Studies On The Mechanisms Of Enhanced Chilling Tolerance In Tobacco Transformed With BADH Gene

In the present study, we attemped to elucidate the mechanisms that synthesis of betaine protects the transgenic tobacco plants with BADH gene against chilling stress. The main results are as follows:(1) Chilling stress resulted in a decrease in CO2 assimilation and such a decrease was much greater in wild type plants than that in transgenic plants. During chilling stress, transgenic tobacco plants maintained higher photosynthetic rate and enhanced the tolerance to chilling stress.(2) The analysis of chlorophyll fluorescence demonstrated that photosystem II(PSII)in transgenic plants showed higher chilling tolerance than in wild type plants, suggesting that the accumulation of GB leads to increased tolerance to low temperature-enhanced photoinhibition. This increased tolerance was associated with an improvement of oxygen-evolving complex and the reaction center of PSII to chilling stress.(3) Chilling stress induced a significant accumulation of H2O2 , O2- in wild type and transgenic plants, but this accumulation was much less in transgenic plants. GB decreased the accumulation of ROS through maintain relatively higher antioxidant enzyme activities and antioxidants content.(4) GB accumulation in vivo increased the cFBPase activity, improved the synthesis of sucrose.(5) During chilling stress, transgenic plants changed the lipid content in the thylakoid membrane of tobacco leaves, this would lead to increase the stability of thylakoid membrane. The relative higher PG contents in transgenic plants maybe important in mitigating the degradation of LHCII which binding to PSII.(6) GB in vivo increased the the ratio of polyunsaturated fatty acids. Transgenic plants could maintaine higher contents of 16:1(3t) of PG.(7) The expression of HSP70 was induced by chilling stress in transgenic and wild-type plants. HSP70 contents of transgenic tobacco plants were higher than that of wild-type tobacco, and the increased HSP70 maybe associated with the enhanced chilling tolerance in transgenic plants.In conclusion, the mechanisms of the enhanced chilling tolerance in transgenic tobacco plants with BADH gene maybe associated with the followings:Transgenic tobacco plants decreased the damage induced by ROS to photosynthetic apparatus through maintaining relatively higher antioxidant enzyme activities and antioxidants content. The higher activity of cFBPase that important for sucrose synthesis in transgenic tobacco plants may mitigate the feedback of photosynthesis.GB in vivo changes the lipid contents and the composition in the thylakoid membrane of transgenic tobacco plants, thereby improveing the stability of thylakoid membrane under chilling stress.GB in vivo increased the amount of HSP70 both in the soluble stroma and the thylakoid membranes in transgenic tobacco plants, this maybe a part of the mechanism of enhanced chilling tolerance in transgenic tobacco plants with BADH gene.