Effects of stepwise nitrogen depletion on carotenoid content, fluorescence parameters and the cellular stoichiometry of Chlorella vulgaris.
Stressful conditions can stimulate the accumulation of carotenoids in some microalgae. To obtain more knowledge of the stress response, we studied the effects of different N concentrations on unicellular content of carotenoids using Raman spectroscopic technique; cellular stoichiometric changes and the fluorescence parameters of Chlorella vulgaris were concomitantly studied. Initially, we optimized the Raman scattering conditions and demonstrated the feasibility of unicellular carotenoid analysis by Raman spectroscopic technique. The results showed that an integration time of 10 s, laser power at 0.1mW and an accumulation time of 1 were the optimum conditions, and the peak height at 1523cm-1scaled linearly with the carotenoid content in the range of 0.625-1440mg/L with a recovery rate of 97%~103%. In the experiment, seven different nitrogen levels ranging from 0 to 2.48×105μg/L were imposed. Samples were taken at the start, exponential phase and end of the experiment. The results showed that nitrogen stress can facilitate the synthesis of carotenoids, while at the same time, excessive nitrogen stress led to lower proliferative and photosynthetic activity. Compared with carotenoids, chlorophylls were more sensitive to nitrogen stress; it declined dramatically as stress processed. There existed no significant differences for Fv/Fm among different nitrogen levels during the exponential phase, while in the end, it declined and a significant difference appeared between cells in 2.48×105μg/L N and other experimental levels. Photosynthetic efficiency, namely the C/N mole ratio in algal cells, didnot significantly change during the exponential phase; however, apparent increases ultimately occurred, except for the stable C/N in BG11 medium. This increase matched well with the carotenoid decline, indicating that an increasing cellular C/N mole ratio can be used as an indicator of excessive stress in carotenoid production. Besides, there also existed an inverse correlation with ETRmax.
Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China.
Ping
P
Zhang
Key Laboratory of Reservoir Aquatic Environment of CAS, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714,China. Electronic address: Lizhe@cigit.ac.cn.
Zhe
Z
Li
Key Laboratory of Reservoir Aquatic Environment of CAS, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714,China.
Lunhui
L
Lu
Key Laboratory of Reservoir Aquatic Environment of CAS, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714,China.
Yan
Y
Xiao
Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China.
Jing
J
Liu
Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China; Key Laboratory of Reservoir Aquatic Environment of CAS, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714,China.
Jinsong
J
Guo
Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China.
Fang
F
Fang
D002338:Carotenoids / Q000032:analysis / Q000378:metabolism*; D048408:Chlorella vulgaris / Q000737:chemistry / Q000378:metabolism*; D016014:Linear Models; D058086:Microalgae / Q000737:chemistry / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D013059:Spectrum Analysis, Raman
D009566:Nitrates; D002338:Carotenoids; D009584:Nitrogen
Carotenoids; Cellular stoichiometry; Chlorella vulgaris; Nitrogen stress; Raman spectroscopy