| Parakmeria is a kind of megaphanerophyte evergreen tree. It has straight trunk, beautiful shape, lush branches and leave. It is resistant to low temperature and high temperature, grow well in the central city area, has high landscape and ecological value.In order to ascertain the cold resistance mechanism of Parakmeria,7 years plants of Parakmeria lotungensis, Parakmeria omeiensis, Parakmeria yunnanensis, Parakmeria nitida, Parakmeria lotungensis var. Xiangxiensis and 1 year,7 years,15 years plants of Parakmeria lotungensis were researched as materials. The relative conductivity, malondialdehyde content, superoxide disproportionation activity, peroxidase activity, soluble protein content and free proline content of vitro leaves of each species were measured under different temperature (5℃,0℃,-5℃,-10℃,-15℃ and -20℃) at five time points in the process of the winter (in early November, the middle of December, the middle of January, early February and early March). The lethal temperature of each species were fitted out cooperated with Logistic equation. The correlation analysis of indexes and low-temperature stress were done. The subordinate function value of each species were determined using the method of subordinate function. The cold-hardiness of each species were comprehensive evaluated. The results are summarized below:(1)During natural decreasing process of air temperature, physiological indexes of 5 kinds of Parakmeria had similar variation trends. The relative conductivity and malondialdehyde content had positive correlation with minimum mean temperature, while superoxide dismutase, peroxidase activity, soluble protein content and free proline content had negative correlation with minimum mean temperature.(2)During artificial low temperature stress process, physiological indexes of 5 kinds of Parakmeria had similar variation trends. The relative conductivity, malondialdehyde content and free proline content had negative correlation with artificial stress temperature, while superoxide dismutase, peroxidase activity and soluble protein content had positive correlation with artificial stress temperature.(3)The lethal temperature of 5 kinds of Parakmeria had positive correlation with minimum mean temperature. The order was:Parakmeria lotungensis< Parakmeria nitida < Parakmeria lotungensis var. Xiangxiensis< Parakmeria omeiensis< Parakmeria yunnanensis. The cold-hardiness of 5 kinds of Parakmeria were comprehensive evaluated with the method of subordinate function. The order was:Parakmeria lotungensis> Parakmeria lotungensis var. Xiangxiensis> Parakmeria omeiensis> Parakmeria nitida> Parakmeria yunnanensis.(4) The lethal temperature of 3 kinds of Parakmeria lotungensis at different tree-age decreased as air temperature fell. The order was:1 year< 7 years< 15 years, which had negative correlation with tree age. The cold resistance of 3 kinds of Parakmeria lotungensis at different tree-age were comprehensive evaluated with the method of subordinate function. The order was:15 years> 7 years> 1 year. |
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