The Relationship of Triacylglycerol and Starch Accumulation to Carbon and Energy Flows during Nutrient Deprivation in Chlamydomonas reinhardtii
The Relationship of Triacylglycerol and Starch Accumulation to Carbon and Energy Flows during Nutrient Deprivation in Chlamydomonas reinhardtii
复制标题
DOI：
10.1104/pp.16.00761
复制
发表时间：
2016-08-01
期刊：
影响因子：
7.4
通讯作者：
Shachar-Hill, Yair
中科院分区：
文献类型：
--
作者：
Juergens, Matthew T.;Disbrow, Bradley;Shachar-Hill, Yair
由于藻类对绿色生物技术的潜在重要性，人们已经投入了相当大的努力来了解它们对氮剥夺的反应。三酰甘油(TAG)和淀粉积累在细胞内的最常见原因可能是所谓的“溢出假说”的变体。根据这一点，生长抑制会导致光合作用能量和/或碳输入的速率超过细胞所需；多余的输入被引导到TAG和/或淀粉的积累，以防止损害。这项研究的目的是提供一个量化的数据集，并在一个模型系统中对缺氮之前和期间的主要能量和碳流进行分析，以评估替代解释。记录了9种不同自养、混养和异养条件下培养的莱茵衣藻细胞在营养充分生长期间和缺氮前4d的细胞生长、生物量、淀粉和脂肪水平以及几项光合作用功能指标。C-13标记时间过程的结果表明，在混合营养培养中，淀粉主要由CO2合成，脂肪酸的合成主要由外源醋酸酯提供，膜脂有相当大的周转率，因此总脂而不是TAG是衡量产物积累的合适指标。异养培养在缺氮过程中积累了TAG和淀粉，表明它们不依赖于光合作用。我们的结论是，溢出假说是不充分的，并表明在营养剥夺期间，储存可能是碳化合物积累的更普遍的重要原因。
Because of the potential importance of algae for green biotechnology, considerable effort has been invested in understanding their responses to nitrogen deprivation. The most frequently invoked reasons proposed for the accumulation of high cellular levels of triacylglycerol (TAG) and starch are variants of what may be termed the "overflow hypothesis." According to this, growth inhibition results in the rate of photosynthetic energy and/or carbon input exceeding cellular needs; the excess input is directed into the accumulation of TAG and/or starch to prevent damage. This study was aimed at providing a quantitative dataset and analysis of the main energy and carbon flows before and during nitrogen deprivation in a model system to assess alternative explanations. Cellular growth, biomass, starch, and lipid levels as well as several measures of photosynthetic function were recorded for cells of Chlamydomonas reinhardtii cultured under nine different autotrophic, mixotrophic, and heterotrophic conditions during nutrient-replete growth and for the first 4 d of nitrogen deprivation. The results of a C-13 labeling time course indicated that in mixotrophic culture, starch is predominantly made from CO2 and fatty acid synthesis is largely supplied by exogenous acetate, with considerable turnover of membrane lipids, so that total lipid rather than TAG is the appropriate measure of product accumulation. Heterotrophic cultures accumulated TAG and starch during N deprivation, showing that these are not dependent on photosynthesis. We conclude that the overflow hypothesis is insufficient and suggest that storage may be a more universally important reason for carbon compound accumulation during nutrient deprivation.