The Relationship Between Arabidopsis Transcription Factor CBF1 And The Photoprotective Mechanism In Lycopersicon Esculentum Mill At Low Temperture Under Low Irradiance

Low-temperature may cause damages which include many aspects such as the change of the membrane lipids phase, the permeability increase of the membrane and the level of reactive oxygen species, the accumulation of some secondary metabolites, and so on, to plants. All these phenomena result from the damages of some enzymes which were involved in the metabolism of plants cells. Photosystems are also very sensitive to low temperature stress, under the low temperature stress Reactive Oxygen Species(ROS) accumulates a great deal, which results in photo apparatus being destroyed because of oxidation stress, Light-harvesting ability , Fv/Fm and other indices all decease, at this times enzymes that catalysize photo dark reaction also reduce , at last appear siganificantly reducing .the CBF genes of Arabidopsis thaliana (Columbia) are the target genes, The Arabidopsis thaliana CBF1 plant vector pROKⅡwere introduced into Lycopersicon esculentum Mill by Agrobaterium tumefaciens-mediated transformation with floral dipping method under the control of CaMV 35S promoter and obtained the transgenic plants. Physiological functions of these genes and molecular experiments were analyzed in the transgenic plants and wild types when they were exposed to low temperature and low light.1. The changes of PSⅡactivity at low temperature under low irradiance in transgenic plantsAfter stress for 3d at low temperature under low irradiance, Fv/Fm of ACBF transgenic plants decreased slower than wild type ones accompanied by the slight inhibition of their ETR andΦPSⅡ. The increase of NPQ was faster than wild type plants, which idicated that when the carbon assimilation was inhibited at low temperature under low irradiance, NPQ of transgenic Lycopersicon esculentum Mill could play the role of dissipation in the excess energy and protecting the photosystem. All these data show that the CBF gene can protect plants from the damages of photoinhibition at low temperature under low irradiance, it might be related to the over-expression of its downstream genes when CBF1 was introduced to the Lycopersicon esculentum Mill2. The changes of PSⅠat low temperature under low irradiance in transgenic plants P700+ of ACBF transgenic Lycopersicon esculentum Mill was both kept higher during stress, which indicated the CBF pathway could protect PSⅠ.The data showed above indicated CBF in transgenic plant could protect the photosystems, which might be related to its regulating the expression of genes in CBF pathway.3.The changes of chloropy11 content:low-temperature can restrain the biosynthsis of chlorophyll and destroy its structure. The contents of chlorophyll a, chloropy11 b and chlorophyll a+b in controls were significantly lower than that in transgenic seedlings. But The ratio of chlorophyll a/b is higher than that in transgenic seedlings. These results suggested that the transgenic plants have much more ability to adapt the chilling and low irradiance.4.The changes of SOD activity at low temperature under low irradiance in transgenic plantsThe SOD activity of ACBF transgenic Lycopersicon esculentum Mill were improved, which suggested that the transgenic plants could elevate the cold tolerance.5. MDA content: the contents of MDA in controls were significantly higher than that in transgenic seedlings.6. The changes of soluble sugar at low temperature under low irradiance in transgenic plantsAfter chilling stress under low irradiance, the soluble sugars of transgenic tomato were higher than wide type plants. The results suggest that low-temperature can cause damages to the wild type. However, with the existence of large number of CBF1 which act as molecular chaperones, the transgenic tomato deduced the damage effect of cold stress at the same instance. So, we can concluded that over-expressed constitutively CBF1 can improved the cold-resistance of tomatoes indeed.