Study On Dynamic Of Potassium Accumulation And Characteristics Of Potassium-enriched Genotype In Flue-cured Tobacco

Potassium?K?,an essential microelement in the plant development,plays an important role in plant growth,metabolism,enzyme activity and osmotic adjustment.Tobacco has a high requirement for K.K not only plays an important role in plant growth and physiological metabolic process,but also benefit for the resistance of disease and pest.K content in tobacco leaf is considered to be an important indicator of tobacco leaf quality.However,poor nutrient in soils becomes severer and severer in China.Low K content and low availability of K in soils result in low content of K in tobacco leaf.In this study,K-enriched genotypes of flue-cured tobaccos were screened from 70flue-cured tobacco germplasm resources by two-year field experiments firstly.Then,the rhizosphere soil characteristics,root response,physiology and biochemistry characteristics of the K-enriched genotype of flue-cured tobaccos were investigated.Meanwhile,the K accumulation in tobaccos among growth stages were also investigated by RNA-Seq technology to find the gene difference among K accumulation stages and further the specific gene expression modules associated with K accumulation among stages.The main results were as follows.1.K content and K accumulation in leaves of the 9 tobacco cultivars presented similar trend of“Two Humps”,which were observed at later vigorous growth stage and middle leaf mature growth stage.There was one peak for K accumulation in lower leaves at the middle leaf mature stage.Two peaks were observed for K accumulation in middle leaves and upper leaves at the vigorous growth stage and middle leaf mature stage.There was some difference for the time of peak appearance among the genotypes.The dynamics of K accumulation in tobacco leaves present great practice in adjusting K fertilizer topdressing stages and optimizing K content in tobacco leaves.According to the field experiment,K content in tobacco leaves increased by more than 2%when topdressing K fertilizer at the K accumulation peak stage.2.Significant difference was observed for the K content among the genotypes of the 70flue-cured tobaccos.The Gajihongda,Changyehongda,K326 and KRK26 were screened as the K-enriched genotype of flue-cured tobaccos and presented high K content in leaves for the two-year field experiments.These four tobaccos showed great advantages in application and also provided parent material for the breeding of K-enriched genotype of flue-cured tobaccos.3.The available potassium?AK?and slowly available K in rhizosphere soils of the K-enriched genotypes?KRK26 and K326?were significantly higher than those of the low-K genotype?Bina 1?.The AK in rhizosphere soils of the two genotypes of tobaccos was significantly greater than that in bulk soils among different K applications.The slowly available K in rhizosphere soils of the K-enriched genotypes was significantly higher than that in bulk soils.The slowly available K in rhizosphere soils of the low-K genotype were significantly lower than that in bulk soils.The urease and catalase activity and pH in rhizosphere and bulk soils of the two genotypes decreased with the increasing K application,while the sucrase activity increased with the increasing K application.The urease and catalase activity in rhizosphere soils of the low-K genotype were significantly lower than those of the K-enriched genotypes with lower K application of 75 mg kg^-1 and 150 mg kg^-1.There was no difference for the sucrase activity among the genotypes.4.The total root absorption area and actively absorption area of the low-K genotype of T44 significantly increased with the increasing K level,and those of the K-enriched genotype of T29 and T32 showed no significant change among different K levels.The total root absorption area and actively absorption area of T44 were much more sensitive to K application level,and those of T29 and T32 were not sensitive to K application level.The root activity of all genotypes showed greatly decreased with the increasing K level,and the low-K genotype showed greater decrease than the K-enriched genotypes.The genotypes showed significant influence on root activity with the treatment of 0.02 mmol L^-1 K.The genotype and K level showed no significant influence on CEC of tobacco roots.The K level presented greater influence on the release of H⁺by roots than the genotypes.Greater release of H⁺by roots of K-enriched genotypes was observed with higher K level.The release of H⁺by roots of low-K genotype reached the maximum with 0.20 mmol L^-1 K application.The release of H⁺by roots of K-enriched genotypes was significantly lower than that of the low-K genotype with the same K level.5.The biomass of root,stem and leaf of K-enriched genotypes?T29 and T32?was significantly greater than that of low-K genotype?T44?among K applications.The K content in leaf of K-enriched genotypes were significantly higher than that of low-K genotype among K applications.However,K content in root of low-K genotype was significantly higher than that of K-enriched genotypes under low K stress.The chlorophyll content in the K-enriched genotypes under low K stress was similar with that with general K application.The chlorophyll content in the low-K genotype decreased significantly under low K stress.The SOD activity of the three genotypes significantly increased with the increasing K application.The SOD activity of the K-enriched genotypes was higher than that of the low-K genotype at the vigorous growth stage and middle leaf mature stage.The SOD activity of all genotypes at the vigorous growth stage was much more sensitive to low K stress,and the SOD activity of the low-K genotype was more sensitive to low K stress than the K-enriched genotypes.At the vigorous growth stage and middle leaf mature stage,both the NR activity and sucrase activity of all genotypes significantly increased with the increasing K applications.6.RNA-seq technology was employed to characterize the transcriptome of the Chuanyan1 collected from Sichuan and Coker176 obtained from abroad,according to the previous study of K accumulation characteristics of flue-cured tobaccos.Each sample obtained more than 14801735?4.4 Gb?raw reads with good quality among different K accumulation stages.The de novo transcriptome assembly and gene prediction were carried out with the reference genome of N.tabacum K326.The 49255 genes from the database accounted 97.14%of the total reference genes,and which including 1362 new genes.According to the WGCNA analysis of Chuanyan1 and Coker176 among 5 K accumulation stages,22 modules with high gene co-expression were obtained.Further correlation analysis of the 22 modules with K accumulation phenotype found 4 specific modules consistent with the 5 K accumulation stages.The genes from the 1^st and 2^nd modules presented similar trend with K accumulation.For the 2^nd module,Chuanyan1 and Coker176showed opposite gene expression,demonstrating that there were some similar regulation genes in K accumulation process and also some difference between the two genotypes.The3^rd and 4^th modules presented some stage difference in the process of K accumulation.