| Chloroplasts are the specific organisms of the plants.They are crucial to their photosynthesis and growth development The chloroplast small heat shock protein is usually the most heat responsive of the chloroplast HSPs.Chloroplast studies in vitro indicate that the choloplast sHSP are related to the thylakoid membranes in response to heat stress.When the proteins are induced,the increase of their expresstion is positively correlated with PS II (Photosystem II ) thermotolerance and the whole-plant thermotolerance .In plants,active oxygen species are inevitably generated during photosynthe -sis,and the major site of generation of these toxic species is the chloroplast under both unstressed and stressed conditions.lt has been recognized that the chloroplast sHSP have protective functions against oxidative stress,and this functions are corr-elated with its unique Met-rich domain.Recently, studies show that heat shock proteins especially the sHSP have protective roles against cold stesses besides high temperatures. In fact,it has been reported that mitochondrion sHSP ,cytosolic sHSP and ER sHSP are related to the ability of cold-tolerance.But it does not know if the chloroplast sHSP has the same pretective functions against cold sresses too.The chloroplast sHSP gene was screened from the cDNA library of tomato flower by PCR strategy and confirmed by sequencing.But difference was found at 3 bases of the sequence from the reported in Genbank.Then,an integrated vector pROK II of the chloroplast sHSP gene and NPTII gene(a kanamycin resistant gene) with CaMV35S promoter was constructed and introduced into tomato mediated by Agrobacterium tumefaciens LBA4404.Transgenic tomato were screened by their ability of growing on media containing kanamycin. The genomics DNA of the transformants was extracted and assayed by PCR with NPTII primer CaMV35/CP primer and the results indicated that the chloroplast sHSP gene has been integrated into the genomics of the tomato.Then the transgenic tomato were exposed to low temperature(in winter,on natural condition,the top temperature was 15 癈 and the lowest temperature was 5℃and a set of physiology parameters were measured after 6weeks.The results were shown as follows:1) Effect on growthHeight of the transgenic tomato and the control plants after 6 weeks at low temperature showed that the transformants had been grown faster than the control.In addition,the leaves of the control plants appeared to be much reder than the transgenic tomato,and the change were obvious followed by far from the treated time at low temperature,which suggested that the constituently expression of the chloroplast sHSP had some protective fountions to the tomato at low temperature.2) Effect on contents of MDAMDA is the product that membrane lipid peroxide and the contents of MDA in plants can reflect the degree of the damage that the plants are encountered to some extent.The measurement results show that the accumulation of MDA in transgenic tomato were lower than that of the control,which suggested that the cell membrane system was damaged under the low-temperature stresses ,meanwhile the transformants suffered the little damage than the control plants.3) Effect on chlorophyll contentsThe chlorophyll is the important pigment for the photosynthesis of plants.The measurement results showed that the chlorophyll contents in transgenic tomato were highter than that of the control,which indicated the damage extent that the chlorophyll in transformants suffered was down to that of the control plants at low temperature.4) Effect on photosynthesis:The important parameters of photosynthesis such as net photosynthetic rate, transpiration rate, stomatal conductance and substomatal CO2 concentration were measured and the results was that the first three parameters of the transgenic tomato were highter than that of the control plants,and the last one was lower than the control tomato,which indicated that the photosynthesis of transgenic tomato were stronger than control clearly.All th...
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