Function Of Phosphatidylcholine On Improving Salt Tolerance And Maintaining Phospholipid Homeostasis In Peach Seedlings

Peach has poor salt tolerance,and soil salinization is one of the main constraints affecting peach growth and productivity.Salt stress inhibits peach growth and reduces its yield,which limits the sustainable development of fruit industry such as peach.Phosphatidylcholine(PC)is an important cell membrane component,the most important phospholipids in eukaryotes,and is essential for the maintenance of cell structure and membrane structure stability.In addition to being the main phospholipids in most eukaryotic cell membranes,PC is also an important precursor of lipid signaling,or a ligand for regulatory proteins,whose breakdown products phosphatidic acid(PA)and choline respond positively to salt stress.However,the effect of PC on peach in response to salt stress and its regulatory physiological mechanism remain unclear.Therefore,in this study,the physiological effects of PC on alleviating salt stress in peach seedlings and Arabidopsis thaliana were studied,and the effects of PC on phospholipid homeostasis in peach roots under salt stress were explored by means of lipid metabolomics.Further,transcriptomics and molecular biology techniques were used to elucidate the regulatory mechanism of PC’s enhancement of salt resistance in peach seedlings roots.The main results are as follows:1.Exogenous PC significantly improved the tolerance of peach seedlings(Prunus persica (L.)Batsch.)to salt stress and reduced the damage caused by salt stress,among which 200mg/L PC had the best effect.Compared with salt treatment,exogenous PC increased stomatal area of peach seedlings leaves by 37.4%and relative chlorophyll content of peach seedlings by 20.9%under salt stress,and maintained normal photosynthesis of leaves.In addition,the root growth of peach seedlings was inhibited and the root growth decreased under salt stress.Compared with salt treatment,exogenous PC can reduce the inhibition of Na Cl on the growth of peach root system and increase the growth amount of root system under salt stress.2.Under salt stress,PC could activate the activity of antioxidant protective enzyme,and ROS content in leaves and roots decreased.Compared with salt treatment,the contents of osmotic regulation substances proline,glycine betaine and soluble sugar in peach seedling root increased by 54.8%,92.7%and 72.3%,respectively,under salt stress,which decreased the osmotic stress caused by salt.MDA content and electrolyte exosmosis rate of peach seedling root decreased 48.4%and 29.7%,respectively,and lipid peroxidation damage of cell membrane was reduced.3.Transmission electron microscopy(TEM)was used to observe the integrity of cell morphology and cell membrane structure of peach root system.It was found that under normal conditions,the root cell morphology was rounded and full,with the best integrity,while under salt treatment,the root cell morphology was the worst.The morphological integrity of root cells in PC treatment was higher than that in salt treatment.Salt treatment damaged the cell membrane structure,the phospholipid bilayer structure,the cell fluid leakage,and the physiological function of root cells.The salt treatment with PC can maintain the integrity of cell morphology and membrane phospholipid bilayer structure,and ensure the normal physiological function of cells.4.Exogenous addition of PC promoted the activity of phospholipase D(PLD)in cells,and the increase of PLD activity promoted the decomposition of phospholipid and the content of phospholipic acid(PA).Compared with salt treatment,PLD activity and PA content increased 295.4%and 206.1%,respectively,in peach root lines supplemented with 200mg/L PC under salt stress.5.Lipid metabolomics analysis showed that exogenous application of PC increased the total phospholipid content in peach roots under normal conditions and salt stress.Compared with CK,the total phospholipid content decreased under Na Cl treatment,indicating that the plants responded to salt stress through the decomposition of intracellular lipids,while exogenous PC supplementation increased the content of intracellular phospholipid,thus enhancing the resistance of peach roots to salt stress.Compared with Na Cl treatment,The accumulation of Lipid metabolite PC(Lipid B-N-0102,Lipid B-N-0103,lipid B-N-0124)and PA(Lipid B-N-0484,lipid B-N-0499)is significantly increased under Na Cl+PC treatment.6.Transcriptomic analysis indicated that lipid metabolism was an important metabolic pathway in peach root system under salt stress.Through functional annotation and enrichment analysis of transcriptomic differentially expressed genes,we found that MAPK signaling pathway was closely related to resistance to salt stress in peach trees.Through RNA-Seq analysis and real-time quantitative fluorescence PCR(qRT-PCR),we found that PpMPK6 expression in peach roots was significantly up-regulated under salt stress.7.Under salt stress,the aboveground growth of OE-PpMPK6 Arabidopsis Thaliana was better than that of WT and KO-AtMPK6,and the aboveground growth of KO-AtMPK6 was the worst.Under normal conditions,the root length of OE-PpMPK6 was slightly higher than that of WT and KO-AtMPK6,while the root growth of KO-AtMPK6 was severely inhibited under salt stress,and the resistance of KO-AtMPK6 to salt stress was significantly reduced.8.In addition,we detected the Na~+content in Arabidopsis Thaliana roots under salt stress,and found that the Na~+content in OE-PpMPK6 roots was significantly lower than that in WT and KO-AtMPK6 strains,and the Na~+content in the roots of KO-AtMPK6 strains was at a higher level.This indicated that exogenous PC might regulate PpMPK6 through PA to reduce the content of Na~+in plant roots,thus alleviating the root damage caused by NaCl.