Effects Of Different Concentration Of Boron Fertilizer On Growth And Physiological Characteristics Of Apple Rootstock And Screening Of Boron Transporter Gene Family

Boron is one of the essential trace elements in plants and plays an important role in the growth and development of plants.Apples are sensitive to boron nutrition,especially in the Loess Plateau region,which has a relatively narrow range of adaptation to the concentration of boron,and boron deficiency or boron toxicity will adversely affect plant growth.Although boron has a significant impact on the economic value of crops,the uptake and transport of boron is unclear.In this experiment,apple tissue culture seedling M26 was used as the test material,and cultured in nutrient solution.Four Boron（Boron,B）levels were set,including no Boron(B0,0mg.L^-1),low Boron(B5,5mg.L^-1),suitable Boron(CK,15mg.L^-1)and high Boron(B50,50mg.L^-1),to explore the growth and physiological characteristics of apple seedlings under stress treatment.It is of great significance to further study and analyze the response mechanism of apple to boron stress to improve its stress resistance,promote agricultural efficiency and increase farmers’income.This paper also identified the bioinformation related to the members of the aquaporin（MIP）family,and determined the expression pattern of MIP gene in different tissues and at different concentrations by real-time quantitative PCR.The main results of this study are divided into the following parts:Under the treatment of boron deficiency（B0）and boron toxicity（B50）,the root growth of apple was inhibited,the root activity was significantly reduced,and the young leaves in the shoots were cupped and curled,and the contents of chlorophyll a,chlorophyll b and carotenoids in the leaves were decreased.The relative conductivity and malondialdehyde content in boron deficiency（B0）treatment were higher than those in the control group for most periods,and those in boron toxicity（B50）treatment were significantly higher than those in the control group,while low boron（B5）treatment had no significant changes.Under boron deficiency and boron toxicity,the activities of SOD and POD were significantly higher than those of the control.The content of endogenous boron under high boron treatment was significantly higher than that of the control.The major intrinsic protein（MIP）has multiple functions in plant growth,development and stress response.Therefore,genome-wide identification and identification of the MIP gene superfamily of a pple were carried out,and 43 MdMIP genes were identified.According to their homology,they were divided into five subfamilies:PIP,NIP,TIP,SIP and XIP.Phylogenetic analysis and composition analysis showed that there were similar gene structures and conserved motifs among the MdMIP subfamilies,while there were significant differences among different subfamilies.MIP is made up of highly conserved monomers that exist in the cell membrane as tetramers.The selectivity of transport is guided by two types of contraction on the channel:the first contraction on rings B and E consisting of two highly conserved（NPA）motifs,and the second contraction known as ar/R selective filtering.MdMIP gene promoter also contains a variety of cis-acting elements,which are involved in the growth and development of apple.Chromosome mapping revealed that 43MIP genes were distributed on 17 chromosomes.Protein interaction network analysis revealed associations between 42 MdMIP and 22 At MIP,with multiple pairs of genes having similar functions.The expression profile of MdMIP gene by real-time quantitative PCR analysis showed that the expression patterns of MdMIP gene in different tissues were different in response to boron stress.Under boron deficiency treatment,MdNIP5-1 gene responded to boron deficiency stress in roots and leaves,especially in roots,suggesting that this gene was involved in the uptake of boron in apples.The expression levels of MdNIP2-1 and MdNIP2-2 genes were significantly higher than those of the control group at 6h of treatment with boron deficiency in the root.With the extension of stress time,the expression levels of MdNIP2-1 and MdNIP2-2 genes showed a trend from high to low,suggesting that these two genes may be involved in the transport of boron in the shoot of apple and to the growth site.The expression of MdNIP6-1 in the leaves was significantly higher than that of the control group,which also proved that NIP6-1 had the function of preferentially transporting boron to the above ground.The expression of MdPIP1-3 and MdPIP1-4 genes was significantly up-regulated in the root and then showed a downward trend,which played a key role in the response of apples to boron stress.MdPIP2-7 gene was up-regulated in both roots and leaves.MdNIP2-1 and MdNIP2-2 genes were up-regulated in roots under boron toxicity;MdPIP2-7 was highly expressed in leaves,which improved the tolerance of plants to boron stress.In summary,under boron stress,the effects of growth and physiological characteristics during the development of apple were studied.Through bioinformatics analysis,the members of the MIP gene family in apple were identified to preliminarily explore its functional characteristics,providing a basis for further research on more functions of apple.