Gilad Gal, Sapir Omer, Hipsch Matanel, Waiger Daniel, Ben-Ari Julius, Zeev Bar Ben, Zait Yotam, Lampl Nardy, Rosenwasser Shilo
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Center for Scientific Imaging Core Facility, The Robert H. Smith Faculty of Agriculture, Food & Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Plant Cell Environ. 2025 May;48(5):3559-3572. doi: 10.1111/pce.15368. Epub 2025 Jan 9.
Nitrate reduction requires reducing equivalents produced by the photosynthetic electron transport chain. Therefore, it has been suggested that nitrate assimilation provides a sink for electrons under high light conditions. We tested this hypothesis by monitoring photosynthetic efficiency and the chloroplastic glutathione redox potential (chl-E) of plant lines with mutated glutamine synthetase 2 (GS2) and ferredoxin-dependent glutamate synthase 1 (GOGAT1). Mutant lines incorporated significantly less isotopically-labelled nitrate into amino acids than wild-type plants, demonstrating impaired nitrogen assimilation. When nitrate assimilation was compromised, photosystem II (PSII) proved more vulnerable to photodamage. The effect of the nitrate assimilation pathway on the chl- E was monitored using the chloroplast-targeted roGFP2 biosensor (chl-roGFP2). Remarkably, while oxidation followed by reduction of chl-roGFP2 was detected in WT plants in response to high light, oxidation values were stable in the mutant lines, suggesting that chl-E relaxation after high light-induced oxidation is achieved by diverting excess electrons to the nitrogen assimilation pathway. Importantly, similar ΦPSII and chl-roGFP2 patterns were observed at elevated CO suggesting that mutant phenotypes are not associated with photorespiration activity. Together, these findings indicate that the nitrogen assimilation pathway serves as a sustainable energy dissipation route, ensuring efficient photosynthetic activity and fine-tuning redox metabolism under light-saturated conditions.
硝酸盐还原需要光合电子传递链产生的还原当量。因此，有人提出在高光条件下，硝酸盐同化作用为电子提供了一个汇。我们通过监测谷氨酰胺合成酶2（GS2）和铁氧还蛋白依赖性谷氨酸合酶1（GOGAT1）突变的植株系的光合效率和叶绿体谷胱甘肽氧化还原电位（chl-E）来验证这一假设。与野生型植株相比，突变株系将同位素标记的硝酸盐掺入氨基酸的量显著减少，这表明氮同化作用受损。当硝酸盐同化作用受到损害时，光系统II（PSII）被证明更容易受到光损伤。使用叶绿体靶向的roGFP2生物传感器（chl-roGFP2）监测硝酸盐同化途径对chl-E的影响。值得注意的是，虽然在野生型植株中检测到高光照射后chl-roGFP2先氧化后还原，但在突变株系中氧化值保持稳定，这表明高光诱导氧化后chl-E的恢复是通过将多余的电子转移到氮同化途径来实现的。重要的是，在高浓度二氧化碳条件下观察到了类似的PSII有效量子产率（ΦPSII）和chl-roGFP2模式，这表明突变表型与光呼吸活性无关。总之，这些发现表明氮同化途径是一条可持续的能量耗散途径，可确保在光饱和条件下高效的光合活性并微调氧化还原代谢。
