Enhanced anthocyanin accumulation of immature radish microgreens by hydrogen-rich water under short wavelength light

Hydrogen gas (H-2) is the most abundant chemical element in the universe, which has emerged recently as a novel beneficial gaseous molecule. Hydrogen-rich water (HRW) was used to investigate the effects of H-2 on growth, anthocyanin accumulation, as well as the antioxidant capacity of immature radish microgreens cultured under different light spectra, such as white, blue, ultraviolet-A (UV-A), as well as the darkness. The results showed that HRW significantly reversed UV-A-induced hypocotyl growth inhibition and overproduction of thiobarbituric acid-reactive substances (TBARS), compared to the white light control. The total phenolic content of immature radish microgreens grown under blue light + HRW and UV-A + HRW treatment were 1.12 and 1.17 times, respectively, higher than that of blue light and UV-A treatment alone. Four anthocyanin compounds were detected in immature radish microgreens. Under blue light + HRW treatment, the content of cyanidin and petunidin-3,5-diglucoside of immature radish microgreens was 1.50- and 1.35-fold greater than that of the blue light treatment, respectively. Under UV-A + HRW treatment, the content of cyanidin-3-rutinoside-5-glucoside and cyanidin-3-glucoside was 1.09- and 1.27-fold greater than that of the UV-A treatment, respectively. These trends were closely consistent with the transcriptional expression patterns of anthocyanin biosynthesis-related genes. Compared to the control, blue light and UV-A irradiation significantly promoted the enzyme activities of chalcone synthase (CHS) and UDP-glucose: flavonoid-O-glucosyltransferase (UFGT), and the promotion effects were substantially strengthened by co-treatment with HRW. The antioxidant capacity of immature microgreens increased with the anthocyanin content. These results indicate that HRW could be potentially applied to further enrich the anthocyanin content and antioxidant capacity of immature radish microgreens grown under short wavelength light.