Jayawardhane Jayamini, Cochrane Devin W, Vyas Poorva, Bykova Natalia V, Vanlerberghe Greg C, Igamberdiev Abir U
Department of Biology, Memorial University of Newfoundland, St. John's, NL, Canada.
Morden Research and Development Centre, Agriculture and Agri-Food Canada, Morden, MB, Canada.
Front Plant Sci. 2020 May 15;11:566. doi: 10.3389/fpls.2020.00566. eCollection 2020.
Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain (ETC) that has a lower affinity for oxygen than does cytochrome (cyt) oxidase. To investigate the role(s) of AOX under different oxygen conditions, wild-type (WT) plants were compared with AOX knockdown and overexpression plants under normoxia, hypoxia (near-anoxia), and during a reoxygenation period following hypoxia. Paradoxically, under all the conditions tested, the AOX amount across plant lines correlated positively with leaf energy status (ATP/ADP ratio). Under normoxia, AOX was important to maintain respiratory carbon flow, to prevent the mitochondrial generation of superoxide and nitric oxide (NO), to control lipid peroxidation and protein -nitrosylation, and possibly to reduce the inhibition of cyt oxidase by NO. Under hypoxia, AOX was again important in preventing superoxide generation and lipid peroxidation, but now contributed positively to NO amount. This may indicate an ability of AOX to generate NO under hypoxia, similar to the nitrite reductase activity of cyt oxidase under hypoxia. Alternatively, it may indicate that AOX activity simply reduces the amount of superoxide scavenging of NO, by reducing the availability of superoxide. The amount of inactivation of mitochondrial aconitase during hypoxia was also dependent upon AOX amount, perhaps through its effects on NO amount, and this influenced carbon flow under hypoxia. Finally, AOX was particularly important in preventing nitro-oxidative stress during the reoxygenation period, thereby contributing positively to the recovery of energy status following hypoxia. Overall, the results suggest that AOX plays a beneficial role in low oxygen metabolism, despite its lower affinity for oxygen than cytochrome oxidase.
交替氧化酶（AOX）是植物线粒体电子传递链（ETC）中一种不进行能量守恒的末端氧化酶，它对氧气的亲和力低于细胞色素（cyt）氧化酶。为了研究AOX在不同氧气条件下的作用，将野生型（WT）植物与AOX基因敲低和过表达的植物在常氧、低氧（接近无氧）以及低氧后的复氧期进行了比较。矛盾的是，在所有测试条件下，不同株系植物中的AOX含量与叶片能量状态（ATP/ADP比值）呈正相关。在常氧条件下，AOX对于维持呼吸碳流、防止线粒体产生超氧化物和一氧化氮（NO）、控制脂质过氧化和蛋白质亚硝化作用很重要，并且可能有助于减少NO对细胞色素氧化酶的抑制。在低氧条件下，AOX在防止超氧化物生成和脂质过氧化方面同样重要，但此时对NO含量有正向贡献。这可能表明AOX在低氧条件下具有产生NO的能力，类似于细胞色素氧化酶在低氧条件下的亚硝酸还原酶活性。或者，这可能表明AOX活性只是通过减少超氧化物的可利用性来降低NO清除超氧化物的量。低氧期间线粒体乌头酸酶的失活程度也取决于AOX的含量，这可能是通过其对NO含量的影响实现的，并且这影响了低氧条件下的碳流。最后，AOX在防止复氧期的硝基氧化应激方面特别重要，从而对低氧后能量状态的恢复有正向贡献。总体而言，结果表明AOX在低氧代谢中发挥有益作用，尽管其对氧气的亲和力低于细胞色素氧化酶。
