Sharma Shruti, Sehrawat Ankita, Deswal Renu
Molecular Plant Physiology and Proteomics Laboratory, Department of Botany, University of Delhi, India.
Molecular Plant Physiology and Proteomics Laboratory, Department of Botany, University of Delhi, India.
Plant Sci. 2016 Sep;250:20-29. doi: 10.1016/j.plantsci.2016.05.013. Epub 2016 May 26.
Reactive Oxygen Species (ROS) are important regulatory molecules governing physiological processes. In the present study a biochemical and proteome level comparison of two contrasting growth stages of Dioscorea alata tuber namely germinating and mature tuber was performed in order to understand the tuber physiology and biochemistry. Existence of all the component enzymes [APx (ascorbate peroxidase), GR (glutathione reductase), DHAR (dehydroascorbate reductase), MDHAR (mono-dehydroascorbate reductase)] and major products [ascorbate (ASC) and glutathione (GSH)] of the cycle showed an operational Asada-Halliwell cycle in the tuber. A 2.65 fold increase in ASC content & a 3.8 fold increase in GR activity fortified the redox milieu during germination. In contrast a 5 fold higher H2O2 content (due to 3.08 fold lower APx activity) and accumulation of reactive nitrogen species (RNS) such as nitric oxide (NO, 2.4-fold) and S-nitrosothiol (SNO, 2.08 fold) contributed to overall oxidative conditions in the mature tuber. The carbonic anhydrase (CA, 7.5 fold), DHAR (5.31 fold) and MDHAR (7 fold) activities were higher in the germinating tuber in comparison with the mature tuber. GSNO negatively regulated the CA (3.6 & 3.95 fold), MDHAR (7.5 & 1.5 fold) and APx (2.3 & 1.81 fold) while another NO donor, CysNO negatively regulated the DHAR (2.24 & 1.32 fold) activity in the mature and germinating stages respectively indicating again that the lesser inhibition by NO (via nitrosylation) may be because of overall reducing environment in the germinating tuber. Increased SNO leading to S-nitrosylation of dioscorin was confirmed by Biotin switch assay. This is the first report showing dioscorin nitrosylation. The present analysis showed differential redox regulation and also suggests the physiological relevance of CA, DHAR, MDHAR, APx & GR in tuber germination for the first time. These enzymes may be used as potential markers of tuber germination in future.
活性氧（ROS）是调控生理过程的重要分子。在本研究中，为了解薯蓣块茎的生理生化特性，对薯蓣块茎的两个不同生长阶段即发芽块茎和成熟块茎进行了生化和蛋白质组水平的比较。循环中所有组成酶[抗坏血酸过氧化物酶（APx）、谷胱甘肽还原酶（GR）、脱氢抗坏血酸还原酶（DHAR）、单脱氢抗坏血酸还原酶（MDHAR）]和主要产物[抗坏血酸（ASC）和谷胱甘肽（GSH）]的存在表明块茎中存在有效的阿萨达 - 哈利威尔循环。发芽过程中ASC含量增加2.65倍，GR活性增加3.8倍，强化了氧化还原环境。相比之下，成熟块茎中H2O2含量高5倍（由于APx活性降低3.08倍）以及活性氮物质（RNS）如一氧化氮（NO，增加2.4倍）和亚硝基硫醇（SNO，增加2.08倍）的积累导致了整体氧化状态。与成熟块茎相比，发芽块茎中的碳酸酐酶（CA，增加7.5倍）、DHAR（增加5.31倍）和MDHAR（增加7倍）活性更高。GSNO分别在成熟和发芽阶段对CA（3.6和3.95倍）、MDHAR（7.5和1.5倍）和APx（2.3和1.81倍）产生负调控，而另一种NO供体CysNO分别在成熟和发芽阶段对DHAR（2.24和1.32倍）活性产生负调控，再次表明发芽块茎中由于整体还原环境，NO（通过亚硝基化）的抑制作用较小。生物素转换试验证实了SNO增加导致薯蓣球蛋白的亚硝基化。这是首次报道薯蓣球蛋白的亚硝基化。本分析显示了不同的氧化还原调控，并且首次表明了CA、DHAR、MDHAR、APx和GR在块茎发芽中的生理相关性。这些酶未来可能用作块茎发芽的潜在标志物。
