Effects Of ABA On Salt Secretion And Salt Tolerance Of Salt Glands Of Reaumuria Trigyna

Salt glands,special epidermal cells of secretohalophyte,improve the survival ability of plants by excreting excess salt.Reaumuria trigyna,belongs to the Reaumuria of the family Tamarieaceae,is one of the tertiary Tethys relict plants.It is a kind of xerophytic halophyte shrub distributed in East Alashan West Ordos,and the unique salt gland structure is essential for its survival in saline environments.In this study,to investigate the effect of ABA on salt secretion of salt gland and salt tolerance of plant,the Na⁺and K⁺secretion rate of salt gland as well as the physiological and biochemical indices was measured by NMT?Non-Invasive Micro-test Technique?in Reaumuria trigyna treated by ABA.Based on the fact that vesicular transport is involved in salt secretion in the salt glands of Reaumuria trigyna,the vesicular transport related gene RtVAMP2-2 was cloned here.The main results are as follows:1.Abscisic acid?ABA?was used to treat Reaumuria trigyna under salt stress,and the results showed that,ABA could promote the excretion of Na⁺from a single salt gland while relieving the loss of K⁺,which increase the Na⁺/K⁺significantly in the salt gland secretion.It can maintain a lower Na⁺/K⁺ratio in plants by reducing the content of Na⁺as well as increasing the content of K⁺in leaves.In addition,the activity of ACP increased,which is a vesicle transport marker.qRT-PCR results revealed that,the expression levels of Na⁺,K⁺ion transport related genes RtSOS1,RtHKT and vesicle transport related genes RtVAMP2-2 and RtVAMP1-2 were significantly higher than those of salt stress and control group.Nevertheless,these changes were restored after adding ABA inhibitor sodium tungstate.It is speculated that ABA can improve the salt tolerance of Reaumuria trigyna by regulating the secretion of salt glands.2.Abscisic acid?ABA?was used to treat the Reaumuria trigyna under salt stress.It was found that the fresh weight,dry weight,chlorophyll content,water content,degree of succulence,PRO content,SOD and POD activities of plants were significantly higher while MDA and relative conductivity were lower than those of salt treatment.It revealed that,the expression of antioxidant-related genes RtAPX,RtGRX,and RtSOD were induced by ABA.And while treated by sodium tungstate,the above changes caused by ABA treatment were restored.All of the above results demonstrated that,ABA can improve the salt tolerance of Reaumuria trigyna by controlling oxidation balance.3.The vesicle transport related gene RtVAMP2-2 of Reaumuria trigyna contains a 1076 bp ORF.It encodes a protein of 357 amino acids with a molecular weight of40.381 kDa.And its theoretical isoelectric point is 6.01,which belongs to hydrophilic protein without signal peptide.There is a strong transmembrane helix at the C-terminal.Amino acid sequence alignment analysis showed that RtVAMP2-2contained two conserved domains,the main sperm protein?MSP?domain and the SCS2 domain.Phylogenetic tree results showed that RtVAMP2-2 has the closest relationship with capsicum protein which clustered together,but has distant relationship with Populus tomentosa and mulberry protein.And the subcellular localization revealed that the protein was located on the plasma membrane.Other than this,The expression pattern analysis proved that RtVAMP2-2 gene was expressed in the roots,stems and leaves of Reaumuria trigyna,and the highest expression was detected in the stems.Meanwhile,the expression of RtVAMP2-2 gene could be induced by NaCl,exogenous ABA treatment,H₂O₂,4?and CaCl₂.4.The RtVAMP2-2 eukaryotic expression vector was constructed,and which was transformed into Arabidopsis thaliana.After treated with different concentration gradients of NaCl,the root length,fresh weight and chlorophyll content of transgenic lines were significantly lower than those of WT.DAB and NBT staining showed that,more reactive oxygen was accumulated in leaves of transgenic plants than that of wild-type under salt stress,which resulted in the transgenic Arabidopsis thaliana being more sensitive to salt stress.Taken together,the transgenic lines of RtVAMP2-2gene are more sensitive to salt stress,and as the increase of salt concentration,the sensitivity increased.Therefore,RtVAMP2-2 may act as a negative regulator to regulate the response of plants to salt stress.