Mahati Kandarpa, Padmasree Kollipara
Department of Biotechnology and Bioinformatics, School of Life Sciences, University of Hyderabad, Gachibowli, Hyderabad, India.
Front Plant Sci. 2023 Apr 11;14:1099474. doi: 10.3389/fpls.2023.1099474. eCollection 2023.
The current experimental data unveils the role of brassinolide (BL), a phytohormone of class brassinosteroids (BRs), in augmenting the cross-talk between the mitochondrial electron transport chain (mETC) and chloroplasts to strengthen the efficiency of the Calvin-Benson cycle (CBC) for higher assimilation of carbon dioxide in the mesophyll cell protoplasts (MCP) of . The outcome of total respiration (TR) and photosynthetic carbon assimilation (PCA) was monitored as O uptake under dark and NaHCO-dependent O evolution under light, respectively, after pre-incubation of MCP at a broad spectrum of BL concentration from 0.05 pM to 5 pM at 25 °C and optimum light intensity of 1000 μmol m s. The addition of optimal concentration (0.5 pM) of BL to MCP stimulated the (i) TR, (ii) PCA, and (iii) -benzoquinone-dependent O evolution (PSII activity). Further, in response to BL, the enzyme activity or transcript levels of redox-regulated CBC enzymes and glucose-6-phosphate raised considerably. Also, the addition of BL to MCP remarkably accelerated the capacity of the cytochrome oxidase (COX) and alternative oxidase (AOX) pathways concurrently with an increase in total cellular pyruvate and reactive oxygen species (ROS) levels. Besides, malate valve components (Malate, , ) increased in response to BL. At the same time, the cellular redox ratios of pyridine nucleotides (NADPH and NADH) were kept low in the presence of BL. However, BL could not keep up the CBC activity of photosynthesis along with its associated light-activated enzymes/transcripts when mETC through COX or AOX pathway is restricted by antimycin A (AA) or salicylhydroxamic acid (SHAM), respectively. In contrast, adding BL to MCP under restricted mETC showed aggravation in total cellular ROS, pyruvate, malate, and redox ratio of pyridine nucleotides with a concomitant increase in transcripts associated with malate valve and antioxidant systems. These results suggest that BL enhances the PCA by coordinating in cross-talk of chloroplasts and mitochondria to regulate the cellular redox ratio or ROS through the involvement of COX and AOX pathways along with the malate valve and antioxidant systems.
目前的实验数据揭示了油菜素内酯（BL）——一种油菜素甾醇类（BRs）植物激素——在增强线粒体电子传递链（mETC）与叶绿体之间的相互作用，以提高卡尔文-本森循环（CBC）效率，从而在叶肉细胞原生质体（MCP）中更高效率地同化二氧化碳方面的作用。在25℃和1000 μmol m⁻² s⁻¹的最佳光照强度下，将MCP在0.05 pM至5 pM的宽浓度范围内的BL中预孵育后，分别监测总呼吸（TR）和光合碳同化（PCA）的结果，即黑暗条件下的氧气吸收和光照条件下依赖NaHCO₃的氧气释放。向MCP中添加最佳浓度（0.5 pM）的BL刺激了：（i）TR，（ii）PCA，以及（iii）对苯醌依赖性氧气释放（PSII活性）。此外，响应于BL，氧化还原调节的CBC酶和6-磷酸葡萄糖的酶活性或转录水平显著提高。而且，向MCP中添加BL显著加速了细胞色素氧化酶（COX）和交替氧化酶（AOX）途径的能力，同时细胞总丙酮酸和活性氧（ROS）水平增加。此外，苹果酸阀组分（苹果酸、 、 ）响应于BL而增加。同时，在存在BL的情况下，吡啶核苷酸（NADPH和NADH）的细胞氧化还原比率保持较低。然而，当mETC分别通过COX途径或AOX途径受到抗霉素A（AA）或水杨羟肟酸（SHAM）限制时，BL无法维持光合作用的CBC活性及其相关的光激活酶/转录本。相反，在受限的mETC条件下向MCP中添加BL会导致细胞总ROS、丙酮酸、苹果酸以及吡啶核苷酸氧化还原比率增加，同时与苹果酸阀和抗氧化系统相关的转录本也会增加。这些结果表明，BL通过协调叶绿体和线粒体的相互作用，通过COX和AOX途径以及苹果酸阀和抗氧化系统的参与来调节细胞氧化还原比率或ROS，从而增强PCA。
