Growth,Physiological And Transcriptome Analysis Of Trollius Chinensis Seedlings In Response To Complex Saline-Alkali Stress

Saline-alkali stress affects plant growth and development.Trollius chinensis is a herbaceous medicinal plant with high value in garden applications,but its response mechanism to saline-alkali stress is unclear.In this study,we used Trollius chinensis seedlings as research materials to reveal the influence of saline-alkali stress on Trollius chinensis seedlings from growth,physiological and molecular perspectives,by simulating different levels of complex saline-alkali stress.The results are as follows:（1）The damage index of seedlings did not exceed 50%in all p H treatment groups under low salt(40-80 mmol·L^-1),while seedlings under high salt(120-160 mmol·L^-1)environment had difficulty in growing and had blackened roots.With increasing salinity and alkalinity,the height growth of seedlings continued to decrease,while root/shoot ratio and total biomass showed low promotion and high inhibition,with significant growth inhibition at high salinity(160 mmol·L^-1).（2）Various changes in physiological metabolism occurred in Trollius chinensis seedlings with increasing salinity and alkalinity.The RWC content of seedling leaves decreased and the MDA content increased significantly.The root activity was extremely significantly lower than CK at high salt(160 mmol·L^-1).The chlorophyll content,P_n,T_r and G_s of seedling leaves decreased significantly,with the greatest decrease occurring at high alkalinity（p H 9.85）and high salt(160mmol·L^-1),while the increasing C_i indicated that the photosynthetic inhibition in Trollius chinensis seedlings was non-stomatal factors.The changes in chlorophyll fluorescence parameters suggest an inhibition of PSII functional activity and a disruption of the photochemical structure of the leaves.The increased salinity and alkalinity also stimulated significant increase in osmoregulatory substances,and the antioxidant system was activated to scavenge the increased reactive oxygen species（H₂O₂ and O₂·^-）.While the As A-GSH cycling system was stressed,the activities of APX,DHAR,MDAHR,GR and the antioxidant substances content of As A and GSH were significantly increased under high salt(120-160 mmol·L^-1)to maintain the stability of the antioxidant regulation.In terms of cation balance,the aboveground Na⁺,K⁺,Ca²⁺and Mg²⁺contents of seedlings were greater than those of the belowground,where the belowground was more capable of accumulating Mg²⁺and selective for K⁺and Ca²⁺transport.There was an antagonistic effect between the cation,the Na⁺content increased leading to a decrease in K⁺and Ca²⁺deficit.The cation ratios decreased significantly with increasing salinity and alkalinity,indicating that seedlings became less tolerant.（3）Principal component analyses showed that growth,photosynthetic,O₂·^-and cation ratios and transport could be used as reference indicators of saline-alkali tolerance in Trollius chinensis.A comprehensive analysis of the affiliation function revealed that the saline-alkali tolerance of Trollius chinensis seedlings was low alkalinity（p H 7.87）>medium alkalinity（p H 8.71）>high alkalinity（p H 9.85）,low salt concentration(40-80 mmol·L^-1)>high salt concentration(120-160mmol·L^-1).It means that seedlings were able to tolerate to low alkalinity with low salt environments,had average tolerance to medium alkalinity with low salt environments,and could not tolerate to high alkalinity and high salt environments.（3）Through transcriptome sequencing,a total of 474 DEGs were found in plant between saline-alkali group MSA and CK.Among them,364 genes were up-regulated and 110 genes were down-regulated.Analysis of DEGs revealed that the GO pathway was enriched between biological processes and molecular functions.The KEGG pathway was enriched to the highest significance in’zeatin biosynthesis’pathway,followed by the’ABC transport’process.The analysis identified 23Functional DEGs related to saline-alkali stress,mainly involving HSP,ABC transporter proteins,,GLP,SUS,etc.These DEGs may have positive regulation of physiological processes and involvement in some metabolic pathways.This study also screened for six families of transcription factors,MYB,BZIP,WRKY,NAC,ERF and FNR1,involving a total of 10 up-regulated expression of DEGs.The MYB,NAC and FAR1 families are highly expressed under saline-alkali stress and may be key transcription factors to regulate the salinity and alkaline tolerance of Trollius chinensis.In summary,this experiment investigate growth,physiological and molecular response mechanisms of Trollius chinensis seedlings to saline-alkali stress.The index results were analysed to evaluate the tolerance ability of Trollius chinensis seedlings to different saline-alkali stresses,providing a corresponding reference for the promotion of Trollius chinensis in certain areas.This experiment also provided clues for further research on the molecular mechanism of salinity and alkaline tolerance in Trollius chinensis and the cultivation of stress-resistant germplasm resources.