Response Of Myo-Inositol To Boron Deficiency And Its Effect On Cell Wall Structure And Energy Metabolism Of Trifoliate Orange

Boron is an essential microelement for the normal growth and development of citrus.Most of the citrus growing areas in China have low boron content in the soil.The boron deficiency of citrus is common,and boron deficiency has severely restricted the yield and output of citrus in China.Citrus is grafted and propagated by rootstock and scion,mainly relying on rootstock roots to absorb water and nutrients from soil.Trifoliate orange [Poncirus trifoliata(L.)Raf.] is a well-known main citrus rootstock in China and is very sensitive to B deficiency.As a precursor of a large class of compounds,myo-inositol is an important compound for cell metabolism and plant growth and development.Its oxidation pathway plays an important role in hexose / pentose metabolism,cell wall pectin and hemicellulose formation,and starch synthesis.In the early stage of this research group,we studied inositol was abundant in navel orange leaves,and its content changed significantly after boron deficiency stress,which was closely related to the degree of boron deficiency,but its response mechanism to boron deficiency was not clear.Boron is the structural component of cell wall.Boron deficiency leads to the disorder of cell wall composition and structure.Inositol is an important precursor of cell wall synthesis.Is the change of inositol content after boron deficiency one of the reasons for the change of cell wall structure composition?Based on the above scientific problems,young plants of trifoliate orange rootstock sensitive to boron deficiency were selected to grown in a nutrient solution,measuring the dynamic changes of inositol content in leaves and roots and the expression of enzyme genes related to inositol metabolism under boron deficiency.To clarify the response mechanism of inositol to boron deficiency;Further exogenous spraying of inositol treatment,using SEM(Scanning electron microscope),XRD(X-ray diffraction),XPS(X-ray photoelectron spectroscopy)and FITR(Fourier-transform infrared spectroscopy)to characterize the changes in cell wall structure and composition,using LC-MS target metabolomics technology to determine the effect of exogenous inositol on leaves energy metabolism,In order to deeply understand the response of inositol to boron deficiency stress and its regulatory role in cell wall metabolism and energy metabolism.It provides a theoretical basis for further research on the molecular mechanism of the regulation of boron deficiency in navel oranges and the application of corresponding cultivation measures on boron-deficient soils.The main results are as follows:1.With the lengthen of boron deficiency time,the boron content in leaves and roots decreased significantly compared with control.And the growth of trifoliate orange seedlings stopped after boron deficiency 1 month,but there was no significant difference in dry weight in leaves,stem and roots.However,the dry weight of trifoliate orange seedlings decreased significantly of boron deficiency 1 month,shows that boron deficiency inhibits the Trifoliate orange growth and development.2.Boron deficiency significantly increased the inositol content in the roots of young seedlings,but there was no significant difference in leaves.Compared with control,the expression of boron-deficient MIPS(myo-Inositol phosphatesynthase)was significantly up-regulated in roots and leaves;IMP(Inositol monophosphatase)was down-regulated in leaves under B-deficient solution for 1 month,but no changes in leaves and roots for 2 month;MIOX1 was down-regulated in leaves and roots under B-deficient solution for 1 month and 2 month;MIOX2was down-regulated in leaves under B-deficient solution for 1 month,up-regulated in roots under boron deficiency for 2 month,but no changes in roots under B-deficient solution for 1 month and leaves under B-deficient solution for 2 month.There was no significant difference in the expression of MIOX3 in the leaves of B-deficient solution for 1 month,but the expression was up-regulated in the leaves of B-deficient solution for 2 month and down regulated in the roots for1 month and 2 month.The expression of GPP was up-regulated in both leaves and roots of B-deficient solution for 2 month,and the difference of expression levels of related enzyme genes further proved the regulation of MIOX(myo-Inositol oxygenase)on inositol metabolism.3.Compared with control,the cell wall structure and composition of the leaves and roots were significantly changed after boron deficiency treatment.After boron deficiency,The SEM observed that the surface of the cell wall was rougher than the control.When B-deficient solution for 2 month,the cell wall would have the harden phenomenon,indicating that the cell wall structure was destroyed.FTIR,XRD and XPS spectra showed that the content of cellulose increased significantly and the protein structure in the cell wall was destroyed.4.Exogenous spraying of inositol,the each part biomass of trifoliate orange seedlings no significant differences but have decreased tendency after exogenous spraying of inositol.The biomass of the whole trifoliate orange seedlings decreased significantly Indicating that its growth was inhibited under the action of exogenous inositol.5.Exogenous spraying of inositol,the expression of MIPS in leaves and roots was significantly down-regulated;MIOX1,MIOX2,MIOX3 were significantly up-regulated;IMP was up-regulated in leaves,but there was no significant difference in roots;GPP was not significantly different from the control.Under the action of exogenous inositol,the synthesis of inositol was reduced and the oxidative decomposition was increased by plant autoregulation.6.Exogenous spraying of inositol,the results of FTIR,X-RD,XPS indicated that the cell wall structure and components of the leaves and roots of trifoliate orange seedlings changed significantly,The increase of inositol content affects the relative carbon content of cellulose,glycoprotein and fatty acid in cell wall.7.Exogenous spraying of inositol,the contents of phosphate-6-fructose,D-glucose-6-phosphate,3-phosphate-D-glycer,phosphoenolpyruvate,pyruvate oxaloacetate and fumarate decreased significantly compared with the control.Exogenous spraying inositol inhibits the process of energy metabolism and turns to the direction of cell wall metabolism,which leads to the disorder of cell wall structure and inhibits the growth of trifoliate orange seedlings.