Accumulation of carotenoids in Brassica rapa ssp. chinensis by a high proportion of blue in the light spectrum

Carotenoids have the potential to improve the human health which leads to an increasing consumer demand for carotenoid-rich vegetables. The implementation of new, less energy-consuming vegetable production systems using artificial light such as light-emitting diodes (LEDs) is essential. In the present study, pak choi (Brassica rapa ssp. chinensis 'Black Behi') sprouts were grown under a combination of blue and white LEDs, red and white LEDs or only white LEDs for 7 days. Total carotenoid levels of ~ 700 ng/mg DM were measured under white LEDs. The combination of blue and white LEDs increased the carotenoid levels by ~ 15% in comparison to only white LEDs, while red and white LEDs reduced them. The transcript levels of important carotenoid metabolism-related genes were enhanced under blue and white LEDs. Phytoene measurement after Norflurazon-treatment, a phytoene desaturase inhibitor, revealed that phytoene increased by 38% (37.5 µM Norflurazon) and by 56% (50.0 µM Norflurazon) after growth under blue and white LEDs in comparison to only white LEDs suggesting an up-regulation of the upper carotenoid biosynthetic pathway. Thus, the transcript levels and the enhanced phytoene levels correlated well with the higher accumulation of carotenoids under blue and white LEDs. Furthermore, a comparison to sprouts grown under blue LEDs without additional white LEDs showed that blue light alone does not increase the phytoene levels after Norflurazon-treatment. Overall, this study demonstrated a beneficial effect of a higher blue light percentage in growing carotenoid-rich pak choi sprouts, and implies that an increased biosynthesis within the upper carotenoid biosynthetic pathway is responsible for the enhanced carotenoid accumulation.