Mechanism On Exogenous Auxin And Gibberellin Signal Induced Seed Dormancy And Germination In Tobacco

By changing hormone signal level in seed germinaton,added exogenous hormones in seed imbibtion stage is of great importance for manual control seed germination and seedling development in tobacco.In this study,Nanjiang 3 was taken as material,seed germination of which was studied through the transcriptome and hormone levels in seed development stage during seed germinaiton.On this basis,the mechanism of gibberellin signal promote seed dormancy release and germination in seed imbibition stage,auxin signal promote seed secondary dormancy and inhibition germination was studied by transcription metabolic network and hormonal balance.The main results were as follows:β Glu I enzyme activity increased in the early stage of seed germination,peaked at about 72 h,and then gradually reduced.ABA content shown a downward trend in the germination process,which were highest in the dry seeds and lowest in the radicle emerging seed.GA₁₊₃ content increased significantly before the endosperm burst.Auxin contents have no significant difference in the germination process.Based on differential expression and time series analysis for the four development period seeds’transcriptome,the results show that seed metabolism recovered in the wateruptake stage,the hydrolysis metabolism of the cell walls has resumed during imbibitions,metabolics of cell division,proliferation and differentiation were activity after imbibitions,and photosynthesis metabolism was induced in radicle emerging seeds.Oxidative stress,hormone signal and energy metabolism were active in the whole process of seed germination.Tobacco seeds primed with 100mg/l GA3 solution showed increased speed and uniformity of radicle emerge.GA₁₊₃ lever and β-1,3glucanase activity of which were significantly higher respectively at the germination starting and pre-endosperm rupture stage.Transcriptome of the two kinds of primed seeds were more similar with each other than compared with the unprimed seeds.The transcripts,for which their expression patterns were significantly up-or down-regulated both in GA-and hydro-primed seeds relative to unprimed seeds were focused upon,93.90%of which after priming and 83.89%in radicle expanding were regulated in the same manner respectively.Enrichment analysis revealed that GA promoted seed germination was associated with phytohormones metabolism and（or）signaling,special amino acids metabolism,glutathione metabolism at seed germination starting stage,and photosynthesis,redox signaling,glyoxylate cycle,protein synthesis at the stage of pre-endosperm rupture.Tobacco seeds soaked in 1000mg/l auxin solution showed markedly decreased germination compared with that in low concentration of auxin solutions and ddH2O.Using an electron microscope,observations were made on the seeds which did not unfold properly in comparison to those submerged in ddH20.The radicle traits measured by WinRHIZO,were found to be also weaker than the other treatment groups.Quantified by ELISA,there was no significant difference found in β-1,3glucanase activity and abscisic acid（ABA）content between the seeds imbibed in gradient concentration of auxin solution and those soaked in ddH₂0.However,gibberellic Acid（GA）and auxin contents were significantly higher at the time of exogenous auxin imbibition and were gradually reduced at germination.RNA sequencing（RNA-seq）,revealed that the transcriptome of auxin-responsive dormancy（auxin-responsive germinated）seeds were more similar to that of the imbibed（common germinaed）seeds when compared with primary dormancy（secondary dormancy）seeds by principal component analysis.The results of gene differential expression analysis revealed that auxin-controlled secondary seed dormancy was associated with flavonol biosynthetic process,gibberellin metabolic process,adenylyl-sulfate reductase activity,thioredoxin activity,glutamate synthase（NADH）activity and chromatin regulation.In addition,auxin-responsive germination responded to ABA,auxin,jasmonic acid（JA）and salicylic acid（SA）mediated signaling pathway（red,far red and blue light）,glutathione and methionine（Met）metabolism.