Study On Metal Oxide Nanozymes And Fluorescence Carbon Dots Enhance Crop Salt Tolerance And Photosynthesis

With rapid population growth,improving the yield of crops is one of the important initiative to secure food supply.Salinity issue is an environmental factor affecting crop yield,which severely restricts the productivity of agricultural output.However,the existing approach to alleviating salt stress have inevitable limitations such as long period and waste of resources.Therefore,it is important to find a fast and low-cost method to reduce the loss caused by salt stress to improve the productivity of farmland.Our country is a big cotton-planting place with the main cotton area located in Xinjiang.Unfortunately,the salinization of cultivated land is serious in Xinjiang.As we all know,the cotton production in our country is seriously restricted by salt stress.To address the big issue,nanobiotechnology has been adopted in improving plant stress tolerance.Nanomaterials with mimicked enzyme activities are defined as nanozymes.Up to now,massive studies have been devoted to improve plants salt tolerance by using nanozymes.However,there are few reports on enhance cotton salt tolerance and crop green light use efficiency by nanobiotechnology.Based on the above research purposes,three specific research items designed are as follows:（1）explore the applicability of the nanozymes on cotton by using the widely reported ceria nanoparticles and explore its biological effects;（2）design and optimize Mn₃O₄ nanozymes to explore the mechanisms underlying their ability to improve salt tolerance in cotton;（3）enhance photosynthesis in rapeseed by using GR-CDs（Green to red conversion carbon dots）which can convert green light to red light.The conclusions of this thesis are as follows:1.Poly acrylic acid coated nanoceria（PNC）can effectively enhance cotton salt tolerance.Under salt stress,cotton treated with PNC had a better phenotype,higher chlorophyll content（by 68%）,biomass accumulation（68%increase）,and better photosynthetic performance in relative to the control group（38%increase）.Meanwhile,PNC also improved ROS scavenging ability of cotton leaves.Under salt stress,ROS and MDA contents in PNC treated leaves were decreased by 79%and 44%respectively compared with control groups.Further results revealed that PNC treated cotton leaves had a higher K⁺content（84%increase）,lower Na⁺content（63%decrease）,and higher K⁺/Na⁺ratio.Interestingly,the Na⁺content of vacuoles was also lower in PNC treated leaves.The results of q PCR showed that PNC enhanced the ability of xylem Na⁺loading in cotton and reduced loss of K⁺,thus improving the salt tolerance of cotton.2.Six types of manganese tetroxide（Mn₃O₄）nanozymes were synthesized and characterized.The mechanisms underlying the ability of Mn₃O₄ nanozymes to improve salt tolerance in cotton were revealed from the perspectives of plant biology and nanoscience.In this study,three Mn₃O₄ nanozymes（named MO1,PMO1,and EMO1）based on Mn（Ac）₂ were synthesized,but they did not enhance cotton salt tolerance at 200mg L^-1 once applied.Therefore,Mn₃O₄ nanozymes（named MO2,PMO2,and EMO2）based on Mn SO₄ were further designed and synthesized.After cotton was treated with MO2,PMO2,and EMO2,it was found that PMO2 could effectively enhance cotton salt tolerance.Further experiments showed that PMO2 treated cotton leaves had higher fresh weight（64%increase）,better photosynthetic performance（178.6%increase）,lower ROS content(H₂O₂ and O₂^·-had 44.1%and 85.6%decrease,respectively),and better K⁺/Na⁺ratio.This experiment provides a comparative analysis of ROS scavenging by Mn₃O₄nanozymes from the perspective of nanoscience and a mechanistic insight using density functional theory.3.GR-CDs promote rapeseed growth by converting green light to red light.After 12days’growth under green light,the fresh weight of GR-CDs treated plants was significantly higher than no-nanoparticle control group.Determination of photosynthetic parameters and ¹³CO₂ experiments showed that GR-CDs treated plants had better CO₂assimilation rate.Further,after 12 days of growth under white light,GR-CDs treated plants grew better than control plants.Its photosynthesis performance is in consistent with the results under green light.Meanwhile,an experiment set under red and blue light excluded the interference of red or blue light.Long term experiment（48 days）under white light showed higher fresh weight of GR-CDs treated plants.In conclusion,this study provides more examples and theoretical support for the application of nanobiotechnology to enhance plant stress resistance and photosynthetic capacity,which is beneficial to the sustainable development of nano-enabled agriculture.