Maize seedling root exudation, growth and physiological alterations induced by the toxicity of zinc oxide nanoparticles.

The widespread production and release of ZnO nanoparticles (NPs) in the environment may have affected on living and nonliving ecosystem components. In this study, the effects of ZnO NPs on the growth, photosynthetic pigments, oxidative damage and organic acid in the root exudates of 7 days hydroponically grown maize seedlings were examined. The results showed that ZnO NPs treatment significantly reduced the growth of seedlings compared to the control (CK). No substantial differences were found among the content of chlorophyll, while the carotenoid was 34% lower and chlorophyll/carotenoid ratio was 63% higher in ZnO NPs treated seedlings in comparison to the CK. The content of malondialdehyde (MDA) both in the roots and leaves have no significant changes between the ZnO NPs treatment and the CK. However, the content of H2O2 in the roots was diminished by 68.6% under ZnO NPs treatment compared to the CK, while there was no significant change in the leaves between two treatments. Besides, O2˙ˉ production in the roots and leaves increased under ZnO NPs treatment by 50.5% and 48.6%, respectively, compared with the CK. The pH of root exudates decreased by 6.1 % suggesting that the rhizosphere was acidified under the treatment of ZnO NPs. The amount of organic acids decreased significantly in the root exudates under ZnO NPs treatment by 25.5%, 34.4%, 58.8%, 64.8%, 91.2%, and 93.5% for citric, lactic, formic, tartaric, oxalic and malic acid, respectively, compared with the CK. In addition, fumaric acid augmented by 2.03 folds under ZnO NPs treatment compared with the CK. Taken together, ZnO NPs treatment decreased maize seedlings growth, content of carotenoid except the ratio of chlorophyll to carotenoid, increased O2˙ˉproduction in both roots and leaves. Except fumaric acid, all other organic acids in the root exudates decreased under ZnO NPs treatment compare to the CK. [ABSTRACT FROM AUTHOR]