To measure metal ion content, about 500 mg of shoots and roots were firstly separated from Chrysanthemum plants, respectively. Then, the dried samples were ground and digested with 15 ml nitric acid (HNO3)/perhydrol (H2O2) (3:1, v/v) in a microwave system (MARS, CEM) at 160°C for 20 min. After centrifugation at 12,000 rpm for 10 min, the supernatant was used for determining metal ion contents by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Thermo Scientific, Waltham, MA, United States) as described recently by Lei et al. (2014).