Effects Of Titanium Dioxide Nanoparticles On The Photosynthesis And Metabolism In Rice (Oryza Sativa L.)

Nano-TiO2 possesses the character of photocatalytic activity thereby affects the key process of crops photosynthesis,including light energy absorption and photosynthetic electron transfer,and disturb the related metabolic pathways,which finally affect the crops growth.Photosynthesis is the basis of matter and energy,and it plays a decisive role in maintaining the balance of metabolites(sugars,amino acids,fatty acids,etc.).However,the mechanism of action of nano-TiO2 on photosynthesis and related metabolic pathways still require further investigated.In this study,we targeted Oryza sativa L-7 to investigate the changes of the key processes of photosynthesis,metabolic pathways and metabolites,based on chlorophyll fluorescence technology and metabolomics,which attempted to explore the hormesis of nano-TiO2 on rice growth from perspective of the energy accumulation.Main results are as follows(1)Nano-TiO2(0.1-100 mg/L)improved the utilization rate of light energy and reduced thermal energy dissipation of rice.Under the exposure of 0.1-100 mg/L nano-TiO2,the photochemical quantum efficiency Y(?)increased by 7.8±3.3%on average,indicating the rise of the utilization rate of light energy in photosystem ?;non-photochemical quenching NPQ decreased by 17.6±5.9%on average,indicating the decline of thermal energy dissipation.The contents of chlorophyll a,chlorophyll b,and total chlorophyll were all significantly increased by>100%,>50%,and 90%under the nano-TiO2 concentrations of 0.1-400 mg/L,indicating that the photosynthetic capacity of rice was improved.Meanwhile,nano-TiO2 could increase the contribution rate of ATP in photosynthesis,with the maximum contribution rate of 20.6%(2)Nano-TiO2(0.1-100 mg/L)induced the increased energy accumulation and reduced consumption in rice,resulting in the rise of rice biomass by more than 30%The disturbance of metabolites and metabolic pathways in leaves is more sensitive to nano-TiO2han that of roots.Large number of metabolites were enriched in fructose and mannose metabolism,starch and sucrose metabolism,and galactose metabolism which related to photosynthesis,were significantly enriched in leaves(enrichment factor>15).And the content of D-fructose,D-galactose,D-talose,and other monosaccharides significantly decreased(>18%),while the contents of D-cellobiose,D-lactose and other polysaccharides significantly increased(>30%),citric acid and malic acid participated in the citric acid cycle(TCA cycle)decreased by 11.3-21.9%and 6.2-25.6%respectively,thereby promoted the energy accumulation.