University of California, Davis Genome Center, Davis, California 95616, USA.
Mol Cell Proteomics. 2012 Oct;11(10):973-88. doi: 10.1074/mcp.M111.016733. Epub 2012 Jul 10.
Drastic alterations in macronutrients are known to cause large changes in biochemistry and gene expression in the photosynthetic alga Chlamydomonas reinhardtii. However, metabolomic and proteomic responses to subtle reductions in macronutrients have not yet been studied. When ammonium levels were reduced by 25-100% compared with control cultures, ammonium uptake and growth rates were not affected at 25% or 50% nitrogen-reduction for 28 h. However, primary metabolism and enzyme expression showed remarkable changes at acute conditions (4 h and 10 h after ammonium reduction) compared with chronic conditions (18 h and 28 h time points). Responses of 145 identified metabolites were quantified using gas chromatography-time of flight mass spectrometry; 495 proteins (including 187 enzymes) were monitored using liquid chromatography-ion trap mass spectrometry with label-free spectral counting. Stress response and carbon assimilation processes (Calvin cycle, acetate uptake and chlorophyll biosynthesis) were altered first, in addition to increase in enzyme contents for lipid biosynthesis and accumulation of short chain free fatty acids. Nitrogen/carbon balance metabolism was found changed only under chronic conditions, for example in the citric acid cycle and amino acid metabolism. Metabolism in Chlamydomonas readily responds to total available media nitrogen with temporal increases in short-chain free fatty acids and turnover of internal proteins, long before nitrogen resources are depleted.
大量研究表明，宏量营养素的剧烈变化会引起光合作用藻类莱茵衣藻的生物化学和基因表达的巨大变化。然而，目前还没有研究过微量减少宏量营养素对其代谢组学和蛋白质组学的响应。与对照培养物相比，当铵水平降低 25%-100%时，在 25%或 50%氮还原的 28 小时内，铵吸收和生长速率不受影响。然而，与慢性条件（18 小时和 28 小时时间点）相比，在急性条件（铵还原后 4 小时和 10 小时）下，初级代谢和酶表达显示出显著的变化。使用气相色谱-飞行时间质谱定量测定了 145 种鉴定代谢物的响应；使用带有无标记光谱计数的液相色谱-离子阱质谱监测了 495 种蛋白质（包括 187 种酶）。除了增加脂质生物合成和短链游离脂肪酸积累的酶含量外，应激反应和碳同化过程（卡尔文循环、乙酸盐摄取和叶绿素生物合成）首先发生改变。只有在慢性条件下才发现氮/碳平衡代谢发生变化，例如在柠檬酸循环和氨基酸代谢中。衣藻的代谢可以很容易地对总可用培养基氮做出响应，在氮资源耗尽之前，短链游离脂肪酸的含量会暂时增加，内部蛋白质的周转率也会增加。
