Boussardon Clément, Hussain Shah, Keech Olivier
Department of Plant Physiology, Umeå Plant Science, Umeå University, Umeå, Sweden.
Physiol Plant. 2025 Sep-Oct;177(5):e70465. doi: 10.1111/ppl.70465.
A leaf is an organ composed of different tissues that fulfill specific functions. We hypothesized that since cells in vascular or mesophyll tissues as well as in stoma are developmentally tuned to operate their functions, mitochondria from these cells could exhibit significant metabolic differences. Using the IMTACT method, mitochondria were isolated from these three specific cell types, and the subsequent proteomes were analyzed. At steady state, mitochondria from vascular and guard cells had a significantly higher abundance of proteins associated with the mtETC, the TCA cycle, and the metabolic use of amino acids (glutamate, proline, isoleucine, leucine, and valine) as alternative substrates. Intriguingly, the mitochondria from guard cells also had a much lower abundance of proteins involved in the translation machinery, thus raising questions about the efficiency of the mitochondrial protein turnover in these cells. In a second step, we carried out the same comparative analysis, but with plants that were subjected to carbon starvation by placing them in prolonged darkness for three or 6 days. For all cell types studied, an increased abundance of proteins involved in branched-chain amino acid metabolism was detected. However, while guard cell mitochondria underwent a drastic reduction in proteins involved in respiration, translation, and RNA editing, suggesting a sharp downregulation of mitochondrial functions, mitochondrial proteomes from mesophyll and vascular cells did not show many differences, except for an increased arginine/proline/glutamate metabolism. Together, the results reported here support a differential regulation of the mitochondrial metabolism among the cell types constituting a leaf, a difference that is exacerbated upon stress.
叶片是由履行特定功能的不同组织组成的器官。我们推测，由于维管组织或叶肉组织以及气孔中的细胞在发育过程中被调整以发挥其功能，这些细胞中的线粒体可能表现出显著的代谢差异。使用IMTACT方法，从这三种特定细胞类型中分离出线粒体，并对随后的蛋白质组进行分析。在稳态下，维管细胞和保卫细胞中的线粒体与线粒体电子传递链（mtETC）、三羧酸循环（TCA循环）以及作为替代底物的氨基酸（谷氨酸、脯氨酸、异亮氨酸、亮氨酸和缬氨酸）的代谢利用相关的蛋白质丰度显著更高。有趣的是，保卫细胞中的线粒体参与翻译机制的蛋白质丰度也低得多，因此引发了关于这些细胞中线粒体蛋白质周转效率的问题。在第二步中，我们进行了相同的比较分析，但使用的是通过将其置于长时间黑暗中3天或6天而遭受碳饥饿的植物。对于所有研究的细胞类型，检测到参与支链氨基酸代谢的蛋白质丰度增加。然而，虽然保卫细胞线粒体中参与呼吸、翻译和RNA编辑的蛋白质大幅减少，表明线粒体功能急剧下调，但叶肉细胞和维管细胞的线粒体蛋白质组除了精氨酸/脯氨酸/谷氨酸代谢增加外，没有显示出许多差异。总之，此处报道的结果支持构成叶片的不同细胞类型中线粒体代谢的差异调节，这种差异在应激时会加剧。
