Cultivar-specific responses of Brassica vegetables to UVA and UVB: Effects on secondary metabolites

Ultraviolet (UV) radiation is an important regulator of secondary metabolism in Brassica vegetables, yet species-specific responses to different UV wavebands remain insufficiently understood. We investigated how full-spectrum UV (+UV), UVA only (+UVA), and strongly UV-reduced (–UV) conditions affect pigments, phenolics, glucosinolates, and antioxidant activity in kale ( Brassica oleracea var. sabellica ) and pak choi ( Brassica rapa ssp. chinensis ). Biomass production was unaffected in both species. In kale, +UV enhanced chlorophylls, carotenoids, and flavonoid glycosides, resulting in the highest antioxidant capacity. Glucosinolate profiles responded divergently, with +UVA increasing total glucosinolates while +UV reduced them. Pak choi showed only modest UV effects on pigments and phenolics but clear modifications in specific aliphatic glucosinolates. These results reveal contrasting metabolic strategies in the two Brassica species and highlight the potential of wavelength-targeted lighting to selectively enhance nutritionally valuable metabolites in controlled-environment agriculture.