Responses of spinach leaf mitochondria to low N availability
Responses of spinach leaf mitochondria to low N availability
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DOI：
10.1111/j.1365-3040.2005.01457.x
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发表时间：
2006-04-01
影响因子：
7.3
通讯作者：
Terashima, I
中科院分区：
文献类型：
--
作者：
Noguchi, K;Terashima, I
低氮利用率会导致叶细胞中碳水化合物的积累，这通常会导致光合作用受到抑制。在低氮供应下，过量的碳水化合物会优先被非磷酸化途径呼吸，如替代氧化酶（AOX）和解偶联蛋白（UCP），从而抑制碳氮比（C/N比）的过度增加。然而，在叶子中，这些途径对低氮胁迫的反应仍然未知。我们检查了在三种不同氮利用率下生长的菠菜叶中的线粒体呼吸途径，以阐明呼吸途径是否根据氮利用率而变化。随着氮利用率的降低，每叶面积的叶片呼吸速率下降，但以叶片氮为基础的呼吸速率相当。利用全叶提取物和分离的线粒体的延胡索酶活性，我们估计了每叶N的线粒体蛋白含量。含量随着氮利用率的降低而增加，也就是说，在氮利用率较低时，氮优先投入线粒体。在线粒体蛋白基础上，无论氮利用率如何，细胞色素途径（CP）和细胞色素c氧化酶（COX）的容量都是相当的，而AOX容量和AOX蛋白的量都随着氮利用率的降低而增加。一些三羧酸（TCA）循环酶，特别是NAD依赖性苹果酸酶（NAD-ME），在较低的N条件下表现出较高的能力。另一方面，UCP的量在N可用性之间没有差异。这些结果表明，在低氮胁迫下，AOX会优先上调，并有效消耗多余的碳水化合物，从而将C/N比的上升抑制在适度水平。
Low N availability induces carbohydrate accumulation in leaf cells, which often causes suppression of photosynthesis. Under low N supply, excess carbohydrates would be preferentially respired by the non-phosphorylating pathways, such as the alternative oxidase (AOX) and uncoupling protein (UCP), which would suppress the excessive increase in the ratio of C to N (C/N ratio). In leaves, however, responses of these pathways to the low N stress are still unknown. We examined the mitochondrial respiratory pathways in spinach leaves grown at three different N availabilities to clarify whether the respiratory pathways change depending on the N availabilities. With the decrease in N availability, leaf respiratory rates per leaf area decreased, but the rates on the leaf N basis were comparable. Using fumarase activities of whole leaf extracts and isolated mitochondria, we estimated mitochondrial protein contents per leaf N. The contents increased with the decrease in the N availability, that is, at the low N availability, N was preferentially invested into mitochondria. On the mitochondrial protein basis, capacities of cytochrome pathway (CP) and cytochrome c oxidase (COX) were comparable regardless of the N availabilities, whereas both AOX capacity and the amounts of AOX protein increased with the decrease in the N availability. Some enzymes of tricarboxylic acid (TCA) cycle, especially NAD-dependent malic enzyme (NAD-ME), showed higher capacities under lower N. On the other hand, amounts of UCP did not differ amongst the N availabilities. These results indicated that, under low N stress, AOX will be preferentially up-regulated and will efficiently consume excess carbohydrates, which leads to suppressing the rise in the C/N ratio to a moderate level.