Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel.
Max Planck Institute of Molecular Plant Physiology, D-14476 Potsdam-Golm, Germany.
J Exp Bot. 2017 Oct 13;68(17):4939-4950. doi: 10.1093/jxb/erx280.
The halotolerant green alga Dunaliella tertiolecta accumulates starch and triacylglycerol (TAG) amounting to 70% and 10-15% of total cellular carbon, respectively, when exposed to nitrogen (N) deprivation. The purpose of this study was to clarify the inter-relationships between the biosynthesis of TAG, starch, and polar lipids (PLs) in this alga. Pulse labeling with [14C]bicarbonate was utilized to label starch and [14C]palmitic acid (PlA) to label lipids. Transfer of 14C into TAG was measured and used to calculate rates of synthesis. About two-thirds of the carbon in TAG originates from starch, and one-third is made de novo by direct CO2 assimilation. The level made from degradation of pre-formed PLs is estimated to be very small. Most of the de novo synthesis involves fatty acid transfer through PLs made during the first day of N deprivation. The results suggest that starch made by photosynthetic carbon assimilation at the early stages of N deprivation is utilized for synthesis of TAG. Trans-acylation from PLs is the second major contributor to TAG biosynthesis. The utilization of starch for TAG biosynthesis may have biotechnological applications to optimize TAG biosynthesis in algae.
在氮饥饿条件下，耐盐绿藻杜氏盐藻分别积累淀粉和三酰基甘油(TAG)，其含量分别占总细胞碳的 70%和 10-15%。本研究旨在阐明该藻类中 TAG、淀粉和极性脂（PL）的生物合成之间的相互关系。利用[14C]碳酸氢盐脉冲标记来标记淀粉和[14C]棕榈酸（PlA）来标记脂质。测量 14C 向 TAG 的转移，并用于计算合成速率。TAG 中约三分之二的碳来源于淀粉，三分之一是通过直接 CO2 同化从头合成的。来自预先形成的 PL 降解的水平估计非常小。大部分从头合成涉及通过氮饥饿的第一天形成的 PL 中的脂肪酸转移。结果表明，在氮饥饿的早期阶段，通过光合作用同化的碳产生的淀粉用于 TAG 的合成。通过 PL 进行的反酰化是 TAG 生物合成的第二个主要来源。利用淀粉合成 TAG 可能具有生物技术应用，可优化藻类中的 TAG 生物合成。
