Abiotic stress not only elevates the synthesis of secondary metabolites in plant sprouts but also boosts their antioxidant capacity. In this study, the mechanisms of flavonoid biosynthesis and antioxidant systems in buckwheat sprouts exposed to ultraviolet-B (UV-B) radiation were investigated. The findings revealed that UV-B treatment significantly increased flavonoid content in buckwheat sprouts, with 3-day-old sprouts exhibiting a flavonoid content 1.73 times greater than that of the control treatment. UV-B radiation significantly increased the activities of key enzymes involved in flavonoid biosynthesis (phenylalanine ammonia-lyase, 4-coumarate-CoA ligase, cinnamate 4-hydroxylase, and chalcone synthase) and the relative expression levels of the corresponding genes. Although UV-B radiation caused damage to the cell membranes of buckwheat sprouts, promoting increases in hydrogen peroxide and malondialdehyde content and inhibiting the growth of sprouts, importantly, UV-B radiation also significantly increased the activities of catalase, peroxidase, and superoxide dismutase as well as the relative expression levels of the corresponding genes, thus enhancing the antioxidant system of buckwheat sprouts. This enhancement was corroborated by a notable increase in ABTS, DPPH, and FRAP radical scavenging activities in 3-day-old sprouts subjected to UV-B radiation. Additionally, UV-B radiation significantly increased chlorophyll a and chlorophyll b contents in sprouts. These results suggest that UV-B radiation is advantageous for cultivating buckwheat sprouts with increased flavonoid content and enhanced antioxidant capacity.

Buckwheat possesses significant nutritional content and contains different bioactive compounds, such as total flavonoids, which enhance its appeal to consumers. This study employed single-factor experiments and the response surface methodology to identify the optimal germination conditions for enhancing the total flavonoid content in buckwheat sprouts through ultraviolet-B treatment. The research showed that buckwheat sprouts germinated for 3 days at a temperature of 28.7 °C while being exposed to ultraviolet-B radiation at an intensity of 30.0 μmol·m⁻²·s⁻¹ for 7.6 h per day during the germination period resulted in the highest total flavonoid content of 1872.84 μg/g fresh weight. Under these specified conditions, ultraviolet-B treatment significantly elevated the activity and gene expression levels of enzymes related to the phenylpropanoid metabolic pathway, including phenylalanine ammonia-lyase, cinnamic acid 4-hydroxylase, 4-coumarate coenzyme A ligase, and chalcone isomerase. Ultraviolet-B treatment caused oxidative damage to buckwheat sprouts and inhibited their growth, but ultraviolet-B treatment also enhanced the activity of key enzymes in the antioxidant system, such as catalase, peroxidase, superoxide dismutase, and ascorbate peroxidase. This research provided a technical reference and theoretical support for enhancing the isoflavone content in buckwheat sprouts through ultraviolet-B treatment.

In this research, we investigated the physiological modifications, flavonoid metabolism, and antioxidant systems of two buckwheat (Fagopyrum esculentum Moench.) cultivars, Pintian and Suqiao, during germination. The results demonstrated an initial increase followed by a subsequent decline in the flavonoid content of the buckwheat sprouts throughout germination. On the third day of germination, the highest flavonoid concentrations were observed, with the Pintian and Suqiao varieties reaching 996.75 and 833.98 μg/g fresh weight, respectively. Both the activity and relative gene expression level of the flavonoid metabolizing enzyme showed a significant rise in 3-day-old buckwheat sprouts, which was strongly correlated with the flavonoid content. The correlation analysis revealed that the buckwheat sprouts accumulated flavonoids by enhancing the activities and gene expression levels of flavonoid synthases. The antioxidant capacity and the activities and gene expression profiles of the antioxidant enzymes in both buckwheat cultivars notably increased after three days of germination. The correlation analysis indicated a significant positive link between antioxidant capacity and the activity and gene expression levels of the antioxidant enzymes, flavonoid content, and total phenol content. This research demonstrated that germination treatment can significantly boost the accumulation of flavonoids and total phenols, thereby enhancing the antioxidant properties of buckwheat sprouts, despite variations among different buckwheat varieties.

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.

Exposure to abiotic stresses commonly stimulates the production of secondary metabolites in plants, and flavonoids represent a major class of these bioactive compounds. NaCl effects on antioxidant system treatment and flavonoid production in buckwheat sprouts was examined in this study using buckwheat as the raw material. In order to clarify the regulatory function of NaCl in these physiological processes, the changes in pertinent indices of buckwheat sprouts exposed to the control and NaCl treatments were studied. The results indicated that at three days old, the sprouts subjected to 80 mM NaCl treatment exhibited the highest total flavonoid content. The significant increase in enzyme activity (cinnamate 4-hydroxylase and 4-coumaroyl-CoA ligase, etc.) responsible for flavonoid biosynthesis provides strong evidence for this conclusion. The antioxidant system in buckwheat was activated by NaCl treatment, as evidenced by the dramatically increased antioxidant enzyme activities and the relative levels of expression of their respective genes compared to the control group. Levels of malondialdehyde and hydrogen peroxide were markedly higher than those in the control group, indicating that NaCl treatment inhibited the growth of buckwheat sprouts. This study not only reveals the mechanisms underlying buckwheat’s response to NaCl stress but also lays a theoretical foundation for developing functional foods enriched with flavonoid-rich buckwheat sprouts.