Effects of monochromatic LED light qualities on the photosynthetic capacity and pigment content of Dunaliella salina

Abstract Light quality is a crucial abiotic environmental factor that influences the growth and β-carotene accumulation on Dunaliella salina. However, the influence of the factor on the primary photochemical reactions of D. salina and the physiological mechanisms regulating β-carotene metabolism remains unclear at present. This study involved the batch culture of D. salina using low light (40 ± 5 μmol photons m-2 s-1, without inhibiting photosynthetic electron transfer) provided by different colored LEDs. Our results indicated that the growth rate, chlorophyll a/chlorophyll b/β-carotene content of D. salina cells were higher under BL and RL than under WL and GL. The light absorption rates of chloroplasts in algae cells under BL and RL (22.8% and 18.6%, respectively) were higher than those under WL and GL (14.0% and 10.2%, respectively), which was attributed to the reduced light energy dissipation and increased photochemical efficiency under BL and RL. BL and RL enhanced the photosynthetic efficiency and β-carotene synthesis capability of D. salina cells. It was observed that under low light, light quality has little influence on the synthesis process of β-carotene. However, two key genes involved in the degradation pathway of β-carotene (LUT5 and ABA2) are significantly downregulated under both BL and RL. The higher content of all-trans β-carotene under BL than under RL. This is attributed to the inhibition of the conversion pathway from all-trans β-carotene to ABA biosynthesis precursor (9-cis-β-carotene) is more pronounced under BL than under RL. This explains why D.salina has a higher content of all-trans β-carotene under BL, while synthesized more 9-cis-β-carotene under RL.