Abstract: 【Objective】 To explore the relationship among exogenous selenium, endogenous melatonin, and glutathione oxidation cycle, the effects of selenium valence states and concentrations on melatonin content and glutathione (GSH) redox cycle efficiency in sweet cherry leaves were studied.【Method】Field experiments were carried out at Guangyuan, Sichuan in 2015. Two-year old sweet cherry of ‘Hongmi’ and ‘Brooks’ in orchard were chosen as the experimental materials. Five treatments of water treatment (CK), Se⁶⁺ (from Na₂SeO₄), Se⁴⁺ (from Na₂SeO₃), Se⁶⁺ + melatonin, Se⁴⁺ + melatonin were designed. The leaves were collected and ground to measure the contents of Se and melatonin after treated 30 days. The vitro experiments were carried out in 2016, and the leaves of two-years old ‘Brooks’ in orchard at Qijiang, Chongqing were selected as materials. For the different treated time experiments, the leaves were placed in 2 mg·L^-1 se⁶⁺ for 0, 1, 2, 3 and 4 days, and water treatment as control (CK), and the leaves were collected at 10:00 am. every day. For the different Se concentrations treatments, sweet cherry leaves were placed in 0, 0.5, 1.0, 2.0 and 4.0 mg·L^-1 se⁶⁺ solution for 24 hours and then collected the leave samples. The contents of selenium and melatonin, and substances and enzymes in glutathione redox cycle of all collected samples were measured. 【Result】 Leaves melatonin contents of ‘Hongmi’ and ‘Brooks’ under Se⁴⁺ or Se⁶⁺ treatments were significantly reduced under field experiment. While leaves melatonin contents of two varieties sweet cherry under Se⁶⁺+ melatonin or Se⁴⁺+ melatonin treatments were higher than only Se⁴⁺ or Se⁶⁺ treatments, respectively. For different time vitro treatment, leaves melatonin contents under Se⁶⁺ treatment was significantly higher than control at the first day, but the contents were become lower than water control at 2, 3 and 4 days. At the same time, vitro leaves under 2 mg·L^-1 Se⁶⁺ concentration for 24 h reduced GSH redox cycle efficiency at first day, via the contents of GSH, oxidative glutathione (GSSG), GSH+GSSG and GSH/GSSG ratio were all lower than control, and the activities of peroxidase (GPX) and glutathione reductase (GR) were also lower than control. But after that GSH redox cycle efficiency started to increase and was higher than control. For different selenium concentrations treatments, the vitro leaves melatonin contents and GSH redox efficiency were reduced with the increased Se⁶⁺ concentrations. 【Conclusion】 The selenium contents in leaves of sweet cherry were improved by exogenous selenium treatment, especially the Se⁶⁺ treatment. And selenium treatments affected the leaves melatonin contents and the efficiency of GSH redox cycle.

Key words: sweet cherry, selenium, melatonin, glutathione redox cycle