The Impacts Of Iron Oxide Nanoparticles On The Correction Of Iron-deficit Chlorosis Of Citrus Seedlings

Iron is essential for plant growth,and iron deficiency may cause chlorosis in plant leaves and damage plant growth.Citrus has very high nutritional value and medicinal value,however,which is prone to iron deficiency and appears chlorosis symptoms,leads to the decrease of yield and quality.Compared to traditional iron fertilizer,iron oxide nanoparticles??-Fe2O3 NPs?have several new features such as strong adsorption,slow release effect and penetrability,etc.Therefore,?-Fe2O3 NPs have the potential to provide iron to citrus plants,and promote the growth of plants.This study comprehensively compared and analyzed the physiological and molecular changes of Citrus maxima plants as affected by 20,50 and 100 mg/L of?-Fe₂O₃ NPs and Fe³⁺via root and foliar applications,thus evaluating the improvement of chlorosis of?-Fe2O3 NPs on citrus plants.1.Uptake,translocation and the physiological impact of?-Fe₂O₃ NPs on Citrus maxima plants via root application?-Fe₂O₃ NPs could enter plant roots but no translocation from roots to shoots was observed.20 mg/L?-Fe₂O₃ NPs had no impact on plant growth.50 mg/L?-Fe₂O₃NPs significantly enhanced chlorophyll content by 23.2%and root activity by 23.8%as compared with control.However,100 mg/L?-Fe₂O₃ NPs notably increased MDA?malonaldehyde?formation,decreased chlorophyll content and root activity.Although Fe³⁺ions could be used by plants and promoted the synthesis of chlorophyll,they appeared to be more toxic than?-Fe₂O₃ NPs.RT-PCR analysis showed that?-Fe₂O₃NPs had no impact on AHA gene expression.50 mg/L?-Fe₂O₃ NPs and Fe³⁺significantly increased expression levels of FRO2 gene and correspondingly had a higher ferric reductase activity compared to both control and Fe?II?-EDTA exposure.Relative levels of Nramp3 gene expression exposed to?-Fe₂O₃ NPs and Fe³⁺were significantly lower than control,indicating that all?-Fe₂O₃ NPs and Fe³⁺treatments could supply iron to Citrus maxima seedlings.2.Interaction of?-Fe₂O₃ NPs with Citrus maxima leaves and the corresponding physiological effects via foliar application?-Fe₂O₃ NPs and Fe³⁺exposure via foliar spray had an inconsequential effect on plant growth.In the shoots,20 and 50 mg/L?-Fe2O3 NPs did not induce oxidative stress while 100 mg/L?-Fe2O3 NPs did initially but dealt with it by plant defense system.Furthermore,there was a positive correlation between the dosages of?-Fe₂O₃NPs and Fe³⁺and iron accumulation in shoots.However,the accumulated iron in shoots was not translocated down to roots.We observed down-regulation of FRO2and Nramp3 gene expression exposed to?-Fe2O3 NPs treatments,suggesting that plants were in iron-replete status.Although 100 mg/L?-Fe₂O₃ NPs and 20-100 mg/L Fe³⁺led to higher wax content,genes associated with wax formation?WIN1?and transport?ABCG12?were downregulated or unchanged compared to the control,indicating that the biosynthesis and transport of wax is a collaborative and multigene controlled process.Overall,?-Fe₂O₃ NPs showed significantly various impacts on Citrus maxima plants by root application and foliar spray.The impacts of root applied?-Fe₂O₃ NPs on plant growth was in correlation with the concentrations of NPs.In this situation,?-Fe₂O₃ NPs at proper concentration could effectively improve iron-deficit chlorosis of Citrus maxima plants.On the other hand,foliar sprayed?-Fe2O3 NPs had no obvious impacts on plant growth,but?-Fe2O3 NPs can reduce nutrient loss due to their the strong adsorption ability.In addition,no upward translocation of root applied?-Fe₂O₃ NPs and no downward transport of foliar sprayed?-Fe₂O₃ NPs was observed.Therefore,a combination of both application methods may improve the effectiveness of iron fertilization and effectively improve iron-deficit chlorosis in agricultural production.This study will lay the foundation for the future applications of nano-metric additives in agriculture.