| Take autumn Chrysanthemum early-flowering variety'Tangyujinqiu'and late-flowering variety'Xiangyun'as materials, this experiment determined a series of physiological indices and photosynthetic characteristics of the Chrysanthemum leaves under drought and low-temperature stress. By studying the relationship between physiological and photosynthesis indices and the resistance of different species of Chrysanthemum under adversity stress, this paper probed the resistance mechanism, what's more, by applying allogenic material salicylic acid, the action mechanism of salicylic acid on improving Chrysanthemum's cold resistance was studied, which are hoped to provide the theoretical and practical basis for the further research. Studies shows:(1) In drought stress tests, from contrast to severe drought, the RWC in leaves of'Xiangyun'and'Tangyujinqiu'decreased 18.35%,15.81% respectively, which was significant.'Tangyujinqiu'was lower than'Xiangyun'both in decline extent and speed, which showed that'Tangyujinqiu'was better than'Xiangyun'in drought resistance under drought stress.Chlorophyll content of'Xiangyun'and'Tangyujinqiu'is decreased significantly because of drought stress.'Tangyujinqiu'was 3.05 times of'Xiangyun'in Chlorophyll content under severe drought stress. High chlorophyll content in'Tangyujinqiu'guaranteed the high photosynthesis, which could greatly reduce the drought stress influence.(2) Drought stress tests showed: from contrast to severe drought, the relative conductivity of'Xiangyun'and'Tangyujinqiu'raised 23.53%,8.95% respectively, which showed that the cell membrane of'Xiangyun'was hurt more seriously than that of'Tangyujinqiu'.The change of MDA content was similar to that of the relative conductivity. From contrast to severe drought, the MDA content of'Xiangyun'and'Tangyujinqiu'raised 84.86% and 55.34% respectively. Under severe drought stress, the MDA content in'Xiangyun'was 18.65% higher than in'Tangyujinqiu', which showed the cytomembrane of'Tangyujinqiu'was hurt in a less degree.(3) Under drought stress, the soluble sugar content in leaves of'Xiangyun'and'Tangyujinqiu'raised by 117%,55%; the proline content raised by 120.40%,50.69% respectively. It indicated that'Xiangyun'and'Tangyujinqiu'could improve their resistances by inducing soluble sugar and praline.(4) From contrast to the severe drought, the activities of SOD of'Xiangyun'and'Tangyujinqiu'increased 62.88% and 90.96% respectively, the activities of POD of'Xiangyun'and'Tangyujinqiu'increased 40.48% and 52.77% respectively under drought stress. Protective enzyme could help clear up the harmful free radicals in plant body, reduce membrane lipid peroxidation and protect cell membrane system.Under different stress degree, both light compensation point and light saturation point of'Tangyujinqiu'were quite high, which proved its strong adaptive capacity.(5) In drought stress test, compared with the contrast, LCP of'Xiangyun'and'Tangyujinqiu'increased 201.87% and 890.38% respectively; LSP firstly increased and then decreased; Gs decreased 23.12% and 15.92%,Tr decreased 11.82% and 15.92% under severe drought stress.(6) Low temperature led to the declination of chlorophyll content in Chrysanthemum leaves. The chlorophyll content in'Xiangyun'CK declined 30.23% at the temperature of -4℃, and in'Tangyujinqiu'CK declined by 37.75% at the temperature of -8℃comparing with that at 4℃. The chlorophyll content of'Tangyujinqiu'SA was higher than that of'Tangyujinqiu'CK by 40.4%,26.06%,32.88% and 42.00% respectively. The differences were extremely significant, which showed that salicylic acid could relieve the decline of chlorophyll content and enhance the cold resistance of Chrysanthemum.(7) In low-temperature tests, the relative conductivity of'Xiangyun'CK was 38.79% higher than that of'Xiangyun'SA, and in'Tangyujinqiu'CK it was 26.61% higher than in'Tangyujinqiu'SA at the temperature of -8℃. It's indicated that salicylic acid can significantly improve the Chrysanthemum cold resistance. But the difference in the relative conductivity was not significant under other low temperatures. Test showed: under low temperatures, the change of MDA content in'Xiangyun'and'Tangyujinqiu'was similar to that of the relative conductivity, while the level of epicyte membrane liquid peroxidation in'Tangyujinqiu'was higher than in'Xiangyun'. Salicylic acid reduces the membrane liquid peroxidation level, and the differences were not significant.(8) Low temperature test showed: at the temperature of 4℃, the soluble sugar content in leaves of'Tangyujinqiu'CK was 19.84% that of'Xiangyun'CK, and the soluble sugar content of'Tangyujinqiu'SA is 36.84% that of'Xiangyun'SA; at -8℃, the soluble sugar content of'Tangyujinqiu'CK is 205.47% that of'Xiangyun'CK, and the soluble sugar content of'Tangyujinqiu'SA is 150.54% that of'Xiangyun'SA, which showed that the soluble sugar content of'Tangyujinqiu'raised faster. The soluble sugar content of'Xiangyun'SA is 138.79% higher than that of'Xiangyun'CK, and the soluble sugar content of'Tangyujinqiu'SA is 58.56% higher than that of'Tangyujinqiu'CK. Salicylic acid could increase the soluble sugar content and improve cold resistance greatly, and the effect was more obviously in'Xiangyun'. Under low temperature stress, the proline content of'Xiangyun'SA is 55% higher than that of'Xiangyun'CK, and the proline content of'Tangyujinqiu'SA was 76% higher than that of'Tangyujinqiu'CK. The differences were significant, which showed that salicylic acid could improve their cold resistance significantly by increasing the free proline content under low temperature, especially in negative temperature.(9) In low temperature test, the activity of SOD in'Xiangyun'SA increased as temperature fell, and the maximum was 2.73 times the minimum; the activities of SOD in'Xiangyun'CK,'Tangyujinqiu'CK and'Tangyujinqiu'SA reached the maximum at 4℃, and then dropped down; the activitis of APX in'Xiangyun'CK,'Xiangyun'SA,'Tangyujinqiu'CK and'Tangyujinqiu'SA increasd firstly and then decreased. At -4℃and -8℃, the activities of APX in'Xiangyun'SA was 137.01% and 153.26%, higher than that in'Xiangyun'CK; the activities of APX of'Tangyujinqiu'SA was 84.10% and 100.23%, higher than that in'Tangyujinqiu'CK, which showed that salicylic acid could noticeably impact the activity of APX at negative temperature.(10) In low temperature test, comparing with 4℃, Pn of'Xiangyun'CK,'Xiangyun'SA,'Tangyujinqiu'CK and'Tangyujinqiu'SA fell 83.75%, 37.13%, 90.76% and 85.33% respectively,the differences were significant. Pn of'Xiangyun'CK was only 0.33% higher than that of'Tangyujinqiu'CK at 4℃, and'Xiangyun'CK was 76.47% higher than that of'Tangyujinqiu'CK at -8℃, the difference is significant, which may be related to the characteristics of late-flowering.(11) The resistances of different Chrysanthemum varieties were different, which are mainly shown in the chlorophyll, conductivity, MDA, soluble sugar, proline, all sorts of enzyme activities and the net photosynthetic rate, etc.'Tangyujinqiu'presented stronger drought resistance, and'Xiangyun'presented stronger cold resistance, which may be related to the variety characteristics. Salicylic acid could alleviate the impact of low temperature on Chrysanthemum and enhance its cold resistance. |
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