| Winter turnip rape(Brassica campestris L.) is a valuable ecologically beneficial oil crop in cold and arid region of northwestern China. However, coldness and extremely low temperature can make winter turnip rape fail to overwinter and as a result limit its production.In this study, by applying technology of plant physiology and biochemistry,combined with gene cloning and Real-time quantitative PCR, we analyzed effect of the low temperature stress on leaf photosynthetic characteristics, root physiological and biochemical responses on winter turnip rape, and carried out the expression analysis of genes related to cold-resistance in response to coldness stress. The aim of this study is to explore the mechanism of cold resistance and lay a foundation for resistance breeding of winter turnip rape. The specific findings are as follows:1. Diurnal variation of Pn, Tr, CE and Ls were one-peak curve, which reached peak between 12:00 and 14:00, but Ci, Gs and LUE showed “V” curve,2. With decreases of temperature, Fv/Fm, Fv/Fo and Fm/Fo of winter rape obviously decreased, but NPQ rised. The super cold-tolerance winter rape(Longyou 7and Longyou 6) showed the largest decline and the strongest photoinhibition. The Fo and Fm showed the tendency of “drop-rise-drop”. Fs, Fm’, φPSⅡand ETR showed the tendency of drop and The super cold-tolerance winter rape(Longyou 7 and Longyou 6)appeared to decline most steeply.3. During the chlorophyll fluorescence startup, chlorophyll fluorescence parameters had seen significant change under the lower temperature. The fastest startup of chlorophyll fluorescence was super cold-tolerance winter rape, which had the minimum photoinhibition, but poor cold-tolerance winter rape showed the maximum heat dissipation.4. With decreases of temperature, MDA content of super cold-tolerance and cold-tolerance winter rape showed the tendency of “rise-drop”, SS content showed the tendency of “rise-drop-rise”, SP content showed the tendency of drop. The root MDA content of super cold-tolerance winter rape was the lowest. SP and SS content were super cold-tolerance rape>cold-tolerance rape>poor cold-tolerance rape.5. With decreases of temperature, root activity of T-SOD、Cu/Zn-SOD、CAT、APX and GR increased, but POD activity decreased. The enzymatic activity was the strongest.T-AOC showed super cold-tolerance winter rape > cold-tolerance winter rape>poor cold-tolerance winter rape.6. Principal component analysis showed WUE, CE and Pn were the key factors which had an effect on photosynthetic capacity of winter rape. Fv/Fm, Fv/Fo, Fm/Fo,φPSⅡ and Fs were the key factors which had an effect on chlorophyll fluorescence of winter rape. Fs andφPSIIR were the key factors which had an effect on the chlorophyll fluorescence startup. APX, Cu/Zn-SOD and GR activity were the key factors which had an effect on root cold-resistant capability of winter rape. Composite scores for photosynthetic capacity and chlorophyll fluorescence parameters was super cold-tolerance winter rape<cold-tolerance winter rape<poor cold-tolerance winter rape. Composite scores for chlorophyll fluorescence startup and root cold-resistant capability of winter rape was super cold-tolerance winter rape>cold-tolerance winter rape>poor cold-tolerance winter rape.7. The cDNA sequence of APX, Cu/Zn-SOD and Fe-SOD were isolated from Longyou7 by RT-PCR. Semi-quantitative and real time RT-PCR were used to assess the genes expression in response to lower temperature stress. The APX and Cu/Zn-SOD could be induced and enzymatic activity of could be changed by lower temperature and the two genes was a differential expressed gene induced by lower temperature. Fe-SOD was expressed upregulatedly in response to early low temperature stress(4℃). However, the expression of Fe-SOD was inhibited at-4℃and-8℃. SOD activity in roots was higher than that of leaves and super cold-tolerance winter rape was higher than that of poor cold-tolerance winter rape. |
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