| HSP90 family is a highly conserved group of constitutively proteins,which was essential, abundant at normal temperatures, comprising 1–2% of cellular proteins under unstressed cells,and stimulus can increase there expression. In vivo HSP90 is a dimeric protein constituted by three regions: the N-terminal domain which binds the ATP, the central domain involved in the ATPase activity and in the recognition of client proteins and the C-terminal domain responsible for the dimerisation and binding of several co-chaperon.HSP90 has no activity before it's dimerisation.The HSP90 family is a kind of special ATP-dependant molecular chaperone essential to the activation and regulation of a large number of protein involved in cell signalling and regulation.The early studies suggested that they could be propitious to the renaturalization of a series of denatured proteins by exposure to high-temperure or other environmental adversities. Resent studies presumed that Under non-stress conditions HSP90 seemed to perform more general functions in regulation the activity of many clint proteins,such as DNA replication,transcription, intracellular transport of proteins, signal transformation, immune responses,growth,development and apoptosis, etc.A cDNA of 2588bp encoding a full-length Lehsp84 had been cloned from Lycopersicon esculentum,which is a chromogene.The result of sequence analysis showed that the HSP84 ,locating in cytoplasm,was a kind of HSP90 family. In this experiment,an integrated vector pROKⅡof the Lehsp84 gene and NPTⅡgene(a kanamycin resistant gene) with CaMV35S promoter was constructed and introduced into tobacco mediated by Agrobacterium tumefaciens LBA4404. The result of PCR indicated that the Lehsp84 gene has been integrated into the genome of the tobacco. The results of Northern indicated that the Lehsp84 gene has been constitutively expressed in the tobacco. The main results were shown as follows:1) PCR and Northern Blot productions: The result of PCR showed that the tobacco plants transformed Lehsp84gene had been amplified DNA segments with the NPTII primers, while the control plants haven't,which indicate that Lehsp84 gene had been transformed into the tobaccos.The Northern blot showed that the expression of Lehsp84 in transformed tobacco was higher than that in the controle plants.It indicated that external Lehsp84 gene had been constitutively expressed in the tobacco.2) Thermotolerance of the transgenic plants:The control plants and the the transgenic plants were exposed to high temperature of 48℃and 50℃for 6h, and then were transferred to normal conditions for recovery for 10-20 days .The results showed that transgenic plants t after 48℃-stress could grow well, while the control plants had been impaired greatly. And all the control plants died quickly during the recovery after a 50℃treatment,while a few of the transgenic plants germinated again after a few days. It indicates that overexpression of HSP84 could improve the thermotolerance of the tobacco plants.3) Salt resistance of the transgenic tobaccos: The control plants and the transformed were irrigated with Hogland containing 0,100mM and 150mM NaCl for 7-8 days.The content of MDA and activity of superoxide dismutase (SOD) in plant leaves were measured.The results showed that the content of MDA in Lehsp84-transformed toacco was lowerer than that in control plants,while the activity of SOD was higher comparatively,but the difference between them was not notable.The influence of a series of NaCl concentration on tobacco viability had no distinct difference between the transformed and the untransformed .These results lead to a conclusion that overexpression of HSP84 couldn't enhance the salt resistence of the tobacco.4) Cold resistance of the transgenic tobaccos: After having been placed under the low temperature of 5-7℃for 3 weeks, the difference of growth potential between the transgenic plants and untransformed had not been observed.The measurement of MDA content and SOD activity had the same result .W can conclude that overexpression of HSP84 couldn't improve the cold resistance of the transgenic tobaccos..
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