| Four-years-old petals of Magnolia denudata, M.liliflora and M.soulangeana as materials were used to research their cold resistance and chromogenic mechanism of flowers in Baoding area. Super-cooling points, relative electrolyte leakage, browning rate in all blossom and osmotic adjustment substance, anti-oxidant defense substance content, protect enzymes, floral color index, pigment content in full blossom after lower temperature treatment were determined as well as the relative indexes about the floral variation in flowering stage in order to discuss the cold resistance and chromogenic mechanism of flowers, some main conclusions were summarized as follows:(1)The super-cooling points in different flowering stage of 3 Magnolia petals have significant difference. For the same species the super-cooling point of the bud stage was the lowest, first stage second and full stage the highest. In the buds, Magnolia liliflora had the lowest super-cooling point, Magnolia soulangeana second, Magnolia denudate the highest. Both the first and full blossom, Magnolia soulangeana had the lowest, super-cooling point, Magnolia liliflora second and Magnolia denudate the highest.(2)Relative electrolyte leakage and browning rate had a negative correlation with the temperature variation after the low temperature treatment. Moreover it had a high goodness of fit with the Logistic equation. After calculating the low semi-lethal temperature according to the Logistic equation, we found that buds were lowest, first blossom second and full blossom the highest.(3) As the temperature dropped, the MAD contents and O2- generation rates increased gradually, having the same changing trend with the variation of relative conductivity and a significantly negative correlation with the treatment temperature. Among this M. denudata has the largest rising while Magnolia liliflora the smallest.(4) With the increase of the low temperature stress, the osmotis adjusment substances of the 3 kinds of Magnolia have different trends. Soluble protein may be the main osmotic regulation substance after low temperature stress. Soluble sugar contents were the main osmotic regulation substance in the process against low temperature.(5) The contents of ASA and GSH were in increasing trends and then decreasing of the 3 Magnolia kinds, while having the different extent. Of which the contents of the two substance of M.soulangeana were significant higher than the others, which indicated that its hardness against cold were stronger than the other two.(6) SOD、POD、APX and GR activity all had a first up then down trend of the 3 Magnolia, at the beginning of the low temperature, the protect enzyme decreased, which indicated that the ability of eradicating the O2- strengthened. When the low temperature strengthened, the plant cells over oxidation deepen, and the protect activity decreased.(7) The cold-resistant ability of this 3 Magnolia in full blossom was evaluated comprehensively using subordinate function method and the main results was Magnolia soulangeana had stronger cold-resistant ability, followed Magnolia liliflora, and Magnolia denudata had poorer cold-resistant ability.(8) Low temperature impact the floral color of the 3 Magnolia species, for M.soulangeana and M.liliflora, as the temperature lowered, the lightness L*-value, chromatic component a*-value and C*-value decreased. Meanwhile low temperature stress was a hinder to the synthesis of anthocyanin and flavonoid, disordered the activity of relative enzymes and seriously affected the normal color expression of the 3 Magnoliaa species.(9)Under natural state, with the passage of the blooming, the lightness strengthened, red and colorful index wreaked, PAL and CHI activity abated, pH index increased continually and soluble sugar, anthocyanin, and flavonoid content decreased rapitidly, and the anthocyanin and flavonoid contents have a significant difference during different flowering stage of the 3Magnolia. |
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