LAUSR

Abstract Nitrogen is very important to the yield and quality of chrysanthemum. However, excessive application not only negatively affects the yield and quality of chrysanthemum, but also can not be timely absorbed and utilized for chrysanthemum, so causes a lot of waste of fertilizer resources and serious pollution of groundwater environment. Nitrate nitrogen is the main form of nitrogen uptake by the roots of chrysanthemum. The uptake of NO 3 − by plants is mostly achieved by NO 3 − transporters (NRTs) and lateral root formation. However, the morphological structure and molecular mechanism of the response to nitrate signaling in the roots of chrysanthemum are poorly understood. In this study, we investigated that the response to NO 3 − signaling from the viewpoint of roots morphology and anatomical structure, roots NO 3 − contents, endogenous hormones contents and expression of related genes in the roots of chrysanthemum. A hydroponic experiment was performed using the rooted cuttings of chrysanthemum, with KNO 3 treatments (control for Hogland nutrient solution without N element) for seven times at 0, 1, 2, 3, 4, 5, 6 days, respectively. The results showed that the roots morphological indexes increased significantly in the KNO 3 treatments compared to those of the controls at 6 days after treatments, which were associated with the high expression of CmNRT1.1 , CmNRT2.1 , CmNAR2.1 and CmANR1 , which related to NO 3 − transport genes and lateral root development gene, the contents of NO 3 − , indole-3-acetic acid (IAA) and cytokinin (CTK) in the roots and the improved root microscopic structure in KNO 3 treatment. The promoting effect of KNO 3 shows an obvious time-effect. The results from correlation analysis indicated that the responses of chrysanthemum root to NO 3 − signaling could be related with the induction of NO 3 − signaling, the gene expression of NO 3 − transporter genes and lateral root development gene due to regulating the IAA, CTK levels and adjusting the root architecture of the root system.