Regulation Mechanism Of Biomass Carbon Dots On Plant Photosynthesis And Quality

As the global population continues to grow,so does the pressure on food supplies.Since the Green Revolution,a large number of chemical fertilizers and pesticides have been used to increase crop yields and quality,but their overall utilization efficiency is low（<50%）and there are serious environmental risks.With the rapid development of nanotechnology,artificial nanomaterials have shown great application potential in regulating crop yield,quality and resistance,reducing resource input,and reducing agricultural environmental pollution.As a kind of carbon-based nanomaterials,carbon dots（CDs）can be used in fluorescence imaging,biomedicine and many other fields due to their good fluorescence characteristics,biocompatibility and low toxicity.Biomass carbon dots（B-CDs）have attracted much attention because of their wide range of sources,convenient synthesis methods,low cost and environmental friendliness.However,the specific mechanism of B-CDs in regulating crop photosynthetic process and quality is still unclear.Therefore,three kinds of B-CDs were synthesized using soybean,walnut and seaweed as raw materials,in order to explore the optimal synthesis conditions of B-CDs and their internal mechanism to regulate plant photosynthetic process and quality.The main conclusions are as follows:（1）Optimize the synthesis conditions of B-CDs by changing the reaction conditions（reaction time,reaction temperature,raw material dosage and water consumption）in the hydrothermal synthesis process.The results showed that the yield of B-CDs in the hydrothermal reaction at 180°C for 6 h reached the maximum（50%）when using soybean as raw material.Transmission electron microscopy（TEM）characterization showed that B-CDs were between 5-20 nm in size and lattice spacing at approximately 0.23-0.25 nm.Surface functional group analysis showed that B-CDs contained a large number of hydrophilic groups such as·NH₂、·COOH and·OH,so they had good biocompatibility.B-CDs showed obvious blue fluorescence under ultraviolet irradiation,and the fluorescence intensity was excitation wavelength-dependent,reaching a peak at 343 nm.The B-CDs synthesized from different raw materials（Soy-CDs,Wal-CDs and Lay-CDs）also had advantages in different element content,Soy-CDs were rich in Mg(3539.34 mg·kg^-1),Wal-CDs were rich in Cu(15.96 mg·kg^-1),and Lay-CDs were rich in Fe(361.95 mg·kg^-1).（2）It is clarified that B-CDs can be absorbed and transported by plant leaves without damaging the morphological structure of chloroplasts.B-CDs of 10 mg·L^?1significantly promoted the growth of green cabbage and were better than those treated with citric acid CDs.In addition,because the three B-CDs are rich in different elements（Mg,Cu and Fe）that can act on different stages of the photosynthetic process,Mg in Soy-CDs can significantly increase the chlorophyll content of green vegetables（103.6%）,and Cu in Wal-CDs can significantly increase the electron transport rate（112.1%）.Lay-CDs significantly increased ferredoxin（Fd）synthesis due to high Fe content（85.9%）.At the same time,B-CDs can also regulate Ru Bis CO enzyme activity,carbohydrate and increase the expression level of photosynthesis-related genes（Bna0391450 and Bna0280620）to jointly increase the photosynthesis intensity of plants.The results of DCPIP attenuation rate and absorption spectroscopy of plant chloroplasts and Soy-CDs/chloroplast complexes showed that Soy-CDs could convert ultraviolet light into light that could be absorbed and utilized by plants,improve the light capture capacity of plant chloroplasts,and enhance photosynthesis.The above results show that in addition to regulating the light capture ability of leaves,B-CDs can also regulate key pigments,key enzymes and electron transport in the photosynthetic process,thereby enhancing the photosynthetic capacity of crops and promoting nutrient synthesis.In addition,B-CDs doped with different elements（Mg,Cu and Fe）can also alleviate the effects of deficiency（Mg,Cu and Fe）on plant growth and maintain normal plant growth.（3）The mechanism of Soy-CDs(10 mg·L^·1)to improve crop quality and its regulation was discovered.Compared with the control,Soy-CDs(10 mg·L^·1)significantly promoted grain development,which in turn increased maize yield.At the same time,the expression levels of genes encoding starch synthase（AGPL-3,SS2b-2 and BE-3）in maize increased significantly（142.0%,214.2%and 52.4%）,thereby increasing the starch content（17.2%）in the grain.In addition,the expression of coding genes affecting aspartate kinase（AK）and dihydrodipicinic acid synthase（DHPS）synthesis（AK and DHPSrt）was also significantly up-regulated（63.0%and 79.5%）,thereby promoting the synthesis of amino acids such as lysine and leucine in corn kernels.The non-targeted metabolic results also further proved that Soy-CDs can increase the abundance of quality-related beneficial metabolites（asparagine,niacinamide,glutathione,etc.）in maize kernels,and ultimately improve the nutritional quality of maize.In conclusion,the low-cost synthesis of B-CDs is realized by controlling the reaction conditions to regulate the yield of B-CDs,which proves that B-CDs can enhance the light capture ability of plant chloroplasts,improve the net photosynthetic rate,and promote photosynthesis.It was also proved that B-CDs could up regulate the expression level of relevant coding genes in maize with important nutritional indicators,increase the abundance of beneficial metabolites,and ultimately improve crop quality.B-CDs not only meet the needs of large-scale synthesis of nanomaterials,but also have the function of improving photosynthesis and promoting quality,which means that B-CDs as an emerging nanofertilizer can be widely used in plants,providing broader prospects for the development of nanoagriculture.