Differences of carotenoid composition in thallus and conchocelis of Neoporphyra haitanensis

Carotenoids are important photosynthetic pigments and antioxidants, which can regulate plant growth, development and environmental adaptation. In order to understand the responses of carotenoids in different growth stages Neoporphyra haitanensis, the compositions of carotenoids in conchocelis and thallus at different generations and harvest stages were analyzed by ultra-liquid chromatography-triple quadrupole mass spectrometry. The results showed that the optimal extraction conditions were as follows: methanol-dichloromethane (1∶1, V/V) as the extraction solvent, solid-to-liquid ratio 1∶10, and ultrasonic time 30 min. By optimizing the parameters of liquid chromatography, the resolution of 16 carotenoids reached 1.5, and the limit of detection was 1.57-4.96 ng/mL. A total of eight carotenoids were detected in two generations of N. haitanensis, belonging to α-carotene synthesis pathway (α-carotene, ε-carotene, α-cryptoxanthin and lutein) and 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. Among them, only the content of β-cryptoxanthin of conchocelis with stable growth state and low antioxidant requirements was 3.7 times higher than that of thallus, while the contents of α-carotene, β-carotene, ε-carotene, zeaxanthin, lutein and α-cryptoxanthin were 22.7%–67.0% of those of thallus. Zeaxanthin and lutein were the main carotenoids in the thallus. Except for β-carotene, the contents of the other seven carotenoids showed a downward trend with the extension of the harvest period. Studies showed that the content of carotenoids was closely related to growth stage and survival environment of N. haitanensis. To adapt to the strong light and high temperature stresses, carotenoids were synthesized rapidly in the early period of thallus to involve in stress defense and enhance its growth, while the synthesized rate of carotenoids in conchocelis and the late period of thallus were decreased for the weakened requirement of antioxidant. Hence, the results provided experimental data for further development of cultivars and seaweed farming.