Vishwakarma Abhaypratap, Tetali Sarada Devi, Selinski Jennifer, Scheibe Renate, Padmasree Kollipara
Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India.
Department of Plant Physiology, FB5, University of Osnabrück, 49069 Osnabrück, Germany and.
Ann Bot. 2015 Sep;116(4):555-69. doi: 10.1093/aob/mcv122. Epub 2015 Aug 20.
The importance of the alternative oxidase (AOX) pathway, particularly AOX1A, in optimizing photosynthesis during de-etiolation, under elevated CO2, low temperature, high light or combined light and drought stress is well documented. In the present study, the role of AOX1A in optimizing photosynthesis was investigated when electron transport through the cytochrome c oxidase (COX) pathway was restricted at complex III.
Leaf discs of wild-type (WT) and aox1a knock-out mutants of Arabidopsis thaliana were treated with antimycin A (AA) under growth-light conditions. To identify the impact of AOX1A deficiency in optimizing photosynthesis, respiratory O2 uptake and photosynthesis-related parameters were measured along with changes in redox couples, reactive oxygen species (ROS), lipid peroxidation and expression levels of genes related to respiration, the malate valve and the antioxidative system.
In the absence of AA, aox1a knock-out mutants did not show any difference in physiological, biochemical or molecular parameters compared with WT. However, after AA treatment, aox1a plants showed a significant reduction in both respiratory O2 uptake and NaHCO3-dependent O2 evolution. Chlorophyll fluorescence and P700 studies revealed that in contrast to WT, aox1a knock-out plants were incapable of maintaining electron flow in the chloroplastic electron transport chain, and thereby inefficient heat dissipation (low non-photochemical quenching) was observed. Furthermore, aox1a mutants exhibited significant disturbances in cellular redox couples of NAD(P)H and ascorbate (Asc) and consequently accumulation of ROS and malondialdehyde (MDA) content. By contrast, WT plants showed a significant increase in transcript levels of CSD1, CAT1, sAPX, COX15 and AOX1A in contrast to aox1a mutants.
These results suggest that AOX1A plays a significant role in sustaining the chloroplastic redox state and energization to optimize photosynthesis by regulating cellular redox homeostasis and ROS generation when electron transport through the COX pathway is disturbed at complex III.
替代氧化酶（AOX）途径，尤其是AOX1A，在去黄化过程中、高二氧化碳浓度、低温、高光或光与干旱胁迫组合条件下优化光合作用的重要性已有充分记载。在本研究中，当通过细胞色素c氧化酶（COX）途径的电子传递在复合体III处受到限制时，研究了AOX1A在优化光合作用中的作用。
在生长光照条件下，用抗霉素A（AA）处理拟南芥野生型（WT）和aox1a基因敲除突变体的叶圆片。为了确定AOX1A缺陷对优化光合作用的影响，测量了呼吸氧气吸收和光合作用相关参数，以及氧化还原对、活性氧（ROS）、脂质过氧化的变化，以及与呼吸、苹果酸阀和抗氧化系统相关基因的表达水平。
在不存在AA的情况下，与WT相比，aox1a基因敲除突变体在生理、生化或分子参数上没有表现出任何差异。然而，在AA处理后，aox1a植株的呼吸氧气吸收和依赖NaHCO3的氧气释放均显著降低。叶绿素荧光和P700研究表明，与WT相比，aox1a基因敲除植株无法维持叶绿体电子传递链中的电子流，因此观察到低效的热耗散（低非光化学猝灭）。此外，aox1a突变体在NAD(P)H和抗坏血酸（Asc）的细胞氧化还原对中表现出显著紊乱，因此ROS积累和丙二醛（MDA）含量增加。相比之下，与aox1a突变体相比，WT植株中CSD1、CAT1、sAPX、COX15和AOX1A的转录水平显著增加。
这些结果表明，当通过COX途径的电子传递在复合体III处受到干扰时，AOX1A通过调节细胞氧化还原稳态和ROS生成，在维持叶绿体氧化还原状态和能量供应以优化光合作用方面发挥着重要作用。
