Exogenous melatonin affects the opening process of cut ‘Bartzella’ Itoh peony flowers

Melatonin is a type of indoleamine that is broadly spread in plants and can eliminate reactive oxygen species (ROS) by strengthening the function of the antioxidant system and enhancing the ability of plants to withstand adverse stress. Currently, melatonin is applied to cut flowers for postharvest storage. The effect of exogenous melatonin on the opening process of peony plants was studied by using ‘Bartzella’ Itoh peony cut flowers as the experimental material, deionized water as the control (CK) and 100 μmol L −1 melatonin solution as the treatment (MT). Contrary to previous findings, exogenous melatonin did not delay the vase life of ‘Bartzella’ Itoh peony, but several other interesting results were obtained. The opening process of cut flowers was divided into two stages. In the first stage, from the balloon stage to the full blooming stage Ⅰ, melatonin retarded the opening process. It not only maintained the water balance, elevated the fresh weight and the anthocyanin content, but also enhanced the ornamental quality. Moreover, it decreased the malondialdehyde (MDA) content, augmented the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and elevated the contents of soluble sugar and soluble protein. At this stage, melatonin postponed the opening process by alleviating water stress and peroxidation damage. In the second stage, from the full blooming stage II to the wilting stage, melatonin might accelerate the opening process. Exogenous melatonin modulated the synthesis and signal transduction of ethylene, promoted the sharp increase of ethylene production in the full blooming stage Ⅱ, thereby accelerating petal wilting and shedding. Nevertheless, regardless of the treatment, ethylene production exhibited typical climacteric behavior. The flower senescence of ‘Bartzella’ is regarded as an ethylene-dependent process. Although melatonin still retained a certain antioxidant capacity at this stage, the petals’ high responsiveness to ethylene led to rapid petal shedding. • The senescence of ‘Bartzella’ Itoh peony flowers is an ethylene-dependent process. • Melatonin delayed the opening process of cut flowers by reducing water stress and peroxidation damage. • Melatonin promoted ethylene production in the late stage of the cut-flower opening process.