In-vivo quantification of electron flow through photosystem I - cyclic electron transport makes up about 35 % in a cyanobacterium.
In-vivo quantification of electron flow through photosystem I - cyclic electron transport makes up about 35 % in a cyanobacterium.
复制标题
DOI：
10.1016/j.bbabio.2020.148353
复制
发表时间：
2020-12
期刊：
影响因子：
--
通讯作者：
Marius Theune;S. Hildebrandt;A. Steffen-Heins;W. Bilger;Kirstin Gutekunst;Jens Appel
中科院分区：
文献类型：
--
作者：
Marius Theune;S. Hildebrandt;A. Steffen-Heins;W. Bilger;Kirstin Gutekunst;Jens Appel
光合电子流由光系统I和II驱动，为固碳提供化学能。除了线性模式外，还存在第二种循环路径，它只涉及光系统i。线性和循环输运的确切贡献仍然是一个有争议的问题。在这里，我们首次描述了一种方法的发展，该方法允许通过光合生物的光系统I以绝对术语量化电子流。特定的体内方案允许识别蓝细菌中PSI受体位点的质体青素，P700和fes簇（包括铁氧还蛋白）的氧化还原状态。PCC 6803与近红外光谱仪双klas /近红外。双klas /NIR法测定的P700吸光度变化与EPR法直接测定PSI浓度呈线性相关。暗间隔弛豫动力学测量（DIRKPSI）被用于确定电子通过PSI的流动。计算来自氢氧化的电子作为光系统I的电子供体与dirkpsi测量平行，证实了该方法的有效性。与DIRKPSI相比，经典PSI产率测量的电子流测定高估了低光强度下的电子流，并且更早饱和。与PSII相比，dirkpsi与析氧测量的结合产生了35%的剩余电子通过PSI的比例。我们将这些电子归因于循环电子传递，其强度是植物的两倍。通过计算流经光系统的电子，可以确定光合作用所需的量子数，即每产生一个氧气需要11个量子，这与已发表的数值接近。
Photosynthetic electron flow, driven by photosystem I and II, provides chemical energy for carbon fixation. In addition to a linear mode a second cyclic route exists, which only involves photosystem I. The exact contributions of linear and cyclic transport are still a matter of debate. Here, we describe the development of a method that allows quantification of electron flow in absolute terms through photosystem I in a photosynthetic organism for the first time. Specific in-vivo protocols allowed to discern the redox states of plastocyanin, P700 and the FeS-clusters including ferredoxin at the acceptor site of PSI in the cyanobacteriumSynechocystissp. PCC 6803 with the near-infrared spectrometer Dual-KLAS/NIR. P700 absorbance changes determined with the Dual-KLAS/NIR correlated linearly with direct determinations of PSI concentrations using EPR. Dark-interval relaxation kinetics measurements (DIRKPSI) were applied to determine electron flow through PSI. Counting electrons from hydrogen oxidation as electron donor to photosystem I in parallel to DIRKPSImeasurements confirmed the validity of the method. Electron flow determination by classical PSI yield measurements overestimates electron flow at low light intensities and saturates earlier compared to DIRKPSI. Combination of DIRKPSIwith oxygen evolution measurements yielded a proportion of 35% of surplus electrons passing PSI compared to PSII. We attribute these electrons to cyclic electron transport, which is twice as high as assumed for plants. Counting electrons flowing through the photosystems allowed determination of the number of quanta required for photosynthesis to 11 per oxygen produced, which is close to published values.