Producing High-Quality Buckwheat Sprouts: The Combined Effects of Melatonin and UV-B Treatment

Our prior research revealed that UV-B stress enhances bioactive compounds' biosynthesis in buckwheat sprouts while simultaneously increasing oxidative damage. To address this, we searched for an exogenous hormone capable of promoting bioactive compound accumulation while mitigating UV-B-induced oxidative damage. This study investigated the regulatory effects of exogenous melatonin (MT) on secondary metabolite accumulation and antioxidant systems in buckwheat sprouts under UV-B stress. MT (30 μM) treatment significantly increased the contents of bioactive compounds (flavonoids and total phenolics) in buckwheat sprouts under UV-B stress. Moreover, these contents peaked in 3-day-old sprouts, showing increases of 23.1% and 13.6%, respectively, compared to UV-B-treated. Concurrently, combined UV-B and MT treatment significantly elevated key enzyme activities in the phenylpropanoid pathway and upregulated the related gene expression levels. Additionally, exogenous MT significantly enhanced the antioxidant capacity of sprouts under 3-day UV-B stress, increasing DPPH radical scavenging rate and FRAP values by 8.38% and 12.2%, respectively. MT treatment also upregulated superoxide dismutase activity (32.1%), peroxidase activity (10.3%), and catalase activity (27.2%). It further enhanced the expression of antioxidant-related genes. Collectively, these effects reduced the accumulation of malondialdehyde, hydrogen peroxide, and superoxide anions, thereby mitigating UV-B-induced oxidative damage in sprouts. This research suggests a potential strategy for the targeted enhancement of bioactive compounds in buckwheat sprouts.