Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow, Russia.
N.M. Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, Moscow, Russia.
Photosynth Res. 2020 Dec;146(1-3):299-329. doi: 10.1007/s11120-020-00777-0. Epub 2020 Aug 11.
The significance of temperature-dependent regulation of photosynthetic apparatus (PSA) is determined by the fact that plant temperature changes with environmental temperature. In this work, we present a brief overview of temperature-dependent regulation of photosynthetic processes in class B chloroplasts (thylakoids) and analyze these processes using a computer model that takes into account the key stages of electron and proton transport coupled to ATP synthesis. The rate constants of partial reactions were parametrized on the basis of experimental temperature dependences of partial photosynthetic processes: (1) photosystem II (PSII) turnover and plastoquinone (PQ) reduction, (2) the plastoquinol (PQH) oxidation by the cytochrome (Cyt) bf complex, (3) the ATP synthase activity, and (4) the proton leak from the thylakoid lumen. We consider that PQH oxidation is the rate-limiting step in the intersystem electron transport. The parametrization of the rate constants of these processes is based on earlier experimental data demonstrating strong correlations between the functional and structural properties of thylakoid membranes that were probed with the lipid-soluble spin labels embedded into the membranes. Within the framework of our model, we could adequately describe a number of experimental temperature dependences of photosynthetic reactions in thylakoids. Computer modeling of electron and proton transport coupled to ATP synthesis supports the notion that PQH oxidation by the Cyt bf complex and proton pumping into the lumen are the basic temperature-dependent processes that determine the overall electron flux from PSII to molecular oxygen and the net ATP synthesis upon variations of temperature. The model describes two branches of the temperature dependence of the post-illumination reduction of [Formula: see text] characterized by different activation energies (about 60 and ≤ 3.5 kJ mol). The model predicts the bell-like temperature dependence of ATP formation, which arises from the balance of several factors: (1) the thermo-induced acceleration of electron transport through the Cyt bf complex, (2) deactivation of PSII photochemistry at sufficiently high temperatures, and (3) acceleration of the passive proton outflow from the thylakoid lumen bypassing the ATP synthase complex. The model describes the temperature dependence of experimentally measured parameter P/2e, determined as the ratio between the rates of ATP synthesis and pseudocyclic electron transport (HO → PSII → PSI → O).
光合作用器官（PSA）的温度依赖性调节的意义在于植物的温度随环境温度的变化而变化。在这项工作中，我们简要概述了 B 类叶绿体（类囊体）中光合作用过程的温度依赖性调节，并使用考虑到电子和质子与 ATP 合成偶联的关键阶段的计算机模型来分析这些过程。部分反应的速率常数是根据部分光合作用过程的实验温度依赖性来参数化的：（1）光系统 II（PSII）周转和质体醌（PQ）还原，（2）质体醌氢（PQH）被细胞色素（Cyt）bf 复合物氧化，（3）ATP 合酶活性，（4）从类囊体腔中漏出质子。我们认为 PQH 氧化是细胞色素（Cyt）bf 复合物中电子传递的限速步骤。这些过程的速率常数的参数化是基于先前的实验数据，这些数据表明类囊体膜的功能和结构特性之间存在很强的相关性，这些相关性是通过将脂溶性自旋标记物嵌入膜中来探测的。在我们的模型框架内，我们可以适当地描述类囊体中光合作用反应的许多实验温度依赖性。电子和质子与 ATP 合成偶联的计算机模拟支持这样的观点，即 Cyt bf 复合物中 PQH 的氧化和质子泵入腔是基本的温度依赖性过程，决定了从 PSII 到分子氧的整体电子通量和温度变化时净 ATP 合成。该模型描述了由不同激活能（约 60 和≤3.5 kJ/mol）特征的 [Formula: see text] 后光照还原的温度依赖性的两个分支。该模型预测了 ATP 形成的钟形温度依赖性，这源于几个因素的平衡：（1）热诱导通过 Cyt bf 复合物加速电子传递，（2）在足够高的温度下 PSII 光化学失活，以及（3）从类囊体腔中被动质子流出绕过 ATP 合酶复合物的加速。该模型描述了实验测量的参数 P/2e 的温度依赖性，该参数定义为 ATP 合成和拟循环电子传递（HO→PSII→PSI→O）的速率之比。
