Application of oxide nanoparticles mitigates the salt-induced effects on photosynthesis and reduces salt injury in Cyclocarya paliurus

Salinization is very detrimental to photosynthetic processes and plant growth, while nanoparticles (NPs) are considered to be the emerging materials to improve plant adaptability to salt stress. Cyclocarya paliurus is being planted on saline-alkali soils to meet the growing demand for its leaves and medicinal products. However, this species exhibits low salt tolerance and little information is available on whether NPs application would mitigate the salt-induced effects. This study explored the influence of three oxide NPs and their application doses on improving salt tolerance in C. paliurus under simulated natural conditions. The results showed that these oxide NPs could modify the salt tolerance in C. paliurus seedlings, but the alleviating effects varied in the NPs types and their application doses. Under the salt stress, foliar applications of SiO2-NPs with 500 mg L-1 and MnO2-NPs with 50 mg L-1 significantly increased net photosynthetic rate and seedling height by 52.0-59.5 %, and reduced the salt injury index by 67.6-70.7 %. Transcriptomic analysis revealed that the genes related to photosynthesis pathway were well responsive to both salt stress and NPs application, while the applications of high-dose SiO2- and MnO2-NPs up-regulated the expression of 50 photosynthesis-related genes. Weighted gene co-expression network analysis (WGCNA) indicated there existed a close relationship between physiological parameters and gene expression patterns, and the nine key genes in mitigating salt stress in C. paliurus were identified after the NPs application. Our findings suggested that the effects of NPs on mitigating salt-induced damages depending on the NP type and applied dose. The applications of SiO2-NPs and MnO2-NPs with an appropriate dose hold great promise for mitigating the salt-induced photosynthetic dysfunction via regulation of related key genes, and ultimately promoting plant growth and ameliorating the salt-tolerance.