Differences of carotenoid composition in thallus and conchocelis of Neoporphyra haitanensis

Carotenoids, essential photosynthetic pigments and antioxidants, regulate plant growth, development and environmental adaptation. This study aimed to elucidate the carotenoid responses in Neoporphyra haitanensis at different growth stages by analyzing carotenoid compositions in conchocelis and thallus across various generations and harvest stages using ultra-liquid chromatography-triple quadrupole mass spectrometry. Optimal extraction conditions were determined as methanol-dichloromethane (1∶1, V/V) as the solvent, a solid-to-liquid ratio 1∶10, and a 30 min ultrasonic time. Liquid chromatography parameters were optimized to achieve a resolution of 1.5 for 16 carotenoids, with a detection limit of 1.57-4.96 ng/mL. Eight carotenoids were detected in two generations of N. haitanensis, associated with the α-carotene synthesis pathway (α-carotene, ε-carotene, α-cryptoxanthin and lutein) and the β-carotene synthesis pathway (β-carotene, β-cryptoxanthin, zeaxanthin and antherxanthin). The total carotenoid content and the photochemical efficiency (F_v/F_m) in the thallus were 1.4- and 1.5-fold higher, respectively, than in the conchocelis. Notably, β-cryptoxanthin content in conchocelis, which has a stable growth state and low antioxidant requirements, was 3.7 times higher than thallus, while the contents of α-carotene, β-carotene, ε-carotene, zeaxanthin, lutein and α-cryptoxanthin were 22.7%-67.0% of those in the thallus. Zeaxanthin and lutein were the predominant carotenoids in the thallus. Except for β-carotene, the contents of the other seven carotenoids decreased with the extension of the harvest period. The study indicates that carotenoid content is closely related to the growth stage and survival environment of N. haitanensis. Rapid carotenoid synthesis in the early thallus period is likely a response to strong light and high temperature stresses, facilitating stress defense and growth. Conversely, a decreased synthesis rate in conchocelis and the late thallus period suggests a reduced antioxidant requirement. These findings provide valuable experimental data for further development of cultivars and seaweed farming practices.