Underlying Mechanism And Application Of Nanocellulose-iron Chelation For Remediation Of Pear Iron Deficiency Chlorosis

In this study,Pyrus betulaefolia seedlings were used to explore the feasibility of nanocellulose-iron chelate（NCFe）application in pear production and possible mechanism of NCFe iron deficiency chlorosis（IDC）control.We used transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）,and Fourier transform infrared spectroscopy（FTIR）to characterize nanocellulose（NC）and NCFe.By measuring the SPAD value,the active iron content from leaves treated with different charge ratios of NCFe,the best charge ratio for remediation IDC was determined.The photosynthesis parameters,chlorophyll content,the relative expression of ferritin gene（Pb FER）,and pectin methylesterase gene（Pb PME）were measured to systematically explore the mechanism of NCFe for IDC control.Different concentrations of mineralized water were used to prepare NCFe and foliar applied to IDC leaves to investigate the effects of NCFe on the nutrient element contents,ferritin gene expression levels.This finding will provide a theoretical support for future application of NCFe.1.Physical properties of NC: The concentration of NC aqueous suspension prepared by sulfuric acid hydrolysis method was 0.00851 g·m L^-1,the net charge density was 0.2135 mmol·g-1,the particle size and the zeta potential were 84.3 ± 0.2nm and-47.3 ± 1.7 m V respectively.NC particles with crystallinity of 63.12%showed rod-like whiskers examined by TEM.In NC-Fe combination,Fe（II）was attached on the surface of NC determined by XPS.The results of XRD detection showed that NCFe reduced the crystallinity of NC,the spectra of FTIR showed that the relative intensity of the peaks and the change of hydrogen bonds after chelation affecting the spatial structure of NC.2.The charge ratio of NC:Fe 1:300,1:3000,1:30000 were chosen to prepare NCFe.After spraying72 h,the phenotype of leaves showed that NCFe prepared under the charge ratio of 1:3000 was the best formulation to remediate IDC.SPAD value of leaves treated with NCFe was higher than that of Fe-EDTA and Fe SO₄.NCFe formulated by the charge ratio of 1:3000 has maximum value of SPAD;the active iron content of leaves treated with NC:Fe 1:3000 was higher than that of 1:300,1:30000,and also significantly higher than that of Fe-EDTA and Fe SO₄.3.Compared with Fe SO₄ treatment and CK,the content of chlorophyll a from the NCFe treatment was significantly increased by 39.3% and 112.5% respectively,the content of chlorophyll b was significantly increased by 62.5% and 116.7%,the total chlorophyll content was significantly increased by 42.3% and 113.5%respectively;and the net photosynthetic rate was significantly increased by 40.4% and121.7% respectively.Based on the energy spectrum analysis from scanning electron microscope（SEM）images of the leaf surface,NCFe promoted the absorption of Fe when spraying on the leaf after 2 h treatment;indicating that NCFe could be able to enhance the net photosynthetic rate of the leaves.The results of q PCR showed that NCFe significantly promoted the relative expression levels of ferritin genes（Pb FER1,Pb FER2,Pb FER3,Pb FER4）which was 1.5,1.6,and 1.7 times as much as that of Fe SO4 treatment,respectively,and 3.6,4.2,and 4.0 times as much as that of CK.The relative expression levels of pectin methylesterase genes（Pb PME1,Pb PME3,Pb PME4）of CK were 2.7,1.8,and 7.3 times as much as that of the NCFe treatment,and 1.4,1.8,and 1.7 times that of Fe SO₄ treatment,respectively.4.Mineralized water with different concentrations of 750 mg·L^-1,1500 mg·L^-1,3000 mg·L^-1 were used to prepare NCFe suspension.The particle size and zeta potential of 3000 mg·L^-1 of mineralized water formulated NCFe were increased by670.7% and 26.3% respectively compared with 1500 mg·L^-1 of mineralization,and increased 888.0% and 59.6% respectively compared with 750 mg·L^-1 of mineralization,respectively.With increase of concentration of mineralized water in NCFe formulation,the content of active iron in treatment by NCFe prepared with 750mg·L^-1 of mineralization was decreased by 16% comparing with 1500 mg·L^-1 of mineralization.It was decreased 34.4% when formulated with 3000 mg·L^-1 of mineralization;there was no significantly difference between formulation with 3000mg·L^-1 of mineralization and Fe SO₄.Total calcium and total magnesium content were decreased when treated with NCFe formulated with 3000 mg·L^-1 of mineralization,but the content of total sodium was increased.The relative expression of ferritin gene Fer1 in leaves was decreased significantly.Among the treatments,the 750 mg·L^-1 of mineralization of the treatment was 1.5 times than that of 1500 mg·L^-1 and 2.5 times than that of 3000 mg·L^-1 of mineralization.Therefore,the metal ions could destroy the chelation of NC to Fe and affect the efficacy of NCFe in IDC control.