Santelia Diana, Trost Paolo, Sparla Francesca
Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
Department of Pharmacy and Biotechnology FaBiT, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy.
Curr Opin Plant Biol. 2015 Jun;25:1-9. doi: 10.1016/j.pbi.2015.04.003. Epub 2015 Apr 19.
Starch is one of the major sinks of fixed carbon in photosynthetic tissues of higher plants. Carbon fixation and the synthesis of primary starch occur during the day in the chloroplast stroma, whereas starch degradation typically occurs during the following night to fuel the whole plant with energy and carbon in the absence of photosynthesis. Redox-based regulatory systems play a central role in the modulation of several chloroplastic pathways. Reversible oxidations of cysteine residues are post-translational modifications that orchestrate the precise functioning of chloroplast pathways together with changes in pH, Mg(2+) and concentrations of metabolic intermediates. Leaf starch metabolism has been intensively studied. The enzymes involved in starch synthesis and degradation have been identified and characterized. However, the redox control of the enzymes responsible for starch degradation at night remains elusive, and their response to redox transitions conflicts with the timing of the physiological events. Most of the enzymes of starch degradation are activated by reducing conditions, characteristic of daytime. Thus, redox control may have only a minor role during starch degradation at night, but could become relevant for daily stomatal opening in guard cells or in the re-allocation of fixed carbon in mesophyll cells in response to stress conditions.
淀粉是高等植物光合组织中固定碳的主要库之一。碳固定和初级淀粉的合成在白天叶绿体基质中进行，而淀粉降解通常在随后的夜晚发生，以便在没有光合作用的情况下为整个植物提供能量和碳。基于氧化还原的调节系统在调控多个叶绿体途径中起核心作用。半胱氨酸残基的可逆氧化是一种翻译后修饰，它与pH、Mg(2+)和代谢中间体浓度的变化一起协调叶绿体途径的精确运作。叶片淀粉代谢已得到深入研究。参与淀粉合成和降解的酶已被鉴定和表征。然而，夜间负责淀粉降解的酶的氧化还原控制仍然不清楚，并且它们对氧化还原转变的反应与生理事件的时间不一致。淀粉降解的大多数酶在还原条件下被激活，这是白天的特征。因此，氧化还原控制在夜间淀粉降解过程中可能只起次要作用，但可能与保卫细胞中气孔的日常开放或叶肉细胞中固定碳在应激条件下的重新分配有关。
