Abstract: 【Objective】 In the study, ethylene accumulation rate, GA levels, IAA content and correlative gene expression levels in leaves of chrysanthemum under low light condition during shade avoidance symptoms was assayed, to explore the shade tolerant mechanism.【Method】Chrysanthemum ‘Puma Sunny’ was assayed under 55% irradiance (control group) and 15% irradiance (low light treatment). GA and IAA contents on 0, 2, 4, 6 and 8 d were measured by high performance liquid chromatograph Agilent 6890N GC system, the relative expression level was measured on 0, 2, 4, 6 and 8 d using GAPDH as reference gene. The concentrations of GA3 were set at 0.5, 1.0, 2.0 and 4.0 mmol·L^-1, with a proper the amount of ethanol dissolution, the final concentration ethanol was 1%. The sample was treated on 4 d and 8 d using the above ground spraying. The concentrations of PAC were set at 10, 20, 50 and100 μmol·L^-1, with a proper amount of ethanol dissolution, the final concentration of ethanol was 1%. The results showed that 2.0 mmol·L^-1 GA₃, and 50 μmol·L^-1 PAC showed impacts on plant growth significantly. After treatment on 0 d and 7 d, the sample was collected on 14 d for analysis of gene expression.【Result】The ethylene level increased markedly on 2 and 4 d, especially on 4 d, and it was 2.04 times more than that of CK. After 6 d, the ethylene level between CK and treatment was not significant. The plant ethylene generation rate under 15% low light conditions was higher than that of 55% irradiance. The gibberellin content in leaves increased significantly on day 2, 4 and 6 compared with the control, the peak appeared on the 6 d, reached 4700.56 ng·g^-1, 2.57 times higher than the control, then decreased quickly, and down to control level on the 8 d. With the prolonging of treatment time, the content of auxin in control group showed an increasing trend, weak light treatment group decreased. On the 8 day, the auxin content in treatment group was 223.95 ng·g^-1 FW, and that in the control group was 489.77 ng·g^-1 FW. The IAA content of the control groupment was 1.12 times higher than that of the treatment group. In the second day of weak light treatment, the expression level of PHYA increased rapidly, 2-6 d with a smaller velocity, 6-8 d kept unchanged, but the control group began to decline from the second day. The change of the expression of PLYA in the treatment group from 4 to 8 day was higher than that of control group. The expression level of PIF4 of the control and the treatment kept the same change trend, from 0 to 6 day the difference was that on 4-8 day the treatment group was higher than the control, especially on the sixth day, it was 1.85 times higher than the control. COP1 gene in control group showed a slow decreasing trend while treatment group increased first and then decreased, the peak appeared on the second day, and on 8 d down to the control group. In the whole process, GAI in the treatment group tended to increase continuously, the control group that in increased slightly on 0-4 day and then declined rapidly. The expression of IAA1 in the treatment group and control group on the 0-2 d increased slightly, and that in the control group on the 2-4 d decreased rapidly. After 2 days, the expression level of IAA1 changed little. Irradiance at 15% induced the PHYA, COP1, IAA1 and PIF4 gene expression. Irradiance at 15% increased GAI transcript level. Exogenous GA inhibited the expression of COP1 and PIF4 expression and down regulated GAI and IAA1 level. PAC inhibited the expression of COP1, PIF4, GAI and IAA1. 【Conclusion】All these data indicated that the expression of PHYA, COP1, IAA1 and PIF4 wasinduced by low light, the GAI transcript level increased under low light. GA and ethylene involved in shade avoidance process of chrysanthemum.

Key words: Chrysanthemum morifolium, hormone level, shade avoidance symptom, gene expression