Effects of Nitrogen Limitation on Biochemical Composition and Photosynthetic Physiology during Lipid Accumulation in Chlorella vulgaris Beijierineck
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摘要: 以产油普通小球藻 (Chlorella vulgaris Beijierineck)为材料,通过设置不同的初始硝酸钠浓度,研究不同程度的氮素限制对普通小球藻生长、生化组成及光合生理的影响。结果显示,在实验设置的4个氮素浓度下(18.0、9.0、4.5、3.6 mmol/L),普通小球藻生物量无显著差异,但较低的初始氮浓度明显促进了其油脂积累,其中4.5 mmol/L组藻细胞的总脂含量和总脂产率最高,分别达到干重的48.32%及0.0931 g·L-1·d-1,显著高于18.0 mmol/L的正常氮组 (P<0.05)。4个氮浓度组藻细胞内碳水化合物及可溶性蛋白的含量均有下降,油脂积累量逐渐升高,2个低氮组 (4.5 mmol/L和3.6 mmol/L) 在培养初期藻细胞内可溶性蛋白大量降解,油脂及碳水化合物有所积累,但碳水化合物随后逐渐转化为油脂。PSⅡ最大光能转化效率 (Fv/Fm)、实际光能转化效率 (Yield) 以及相对电子传递效率 (ETR) 在培养过程中均呈下降趋势,77 K低温荧光结果显示,培养初期,2个光系统之间存在光能调配和状态转化。代表固碳能力的Rubisco活性表现为在较高氮浓度组先上升后下降,而在2个低氮组呈下降趋势;4个氮浓度组Rubisco的活化程度均呈先下降后上升的趋势。该研究表明适宜氮素限制促进普通小球藻油脂积累的过程中碳素分配和光合生理存在协同调控。Abstract: Microalgae of the genus Chlorella are capable of accumulating lipids when exposed to nutrient limitation (especially nitrogen) and are therefore considered promising organisms for biodiesel production. This study explored the effects of nitrogen limitation on biomass, biochemical components and photosynthetic physiological parameters of C.vulgaris Beijierineck, an oleaginous microalga. Growth experiments were carried out in modified BG-11 medium with four different initial concentrations of sodium nitrate (18.0, 9.0, 4.5 and 3.6 mmol/L). These four nitrogen concentrations had no remarkable influence on growth, but exerted considerable influence on lipid accumulation in C. vulgaris. Maximum lipid content and productivity were obtained in the 4.5 mmol/L group (48.32% of dry weight and 0.0931 g·L-1·d-1, respectively), which increased significantly (P<0.05) compared with those of the 18.0 mmol/L group. The content of carbohydrate and soluble protein in the four groups decreased with increased lipid accumulation; however, in the low nitrogen groups (4.5 mmol/L and 3.6 mmol/L), the soluble protein degraded rapidly for carbohydrate synthesis at the initial stage, but the accumulated carbohydrate at the initial stage eventually converted to lipid at the later stage of cultivation. The maximum efficiency of light energy conversion of PSⅡ (Fv/Fm), actual energy conversion efficiency (Yield), and relative electron transfer efficiency (ETR) all decreased significantly, and the change in F683/F718 suggested optical energy distribution and state transition between PSⅠ and PSⅡ. In addition, the initial and total Rubisco activity of C. vulgaris in the 18.0 mmol/L and 9.0 mmol/L groups both peaked on the third day and then declined, while the Rubisco activity in the low nitrogen groups declined constantly. The ratio of initial and total Rubisco activity tended to decline at first and then increase. In conclusion, nitrogen limitation promoted lipid accumulation in C. vulgaris, and carbon distribution and photosynthetic physiology changed markedly.
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