背景回顾：Proline (Pro) catabolism and reactive oxygen species production have been linked in mammals and Caenorhabditis elegans, while increases in leaf respiration rate follow Pro exposure in plants. 

主要研究：Here we investigated how alternative oxidases (AOXs) of the mitochondrial electron transport chain accommodate the large, atypical flux resulting from Pro catabolism and limit oxidative stress during Pro breakdown in mature Arabidopsis (Arabidopsis thaliana) leaves. 

结果1-诱导表达：Following Pro treatment, AOX1a and AOX1d accumulate at transcript and protein levels, with AOX1d approaching the level of the typically dominant AOX1a isoform. We therefore sought to determine the function of both AOX isoforms under Pro respiring conditions. 

结果2-Pro处理单突表型：Oxygen consumption rate measurements in aox1a and aox1d leaves suggested these AOXs can functionally compensate for each other to establish enhanced AOX catalytic capacity in response to Pro. 

结果3-Pro处理双突表型：Generation of aox1a.aox1d lines showed complete loss of AOX proteins and activity upon Pro treatment, yet full respiratory induction in response to Pro remained possible via the cytochrome pathway. However, aox1a.aox1dleaves displayed symptoms of elevated oxidative stress and suffered increased oxidative damage during Pro metabolism compared to the WT or the single mutants. 

结果4-盐胁迫后恢复：During recovery from salt stress, when relatively high rates of Pro catabolismoccur naturally, photosynthetic rates in aox1a.aox1d recovered slower than in WT or the single aoxlines, showing that both AOX1a and AOX1d are beneficial for cellular metabolism during Pro drawdown following osmotic stress. 

结论：This work provides physiological evidence of a beneficial role for AOX1a but also the less studied AOX1d isoform in allowing safe catabolism of alternative respiratory substrates like Pro.

 摘 要 

在哺乳动物和线虫中，脯氨酸分解代谢往往与活性氧物质的生成是关联的，而在植物中，通过外源的脯氨酸处理往往会增加叶片的呼吸速率。本文中，作者研究了线粒体电子传递链上的交替氧化酶AOXs如何在成熟拟南芥叶片脯氨酸衰减过程中，解决由脯氨酸分解代谢所产生的大量、非典型的，并限制氧化应激胁迫。在脯氨酸处理后，AOX1a和AOX1d的转录和蛋白水平都有所提升，其中AOX1d也达到了平时占主要地位的AOX1a异构体的水平。因此，作者进一步研究了脯氨酸处理促进呼吸的情况下，这两个AOX1异构体的功能。aox1a和aox1d突变体叶片的耗氧率检测显示这两个AOXs能够在功能上互补，在响应脯氨酸的情况下赠强AOX催化能力。aox1a aox1d双突植株显示AOX蛋白的功能和活性在脯氨酸处理时完全缺失，但通过细胞色素途径对响应脯氨酸的完全呼吸诱导仍然是可能的。但是， 在脯氨酸代谢过程中相比于野生型或者单突植株，aox1a aox1d双突的叶片表现出氧化应激胁迫提升的症状，并且遭受了更多的氧化应激损伤。在盐胁迫后的恢复阶段，植株体内会自然发生相对高水平的脯氨酸分解代谢过程，aox1a aox1d双突植株的光合速率恢复是要比野生型或者aox单突株系慢的，表明AOX1a和AOX1d对于渗透胁迫后脯氨酸含量降低所发生的细胞代谢是非常有益的。本文的研究揭示了AOX1a以及平时研究的较少的AOX1d参与了植物中脯氨酸等另类呼吸底物的安全分解代谢过程。