The Relationship Between The Transcription Factor CBF And The Photoprotective Mechanism In Chilling-sensitive Plant At Low Temperture Under Low Irradiance

As target genes, the CBF genes of Arabidopsis thaliana (Columbia) and sweet pepper(China NO.8) were introduced into tobacco(Nicotiana tabacum cv.Xanthi) byAgrobaterium tumefaciens-mediated transformation with floral dipping method underthe control of CaMV 35S promoter. Physiological functions of these genes andmolecular experiments were analyzed in the transgenic plants and wild types whenthey were exposed to low temperature and low light. On one hand, The Arabidopsis thaliana CBF1 PCR product was inserted intobinary plant vector pROKⅡ . Then it was mobilized to Agrobacterium tumefaciensstrain EHA105 used for plant transformation. The Arabidopsis thaliana CBF1 genewas introduced into tobacco (ecotype Nicotiana tabacum cv.Xanthi) by Agrobateriumtumefaciens-mediated transformation. Then T1 lines were used for experiments. Onthe other hand, we also cloned the CBF gene of sweet pepper by RACE. The analysisfrom amino acid sequence found that it has the CBF character sequences, the nuclearlocalization signal sequences and the two required domains of transcriptor (DNAbinding domain and transcription activator domain). Using the same methodsintroduced the gene to the tobacco and obtained the T0 plants. The transgenic plantswere used for further molecular and photochemical physiological examinations. Themain results were shown as follows:1. The changes of SOD activity at low temperature under low irradiance intransgenic plantsThe SOD activity of ACBF transgenic tobaccos were improved, whichsuggested that the transgenic plants could elevate the cold tolerance. But thePCBF transgenic tobaccos have no obvious changes.2. The changes of soluble protein and sugar at low temperature under lowirradiance in transgenic plantsExposed to the stress for 8-9h, the soluble proteins and sugars of ACBFtransgenic tobaccos were higher than wide type plants. But the PCBF transgenictobaccos have no distinction with wild type.3. The changes of PSⅡ activity at low temperature under low irradiance intransgenic plantsPhotoinhibition was defined that the Photosystem capability decreased whenthe energy absorbed by photosystem was excess than it could be utilized. Usually,The Fv/Fm was used to show the extent of photoinhibition. During 12h at lowtemperature under low irradiance, Fv/Fm of ACBF transgenic plants decreasedslower than wild type ones accompanied by the slight inhibition of their ETR andΦPSⅡ. The increase of NPQ was faster than wild type plants, which idicatedthat when the carbon assimilation was inhibited at low temperature under lowirradiance, NPQ of transgenic tobacco could play the role of dissipation theexcess energy and protecting the photosystem. All these data show that the CBFgene can protect plants from the damages of photoinhibition at low temperatureunder low irradiance, it might be related to the over-expression of itsdownstream genes when CBF1 was introduced to the tobacco.Fv/Fm of PCBF tobacco had the similar results.4. The changes of PSⅠ at low temperature under low irradiance in transgenic plantsP700+ of ACBF and PCBF transgenic tobacco was both kept higher duringstress, which indicated the CBF pathway could protect PSⅠ .The data showed above indicated CBF in transgenic plant could protect thephotosystems, which might be related to its regulating the expression of genes inCBF pathway.