Loukanina Natalia, Stasolla Claudio, Belmonte Mark F, Yeung Edward C, Thorpe Trevor A
Plant Physiology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta, T2N 1N4, Canada.
Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, 3RT 2N2, Canada.
Plant Physiol Biochem. 2008 Jul;46(7):665-672. doi: 10.1016/j.plaphy.2007.10.017. Epub 2007 Oct 26.
Pyrimidine nucleotide metabolism was studied in tobacco callus cultured for 21days under shoot-forming (SF) and non-shoot-forming (NSF) conditions by following the metabolic fate of orotic acid, a precursor of the de novo pathway, and uridine and uracil, intermediates of the salvage and degradation pathways respectively. Nucleic acid synthesis was also investigated by measuring the incorporation of labeled thymidine into different cellular components. Our results indicate that with respect to nucleotide metabolism, the organogenic process in tobacco can be divided in two "metabolic phases": a de novo phase followed by a salvage phase. The initial stages of meristemoid formation during tobacco organogenesis (up to day 8) are characterized by a heavy utilization of orotic acid into nucleotides and nucleic acids. Utilization of this intermediate for the de novo synthesis of nucleotides, which is limited in NSF tissue, is mainly due to the activity of orotate phosphoribosyltransferase (OPRT), which increases in tissue cultured under SF conditions. After day 8, nucleotide synthesis during shoot growth seems to be mainly due to the salvage activity of both uridine and uracil. Both intermediates are preferentially utilized in SF tissue for the formation of nucleotides and nucleic acids through the activities of their respective salvage enzymes: uridine kinase (URK), and uracil phosphoribosyltransferase (UPRT). Metabolic studies on thymidine indicate that in SF tissue maximal nucleic acid synthesis occurs at day 4, in support of the initiation of meristemoid formation. Overall these results suggest that the organogenic process in tobacco is underlined by precise fluctuations in pyrimidine metabolism which delineate structural events culminating in shoot formation.
通过追踪乳清酸（从头合成途径的前体）、尿苷和尿嘧啶（分别为补救和降解途径的中间体）的代谢命运，研究了在形成芽（SF）和不形成芽（NSF）条件下培养21天的烟草愈伤组织中的嘧啶核苷酸代谢。还通过测量标记胸腺嘧啶核苷掺入不同细胞成分的情况来研究核酸合成。我们的结果表明，就核苷酸代谢而言，烟草中的器官发生过程可分为两个“代谢阶段”：从头合成阶段，随后是补救阶段。烟草器官发生过程中分生组织形成的初始阶段（直至第8天）的特征是大量利用乳清酸合成核苷酸和核酸。这种中间体用于核苷酸的从头合成，在NSF组织中受到限制，这主要是由于乳清酸磷酸核糖转移酶（OPRT）的活性，该酶在SF条件下培养的组织中增加。第8天后，芽生长过程中的核苷酸合成似乎主要归因于尿苷和尿嘧啶的补救活性。这两种中间体在SF组织中通过各自补救酶（尿苷激酶（URK）和尿嘧啶磷酸核糖转移酶（UPRT））的活性优先用于形成核苷酸和核酸。对胸腺嘧啶核苷的代谢研究表明，在SF组织中，最大核酸合成发生在第4天，这支持了分生组织形成的起始。总体而言，这些结果表明，烟草中的器官发生过程以嘧啶代谢的精确波动为基础，这些波动描绘了最终导致芽形成的结构事件。
