Dose-Dependent Effects of Nanoscale Forms of Humic Acids in a Hydroponic Culture of Triticum aestivum: Induction of Oxidative Stress and an Increase in the Number of Border Cells
The biological activity of humic acids in the form of nanoparticles with a size of 6.5 nm and 68 nm was studied in a hydroponic culture of Triticum aestivum L. Both smaller and larger humic nanoparticles at the studied concentrations neither inhibited root growth nor caused destructive changes in the root apexes of 2-day- old seedlings. A dose- dependent increase in the contents of markers of induced oxidative stress such as carbonylated proteins, malonaldehyde, and proline was observed in the roots of seedlings on media with humic nanoparticles. Malondialdehyde was the main product of free radical oxidation for smaller nanoparticles and carbonylated proteins – for larger ones. Oxidative stress induced by humic nanoparticles was accompanied by a dose- dependent increase in the number of free border cells and the size of the mucilaginous sheaths on the root apexes of 2-day- old seedlings. For smaller (6.5 nm) nanoparticles, these changes were much more pronounced than for larger (68 nm) nanoparticles. The results obtained allow us to consider humic nanoparticles as adaptogens: contributing to an increase in the population of border cells and the mucilaginous sheath system (as a product of the excretory activity of border cells), nanoparticles enhance the resistance of the root apex to the effects of unfavorable biotic and abiotic factors.