Effect of Supplemental UV-A Intensity on Growth and Quality of Kale under Red and Blue Light

Different intensities of UV-A (6, 12, 18 μmol·m^-2s^-1) were applied in a plant factory to evaluate the combined influences of supplemental UV-A and red and blue light (Red:Blue = 1:1 at PPFD of 250 μmol·m^-2 s^-1) on the biomass, antioxidant activity and phytochemical accumulation of kale. Supplemental UV-A treatments (T1: 6 μmol·m^-2 s^-1, T2: 12 μmol·m^-2 s^-1 and T3: 18 μmol·m^-2 s^-1) resulted in higher moisture content, higher pigment content, and greater leaf area of kale while T2 reached its highest point. T2 treatment positively enhanced the antioxidant capacity, increased the contents of soluble protein, soluble sugar and reduced the nitrate content. T1 treatment markedly increased the content of aliphatic glucosinolate (GSL), whereas T2 treatment highly increased the contents of indolic GSL and total GSL. Genes related to GSL biosynthesis were down-regulated in CK and T3 treatments, while a majority of them were greatly up-regulated by T1 and T2. Hence, supplemental 12 μmol·m^-2 s^-1 UV-A might be a promising strategy to enhance the growth and quality of kale in a plant factory.