The Preliminary Mechanism Of The Effect Of Boron And Calcium Deficiency And Exogenous Calcium L-aspartate Nanoparticles On The Root Growth Of Trifoliate Orange

Due to the leaching of rainwater,the deficiency of boron(B)and calcium(Ca)are very serious in the south of China.Both of them are essential nutrients for plant growth and play important roles in maintaining the normal function and structure of cell wall.In recent years,a series of achievements have been made in the study of the correlation between B and Ca.However,the difference of the effect of the interaction between B and Ca on the cell wall of trifoliate rootstock,especially on the cell wall of trifoliate rootstock,has not been reported.Exogenous calcium L-aspartate nanoparticles(Ca(L-asp)-NPs)was widely used in the pharmaceutical industry as a Ca supplement,but whether it could be used as Ca fertilizer for plant growth or not is unknown.In this study,the effects of B and Ca deficiency and exogenous Ca(L-asp)-NPs on the root growth,element content,metabolite composition,cell wall growth,pectin and other parameters of trifoliate rootstock were systematically studied in order to reveal the potential mechanism of B and Ca deficiency and the effect of exogenous Ca(L-asp)-NPs on the growth of trifoliate rootstock provide theoretical basis.The results were as follows:(1)-B+Ca and +B-Ca treatments increased root length,decreased root surface area and root volume.The results of factor analysis showed that the proportion of middle root might be the main root type of B and Ca absorption.Moreover,the treatment of-B+Ca and +B-Ca seriously hindered the normal growth of the root of trifoliate rootstock,led to the decrease of biomass,promoted the absorption of Ca and B and the transportation to the shoots of trifoliate rootstock,and finally caused the metabolism change of trifoliate rootstock.(2)Lack of B and Ca will lead to the decrease of plant biomass and the inhibition of root growth.Ca deficiency decreased the fresh weight of root,stem and leaves by 47%,50% and 62%,respectively,while B deficiency only reduced the fresh weight of root.Combined with principal component analysis and pearson correlation analysis showed that there were significant differences in root parameters between the treatment of B and Ca deficiency and the control.The results of transmission electron microscopy showed that Ca deficiency reduced the cell wall thickness,while B deficiency increased the cell wall thickness.Combined with X-ray diffraction,Fourier transform infrared spectroscopy,immunohistochemistry(JIM5 and JIM7)and other technologies,it was suggested that the above changes may be due to the different methyl ester degree of pectin and glycoprotein of cell wall.To sum up,B deficiency can promote the formation of low methoxylated pectin,increase the thickness of cell wall,and then affect the morphological development of root system;under the condition of calcium deficiency,the formation of high methoxylated pectin,increase the degradation of cell wall,so as to inhibit the formation of root elongation and branch.(3)Different concentrations of Ca(L-asp)-NPs had significant effects on the growth of trifoliate rootstock under Ca deficiency.With the increase of concentration,the total root length,root volume and root surface area showed a significant downward trend,but the total biomass accumulated the highest in 80 mg/L treatment.With the increase of treatment concentration,the Ca content in root,stem,leaves and chelated pectin increased gradually,and a large number of Ca(L-asp)-NPs were accumulated in the root cell wall.Compared with the control,the content of chelated pectin and alkali solution pectin decreased,the content of water-soluble pectin in 320 mg/L treatment decreased,and the degree of pectin methylation changed.The results showed that 80 mg/L Ca(L-asp)-NPs treatment had the best growth potential,too high or low would have adverse effects,and the adverse effects were caused by the change of pectin distribution in different forms of roots and the degree of pectin methylation.Therefore,the difference between B and Ca deficiency in inhibiting the growth of trifoliate orange was caused by the change of root structure and the change of pectin methyl esterification degree of cell wall.In addition,80 mg/L Ca(L-asp)-NPs treatment can significantly promote the growth of trifoliate rootstock,which is most beneficial to its growth.