Physiological and Root Exudation Response of Maize Seedlings to TiO2and SiO2Nanoparticles Exposure

How the NPs effect the growth and physiological response like the release of organic acids along the root exudates is largely unknown yet. In this study, the effects of titanium dioxide (TiO2) and silicon dioxide (SiO2) nanoparticles (NPs) treatments (1000 mg/L) on maize seedlings for 6 days were examined. Plant biomass, pigment, malondialdehyde (MDA), reactive oxygen species (ROS) production, and contents of organic acids in root exudates were analyzed. SiO2NPs significantly reduced (p< 0.05) shoot length, roots, and shoot fresh weight. TiO2NPs showed significant differences (p< 0.05) in pigment contents compared to the CK. Chlorophyll a, b, total chlorophyll content, and chlorophyll/carotenoid ratio decreased by 27.8%, 29%, 28.1%, and 46.1%, respectively, while the content of carotenoid increased by 33.6% (p< 0.05). As concerns SiO2NPs treatment, there was no significant increase (p> 0.05) in chlorophyll a content compared to the CK, while chlorophyll b increased by 28.9% (p< 0.05), and chlorophyll a/b ratio and content of carotenoid decreased by 16.8% and 54.7% (p< 0.05), respectively. MDA content significantly diminished in roots and leaves under SiO2NPs. However, O2·ˉ production increased in roots by 17.2% and 23.8% (p< 0.05), respectively, under TiO2and SiO2NPs treatment. The pH of root exudates was declined by 17.4% and 14.2% (p< 0.05) respectively under both NPs treatment. Organic acid contents under TiO2NPs significantly heightened (p< 0.05) by 60.7%, 31.2%, and 50.5% for citric, lactic, and fumaric acid, respectively, while formic and oxalic acid decreased by 27.8% and 26.4% respectively compared to the CK. In SiO2NPs case, oxalic acid increased by 41.1% (p< 0.05), while malic and citric acid decreased by 62.6% and 45.7% respectively compared to the CK. In conclusion, both NPs treatments showed alternative impacts on maize seedlings.