A.N.Belozersky Institute of Physical-Chemical Biology, M.V.Lomonosov Moscow State University, Moscow, Russia.
N.M.Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, Moscow, Russia.
Photosynth Res. 2019 Mar;139(1-3):509-522. doi: 10.1007/s11120-018-0494-z. Epub 2018 Mar 7.
In plants, the short-term regulation (STR, seconds to minute time scale) of photosynthetic apparatus is associated with the energy-dependent control in the chloroplast electron transport, the distribution of light energy between photosystems (PS) II and I, activation/deactivation of the Calvin-Benson cycle (CBC) enzymes, and relocation of chloroplasts within the plant cell. In this work, using a dual-PAM technique for measuring the time-courses of P photooxidation and Chl a fluorescence, we have investigated the STR events in Tradescantia fluminensis leaves. The comparison of Chl a fluorescence and [Formula: see text] induction allowed us to investigate the contribution of the trans-thylakoid pH difference (ΔpH) to the STR events. Two parameters were used as the indicators of ΔpH generation: pH-dependent component of non-photochemical quenching of Chl a fluorescence, and pH-dependent rate of electron transfer from plastoquinol (PQH) to [Formula: see text] (via the Cyt bf complex and plastocyanin). In dark-adapted leaves, kinetics of [Formula: see text] induction revealed three phases. Initial phase is characterized by rapid electron flow to [Formula: see text] (τ ~ 5-10 ms), which is likely related to cyclic electron flow around PSI, while the outflow of electrons from PSI is restricted by slow consumption of NADPH in the CBC. The light-induced generation of ΔpH and activation of the CBC promote photooxidation of P and concomitant retardation of [Formula: see text] reduction (τ ~ 20 ms). Prolonged illumination induces additional slowing down of electron transfer to [Formula: see text] (τ ≥ 30-35 ms). The latter effect is not accompanied by changes in the Chl a fluorescence parameters which are sensitive to ΔpH generation. We suggest the tentative explanation of the latter results by the reversal of Q-cycle, which causes the deceleration of PQH oxidation due to the back pressure of stromal reductants.
在植物中，光合作用装置的短期调节（STR，秒到分钟时间尺度）与叶绿体电子传递中的能量依赖控制、光合系统（PS）II 和 I 之间的光能分布、卡尔文-本森循环（CBC）酶的激活/失活以及叶绿体在植物细胞内的重定位有关。在这项工作中，我们使用双 PAM 技术测量 P 光氧化和 Chl a 荧光的时间过程，研究了 Tradescantia fluminensis 叶片中的 STR 事件。Chl a 荧光和 [Formula: see text] 诱导的比较允许我们研究跨类囊体 pH 差（ΔpH）对 STR 事件的贡献。我们使用两个参数作为 ΔpH 产生的指标：Chl a 荧光的非光化学猝灭的 pH 依赖性成分，以及来自 plastoquinol (PQH) 的电子向 [Formula: see text] 的 pH 依赖性转移速率（通过 Cyt bf 复合物和质体蓝素）。在暗适应的叶子中，[Formula: see text] 诱导的动力学显示出三个阶段。初始阶段的特点是电子快速流向 [Formula: see text]（τ ~ 5-10 ms），这可能与 PSI 周围的循环电子流有关，而 PSI 中的电子流出受到 CBC 中 NADPH 缓慢消耗的限制。ΔpH 的光诱导产生和 CBC 的激活促进 P 的光氧化，同时减缓 [Formula: see text] 的还原（τ ~ 20 ms）。长时间的光照会诱导电子向 [Formula: see text] 的转移进一步减慢（τ≥ 30-35 ms）。后一种效应不会伴随着对 ΔpH 产生敏感的 Chl a 荧光参数的变化。我们通过 Q 循环的反转对后一种结果提出了试探性的解释，这导致 PQH 氧化的减速是由于基质还原剂的反压。
