems and active systems, including ABC‐transporters, as well as apoplastic β‐glucosidases, which release isoflavones from their conjugates making them available for transport.…”

“…Soybean seeds were inoculated with nitrogen‐fixing Bradyrhizobium strain before sowing and used to grow seedlings in sterilized vermiculite. [ 28 ] We found that the number of root nodules increased after red clover seed treatment with CP and EMF, although we did not inoculate seeds and the seedlings were grown in multipurpose potting substrate; thus, nodular rhizobacteria originated either from red clover seeds or from the substrate, as they would in natural conditions. We did not observe any substantial effects on the growth of the above‐ground part of young (5‐week‐old) plants in this study, but we suppose that a large increase in red clover biomass production obtained after 5 months [ 20 ] can be explained by CP‐ and EMF‐stimulated nodulation and nitrogen fixation activity.…”

“…It was shown recently that CP (dielectric barrier discharge plasma) stimulated nodulation in the roots of soybean and activated biological nitrogen fixation: The nitrogenase activity and leghemoglobin content in nodules was enhanced, indicating that nodules were fixing nitrogen more actively than in control. [ 28 ] The authors concluded that an increase in nodulation and nitrogen fixation results in better plant growth and improved plant biometrical parameters. Soybean seeds were inoculated with nitrogen‐fixing Bradyrhizobium strain before sowing and used to grow seedlings in sterilized vermiculite.…”

“…[ 30,31 ] In line with this, it has been demonstrated that the treatment of soybean seeds with dielectric barrier discharge plasma enhances nodulation and activates biological nitrogen fixation by nodular rhizobacteria. [ 28 ] Such findings provide an additional explanation for the strong positive long‐term effects of seed treatments with CP on plant growth, biomass, and harvest.…”

Increased germination of barley and wheat using cold plasma

“…In practice, various types of seeds treatment are used, such as heating, exposure to high frequency currents, etc. [1][2][3][4][5].…”