An integration of physiology, transcriptomics, and proteomics reveals carbon and nitrogen metabolism responses in alfalfa (Medicago sativa L.) exposed to titanium dioxide nanoparticles.

ABSTRACT

Nanoparticle (NP) pollution has negative impacts and is a major global environmental problem. However, the molecular response of alfalfa (Medicago sativa L.) to titanium dioxide nanoparticles (TiO2 NPs) is limited. Herein, the dual effects of TiO2 NPs (0-1000 mg L-1) on carbon (C) and nitrogen (N) metabolisms in alfalfa were investigated. The results showed that 500 mg L-1 TiO2 NPs (Ti-500) had the highest phytotoxicity in the C/N metabolizing enzymes; and it significantly increased total soluble sugar, starch, sucrose, and sucrose-phosphate synthase. Furthermore, obvious photosynthesis responses were found in alfalfa exposed to Ti-500. By contrast, 100 mg L-1 TiO2 NPs (Ti-100) enhanced N metabolizing enzymes. RNA-seq analyses showed 4265 and 2121 differentially expressed genes (DEGs) in Ti-100 and Ti-500, respectively. A total of 904 and 844 differentially expressed proteins (DEPs) were identified in Ti-100 and Ti-500, respectively. Through the physiological, transcriptional, and proteomic analyses, the DEGs and DEPs related to C/N metabolism, photosynthesis, chlorophyll synthesis, starch and sucrose metabolism, and C fixation in photosynthetic organisms were observed. Overall, TiO2 NPs at low doses improve photosynthesis and C/N regulation, but high doses can cause toxicity. It is valuable for the safe application of NPs in agriculture.