Group of Antioxidants, Free Radicals and Nitric Oxide in Biotechnology, Food and Agriculture, Spain.
Group of Ion Homeostasis, Department of Biochemistry, Cell and Molecular Biology of Plants, Estación Experimental Del Zaidín, CSIC, C/ Profesor Albareda, 1, 18008, Granada, Spain.
Plant Physiol Biochem. 2021 Mar;160:106-119. doi: 10.1016/j.plaphy.2021.01.010. Epub 2021 Jan 12.
Potassium (K) exerts key physiological functions such as osmoregulation, stomatal movement, membrane transport, protein synthesis and photosynthesis among others. Previously, it was demonstrated in Arabidopsis thaliana that the loss of function of the chloroplast KEfflux Antiporters KEA1 and KEA2, located in the inner envelope membrane, provokes inefficient photosynthesis. Therefore, the main goal of this study was to evaluate the potential impact of the loss of function of those cation transport systems in the metabolism of reactive oxygen and nitrogen species (ROS and RNS). Using 14-day-old seedlings from Arabidopsis double knock-out kea1kea2 mutants, ROS metabolism and NO content in roots and green cotyledons were studied at the biochemical level. The loss of function of AtKEA1 and AtKEA2 did not cause oxidative stress but it provoked an alteration of the ROS homeostasis affecting some ROS-generating enzymes. These included glycolate oxidase (GOX) and NADPH-dependent superoxide generation activity, enzymatic and non-enzymatic antioxidants and both NADP-isocitrate dehydrogenase and NADP-malic enzyme activities. NO content, analyzed by confocal laser scanning microscopy (CLSM), was negatively affected in both photosynthetic and non-photosynthetic organs in kea1kea2 mutant seedlings. Furthermore, the S-nitrosoglutathione reductase (GSNOR) protein expression and activity were downregulated in kea1kea2 mutants, whereas the tyrosine nitrated protein profile, analyzed by immunoblot, was unaffected but the relative expression of each immunoreactive band changed. Moreover, kea1kea2 mutants showed an increased photorespiratory pathway and stomata closure, thus promoting a higher resilience to drought stress. Data suggest that the chloroplast osmotic balance and integrity maintained by AtKEA1 and AtKEA2 are necessary to keep the balance of ROS/RNS metabolism. Moreover, these data open new questions about how endogenous NO generation might be affected by the K/H transport located in the chloroplasts.
钾（K）发挥着重要的生理功能，如渗透调节、气孔运动、膜转运、蛋白质合成和光合作用等。此前，在拟南芥中已经证明，位于内囊膜的叶绿体 K 外排转运体 KEA1 和 KEA2 的功能丧失会导致光合作用效率低下。因此，本研究的主要目标是评估这些阳离子转运系统的功能丧失对活性氧和氮物种（ROS 和 RNS）代谢的潜在影响。使用拟南芥双敲除 kea1kea2 突变体的 14 天大的幼苗，在生化水平上研究了根和绿色子叶中 ROS 代谢和 NO 含量。AtKEA1 和 AtKEA2 的功能丧失不会引起氧化应激，但会引起 ROS 动态平衡的改变，影响一些 ROS 生成酶。这些酶包括甘氨酸氧化酶（GOX）和 NADPH 依赖性超氧化物生成活性、酶和非酶抗氧化剂以及 NADP-异柠檬酸脱氢酶和 NADP-苹果酸酶活性。通过共聚焦激光扫描显微镜（CLSM）分析，NO 含量在 kea1kea2 突变体幼苗的光合作用和非光合作用器官中均受到负面影响。此外，kea1kea2 突变体中的 S-亚硝基谷胱甘肽还原酶（GSNOR）蛋白表达和活性下调，而通过免疫印迹分析的酪氨酸硝化蛋白谱不受影响，但每个免疫反应带的相对表达发生了变化。此外，kea1kea2 突变体表现出增强的光呼吸途径和气孔关闭，从而提高了对干旱胁迫的抵抗力。数据表明，由 AtKEA1 和 AtKEA2 维持的叶绿体渗透平衡和完整性对于保持 ROS/RNS 代谢平衡是必要的。此外，这些数据提出了关于内源性 NO 生成如何受到位于叶绿体中的 K/H 转运影响的新问题。
