The Effect of Gold Nanoparticles in Sodium Alginate on the Biochemical Characteristics of Garden Cress

L.) is a useful model plant for assessing the effects of chemicals released into the environment. The aim of this study was to prepare alginate gels containing AuNPs for plant exposure experiments, evaluate their physicochemical properties, and determine their effects on selected biochemical parameters of garden cress seedlings. Gold nanoparticles were synthesized in sodium alginate at an initial concentration of 50 mg/L, using xylose and maltose as reducing agents. The gels were diluted with distilled water to obtain AuNP concentrations of 5 and 25 mg/L. Garden cress seeds were placed on filter paper soaked with the tested formulations, while distilled water and sodium alginate solutions without AuNPs served as controls. After 5 days of incubation at 20 °C under light conditions, the plant material was collected and selected bioactive compounds were determined. AuNP-containing gels significantly affected the biochemical status of the seedlings. In particular, AuNPs synthesized with xylose at 25 mg/L significantly increased the contents of photosynthetic pigments and total polyphenolic compounds. All tested AuNP formulations increased the antioxidant activity of seedlings, suggesting the activation of abiotic stress-related defense responses, however, direct markers of oxidative damage were not assessed in the present study. Overall, the results indicate that alginate-based AuNPs can modify selected biochemical parameters in garden cress seedlings, and these effects depend on nanoparticle concentration and reducing sugar used during synthesis, which may be relevant for the future development of plant-targeted nanomaterials for agricultural applications.