Reduced mitochondrial malate dehydrogenase activity has a strong effect on photorespiratory metabolism as revealed by 13C labelling.
Reduced mitochondrial malate dehydrogenase activity has a strong effect on photorespiratory metabolism as revealed by 13C labelling.
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DOI：
10.1093/jxb/erw030
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发表时间：
2016-05
影响因子：
6.9
通讯作者：
Moritz T
中科院分区：
文献类型：
--
作者：
Lindén P;Keech O;Stenlund H;Gardeström P;Moritz T
使用定制的13C标记室，我们发现线粒体苹果酸脱氢酶活性降低影响光呼吸代谢。线粒体苹果酸脱氢酶（mMDH）在三羧酸（TCA）循环中催化苹果酸和草酰乙酸（OAA）的相互转化。它的活性对线粒体基质的氧化还原控制很重要，通过它可能参与TCA循环周转的调节。在拟南芥中，mMDH有两种亚型。在这里，我们研究了主要亚型mMDH1的缺乏在多大程度上影响了叶片代谢，mMDH1约占活性的60%。在空气中，mmdh1植株的莲座仅略小于野生型植株，但鲜重减少了约50%。在低二氧化碳环境下，差异更大，突变植株的鲜重积累仅为野生型的14%。为了研究生长差异的代谢背景，我们开发了一种13CO2标记方法，使用定制的室，可以在受控条件下同时处理多组植物。利用气相色谱、液相色谱和质谱联用分析了野生型和mmdh1之间的代谢变化。基因型对高CO2处理的代谢产物池和2小时处理期间13C掺入的反应相似。然而，在低CO2条件下，两种基因型的几种代谢物不同，有趣的是，其中大多数与光呼吸密切相关。我们发现，当甘氨酸/丝氨酸比值增加时，谷氨酰胺/谷氨酸/α-酮戊二酸关系也随之改变。综上所述，我们的研究结果表明，足够的mMDH活性对于将还原剂从线粒体输送出去以支持光呼吸通量至关重要，并加强了光呼吸与外周代谢反应紧密交织的观点。
Using a custom-built chamber for 13C labelling, we show that reduced mitochondrial malate dehydrogenase activity affects photorespiratory metabolism. Mitochondrial malate dehydrogenase (mMDH) catalyses the interconversion of malate and oxaloacetate (OAA) in the tricarboxylic acid (TCA) cycle. Its activity is important for redox control of the mitochondrial matrix, through which it may participate in regulation of TCA cycle turnover. In Arabidopsis, there are two isoforms of mMDH. Here, we investigated to which extent the lack of the major isoform, mMDH1 accounting for about 60% of the activity, affected leaf metabolism. In air, rosettes of mmdh1 plants were only slightly smaller than wild type plants although the fresh weight was decreased by about 50%. In low CO2 the difference was much bigger, with mutant plants accumulating only 14% of fresh weight as compared to wild type. To investigate the metabolic background to the differences in growth, we developed a 13CO2 labelling method, using a custom-built chamber that enabled simultaneous treatment of sets of plants under controlled conditions. The metabolic profiles were analysed by gas- and liquid- chromatography coupled to mass spectrometry to investigate the metabolic adjustments between wild type and mmdh1. The genotypes responded similarly to high CO2 treatment both with respect to metabolite pools and 13C incorporation during a 2-h treatment. However, under low CO2 several metabolites differed between the two genotypes and, interestingly most of these were closely associated with photorespiration. We found that while the glycine/serine ratio increased, a concomitant altered glutamine/glutamate/α-ketoglutarate relation occurred. Taken together, our results indicate that adequate mMDH activity is essential to shuttle reductants out from the mitochondria to support the photorespiratory flux, and strengthen the idea that photorespiration is tightly intertwined with peripheral metabolic reactions.