Department of Molecular Plant Physiology, Institute of Environmental Biology, Faculty of Biology, University of Warsaw, Miecznikowa 1, 02-096 Warsaw, Poland.
J Photochem Photobiol B. 2023 Oct;247:112780. doi: 10.1016/j.jphotobiol.2023.112780. Epub 2023 Aug 25.
This study aimed to examine enzymatic kinetics of photosystem II (PSII) of maize mesophyll chloroplasts using the artificial electron acceptor 2,6-dichloro-1,4-benzoquinone (DCBQ) as a substrate. We extended Michealis-Menten kinetics model assuming that DCBQ can accept electrons from PSII in two ways: from a Q directly or from Q by docking in the Q site. We used a Clark oxygen electrode for measuring the PSII activity, depending on the concentration of DCBQ. We found that: [1] DCBQ acts as an electron acceptor or [2] as an inhibitor for PSII. At a concentration < 0.2 mM, DCBQ accepted electrons from the Q at a rate of 889 electrons/s, while at >> 0.2 mM it replaced Q following which the activity decreased to zero. DCBQ located in the Q also increased the affinity of the substrate to PSII. We determined the kinetic parameters for the chloroplasts of plants growing under high and low light intensity, to change thylakoid stacking and thus the rate of electron transport. The parameter K, which is a measure of the affinity of DCBQ to PSII, showed quantitative changes based on light intensity, while K was proportional to the size of the plastoquinone pool. We believe that our model can be applied as a tool to study "State transitions" and induced changes in grana stacking in plants exposed to various stresses, which will facilitate the regulation of electron transfer pathways through an appropriate balance between linear and cyclic electron transport.
本研究旨在使用人工电子受体 2,6-二氯-1,4-苯醌 (DCBQ) 作为底物，研究玉米质体叶绿体光系统 II (PSII) 的酶动力学。我们扩展了米氏-门捷列夫动力学模型，假设 DCBQ 可以通过两种方式从 PSII 接受电子：直接从 Q 接受或通过在 Q 位停靠从 Q 接受。我们使用克拉克氧电极测量 PSII 活性，该活性取决于 DCBQ 的浓度。我们发现：[1] DCBQ 作为电子受体或 [2] 作为 PSII 的抑制剂。在浓度 <0.2 mM 时，DCBQ 以 889 个电子/s 的速率从 Q 接受电子，而在 >>0.2 mM 时，它取代 Q 后，活性降至零。位于 Q 中的 DCBQ 还增加了底物与 PSII 的亲和力。我们确定了在高光强和低光强下生长的植物的叶绿体的动力学参数，以改变类囊体堆叠，从而改变电子传递速率。参数 K 是衡量 DCBQ 与 PSII 亲和力的指标，它显示出基于光强度的定量变化，而 K 与质体醌池的大小成正比。我们相信，我们的模型可以作为一种工具来研究“状态转换”和暴露于各种胁迫下的植物中粒状堆叠的诱导变化，这将通过在线性和循环电子传递之间取得适当平衡来促进电子传递途径的调节。
