| Auxin plays key roles in many developmental processes,such as embryogenesis,organogenesis,cell determination and division,and tropical responses.The processes are finely coordinated by polar and asymmetric distribution of auxin within tissues and cells.The plant-specific auxin efflux proteins PINFORMED(PIN)have been well characterized in many plant species,where they are crucial in controlling the transport of auxins in various aspects of plant growth.But little is known about the exact functions of the PIN genes in the Nicotiana tabacum during plant growth.This study of gene expression pattern can provide guidance for the study of gene function.In order to explore the expression pattern of NtPIN genes in tobacco,the promoters of NtPIN1a,NtPIN2a,and NtPIN4 genes were cloned first and their possible cis acting elements were predicted by using the promoter's analysis websites.Then,we constructed the transgenic tobacco driving GUS reporter gene driven by the promoters.GUS staining analysis of transgenic tobacco seedlings under normal conditions and abiotic stresses(Salt stress,low potassium stress and osmotic stress)and auxin(IAA)was carried out to understand the expression pattern of NtPIN1a,NtPIN2a and NtPIN4 gene promoters in the process of seedling germination and growth.In addition,salt stress is the most serious ion stress,and the cultivation area affected by salt stress is growing,which seriously affects the physiological and biochemical reactions in plants,resulting in the reduction of grain production and threatening food security.To study the physiological and biochemical responses of different cultivated tobacco varieties under salt stress can provide data support for understanding the salt tolerance mechanism of Solanaceae crops.Therefore,the physiological and biochemical indexes of three tobacco varieties under different degrees of salt stress were studied by using HonghuaDaJinYuan(H),K326(K)and Zhongyan100(Z)as experimental materials.The main results are as follows:1.In silico analysis of the NtPIN promoters confirmed the existence of common core promoter elements including CAT-box,CAAT-box,TATA-box,hormone and abiotic stress responsive elements such as ABRE,P-box,MYC,MYB and Myb-binding sites.2.The expression pattern of the NtPIN1a,NtPIN2a and NtPIN4 genes under abiotic stresses and hormone are as follow:The transgenic tobacco plants with promoter of NtPIN1a exhibited a promising expression of GUS in seed germination,root tips,shoot meristem and developing leaves under normal condition.While the differential expression of GUS in moderate salt,drought,low potassium stresses and externally applied auxin at two different time points,suggests the role of NtPIN1a in growth processes and environmental stress conditions.The expression of NtPIN2a is very low and express in the germination stage and also in the apical meristem under stresses conditions.However,the expression of NtPIN4 is not visible in either stage of seed germination and also under hormone and abiotic stresses conditions.3.Differences in response of three tobacco varieties to salt concentration:HonghuaDaJinYuan was the least affected one among the other varieties in terms of reduction in fresh plant weight as salinity stress increases.Salt stress augmented the chlorophyll content in H and K,while a decline was observed Z as salt stress increased.Chlorophyll fluorescence imaging system is also used to know about the photosynthetic efficiency of plants.Salt stress reduced the PS? quantum yield(QYLss)in all the three varieties,which was also supported by a reduction in photochemical quenching coefficient(qP?Lss).Similarly,steady-state non-photochemical quenching(NPQ?Lss)increased in H and Z only,which was also supported by an increase in the steady-state non-photochemical quenching coefficient(qN?Lss)in response to various salt stress treatments.Based on the physiological data demonstrated,it is suggested that H and K are tolerant cultivars to salinity stress,while Z is a sensitive variety. |
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