Abstract: 【Objective】 In order to reveal the root morphology and molecular basis of the response of nitrate nitrogen to root development of chrysanthemum, and provide a basis for chrysanthemum breeding to improve the efficiency of nitrogen, this study was carried to investigate the changes of root morphology and structure, the contents of nitrate nitrogen and endogenous hormones, the nitrate nitrogen transport genes and root formation gene of chrysanthemum. 【Method】 The rooted cuttings of chrysanthemum were used in water-culture system in this experiment, then treated by 10 mmol·L^-1 KNO₃ while control was treated with Hogland nutrient solution without nitrogen. On the day 0, 1, 3, 7, 14, 21 and 28 after treatment, anatomical structures were observed, the contents of NO₃^-, IAA and CTK in the roots and leaves were measured, the cDNA conserved sequence fragments of CmNRT1.1, CmNRT2.1, CmNAR2.1 which were identified as the NO₃^- transport protein genes and CmANR1 which were identified as the lateral root differentiation gene of the roots were cloned, and the relative expression levels of them were observed using quantitative real-time PCR. 【Result】The results showed that: There were no significant differences were observed in the overall length, average diameter, total surface area and total volume of roots between NO₃^- treatment and control within the first 3 days, they were increased significantly after 7 days compared with those of control. The cross sections of roots were also observed on the day 28 after treatments. The vascular bundle diameter of the 1st root, 2nd root and 3rd root after NO₃^- treatments were increased significantly compared with those of control. The ratios of vascular bundle to root diameter of the 1st root, 2nd root and 3rd root were significantly increased compared with those of controls. The NO₃^- contents of chrysanthemum reached the peak on the day 7 (0.45 mg·g^-1 FW) in the roots and on the day 14 (0.35 mg·g^-1 FW) in the leaves, respectively, then both of them decreased slightly, but they were maintained higher level compared with those of control on all days. Compared with those of control, the contents of IAA and CTK in roots and leaves in the NO₃^- treatments were significantly increased. The peaks of the contents of IAA and CTK in the roots appeared on the day 7 and those of in the leaves appeared on the 14 day after treatments, while the IAA and CTK contents of controls showed no significant change. The relative expression levels of CmNRT1.1 gene’s peak were appeared on the 1 day after treatment (the control also on the day 1). The relative expression levels of CmNRT2.1 and CmNAR2.1’s peaks were appeared on the day 3 after treatment (the control slightly increased on the day 3 and remained relatively stable). While the relative expression levels of CmANR1 reached the peak on the day 7 after treatment (the control on the day 14), and the relative expression levels of the 4 genes maintained higher levels than those of control throughout the experiment. The results showed that the 4 genes were induced by nitrate, and their expression trends were similar, which were increased at first, decreased later and then remained relatively stable. 【Conclusion】 The roots of chrysanthemum could respond to nitrate signal in the growth medium. The response is realized through the expression of nitrate transporter genes and lateral root development gene, and then adjust the configuration of the roots to improve the absorption and utilization of nitrate in chrysanthemum roots.

Key words: Chrysanthemum morifolium, root, NO₃^-, endogenous hormones, gene expression