Energy status and its control on embryogenesis of legumes. Embryo photosynthesis contributes to oxygen supply and is coupled to biosynthetic fluxes
Energy status and its control on embryogenesis of legumes. Embryo photosynthesis contributes to oxygen supply and is coupled to biosynthetic fluxes
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DOI：
10.1104/pp.102.017376
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发表时间：
2003-07-01
期刊：
影响因子：
7.4
通讯作者：
Borisjuk, L
中科院分区：
文献类型：
--
作者：
Rolletschek, H;Weber, H;Borisjuk, L
豆科植物种子是异养的，依赖于线粒体呼吸。由于扩散气体交换有限，胚胎在低氧环境中生长。使用微传感器测量胚胎组织内的O-2水平，在早期阶段和夜间最低，高达0.4%的大气O-2浓度（1.1妈妈）。胚胎呼吸抑制较强烈的低O-2在早期比后期阶段。ATP含量和腺苷酸能荷在幼胚中最低，而乙醇释放和乙醇脱氢酶活性较高，表明ATP合成和发酵代谢受到限制。体外和体内实验进一步表明，胚胎代谢是O-2限制的。在成熟过程中，ATP水平增加，发酵代谢消失。这表明胚胎适应了低O-2，并能在更高水平上调节其能量状态。胚在分化过程中变为绿色并具有光合活性。光合作用的O-2生产提高了内部水平高达约50%的大气O-2浓度（135 μ M）。在光照条件下，胚分配约3倍以上的[C-14]蔗糖成淀粉。淀粉合成的光依赖性增加是发育调节的。然而，稳态水平的核苷酸，游离氨基酸，糖和糖酵解中间体没有改变后，光或黑暗条件。成熟的胚胎通过调节代谢通量而不是代谢物的稳态水平来响应低O-2供应。我们的结论是，胚发生光合作用增加生物合成通量可能通过提供O-2和能量，很容易用于生物合成和呼吸。
Legume seeds are heterotrophic and dependent on mitochondrial respiration. Due to the limited diffusional gas exchange, embryos grow in an environment of low oxygen. O-2 levels within embryo tissues were measured using microsensors and are lowest in early stages and during night, up to 0.4% of atmospheric O-2 concentration (1.1 mum). Embryo respiration was more strongly inhibited by low O-2 during earlier than later stages. ATP content and adenylate energy charge were lowest in young embryos, whereas ethanol emission and alcohol dehydrogenase activity were high, indicating restricted ATP synthesis and fermentative metabolism. In vitro and in vivo experiments further revealed that embryo metabolism is O-2 limited. During maturation, ATP levels increased and fermentative metabolism disappeared. This indicates that embryos become adapted to the low O-2 and can adjust its energy state on a higher level. Embryos become green and photosynthetically active during differentiation. Photosynthetic O-2 production elevated the internal level up to approximately 50% of atmospheric O-2 concentration (135 muM). Upon light conditions, embryos partitioned approximately 3-fold more [C-14]sucrose into starch. The light-dependent increase of starch synthesis was developmentally regulated. However, steady-state levels of nucleotides, free amino acids, sugars, and glycolytic intermediates did not change upon light or dark conditions. Maturing embryos responded to low O-2 supply by adjusting metabolic fluxes rather than the steady-state levels of metabolites. We conclude that embryogenic photosynthesis increases biosynthetic fluxes probably by providing O-2 and energy that is readily used for biosynthesis and respiration.