The Regulatory Role of Monochromatic LED Light Quality in β- Carotene Accumulation and Carbon Flow Allocation in Photosynthetic Pathways of Dunaliella salina

Abstract Dunaliella salina is a valuable source of natural metabolites, including lipids, proteins, glycerol, and carotenoids. However, the physiological mechanisms through which light quality regulates carbon allocation and biomass synthesis remain unclear. Here, a two-stage culture strategy was used to investigate the effects of white (WL), blue (BL), red (RL), and green light (GL) on algal growth, biochemical composition, photosynthetic performance, and the expression of key genes involved in biomass synthesis. BL promoted cell growth and the accumulation of photosynthetic pigments and proteins, yielding a maximum specific growth rate of 0.053 ± 0.002 d⁻¹ and a protein content of 381.86 ± 8.16 mg g⁻¹. Chlorophyll and carotenoid concentrations under BL reached 5.535 and 2.185 mg L⁻¹, respectively, exceeding those under the other treatments. These responses may be associated with enhanced photosynthetic electron transport, carbon assimilation, photosynthetic and respiratory activity, and reactive oxygen species-scavenging capacity. In contrast, RL produced the highest starch content (6.51 ± 0.10 mg g⁻¹), while WL and RL resulted in higher total lipid contents of 297.07 ± 2.59 and 288.98 ± 8.76 mg g⁻¹, respectively. Overall, light quality differentially affected growth and biochemical accumulation in D. salina . The increased starch and lipid accumulation under RL and WL may reflect oxidative-stress-associated adjustments in carbon allocation and adaptive cellular responses.