In photosynthetic cells, chloroplasts and mitochondria are the sites of the core redox reactions underpinning energy metabolism. Such reactions generate reactive oxygen species (ROS) when oxygen is partially reduced. ROS signaling leads to responses by cells which enable them to adjust to changes in redox status. Recent studies in Arabidopsis thaliana reveal that chloroplast NADH can be used to generate malate which is exported to the mitochondrion where its oxidation regenerates NADH. Oxidation of this NADH produces mitochondrial ROS (mROS) which can activate signaling systems to modulate energy metabolism, and in certain cases can lead to programmed cell death (PCD). We propose the term ‘malate circulation’ to describe such redistribution of reducing equivalents to mediate energy homeostasis in the cell.

在光合细胞中，叶绿体和线粒体是支撑能量代谢的核心氧化还原反应的位点。当氧被部分还原时，此类反应会生成活性氧（ROS）。ROS信号导致细胞做出反应，从而使其能够适应氧化还原状态的变化。最近在拟南芥中的研究表明，叶绿体NADH可用于产生苹果酸，然后将其输出到线粒体中，线粒体的氧化作用会再生NADH。该NADH的氧化产生线粒体ROS（mROS），它可以激活信号传导系统来调节能量代谢，在某些情况下会导致程序性细胞死亡（PCD）。我们提出术语“苹果酸循环”来描述还原当量的这种重新分布，以介导细胞中的能量稳态。