Institute of Botany, University of Münster, Schlossgarten 3, D-48149, Münster, Germany.
Photosynth Res. 1993 Aug;37(2):117-30. doi: 10.1007/BF02187470.
pH-dependent inactivation of Photosystem (PS) II and related quenching of chlorophyll-a-fluorescence have been investigated in isolated thylakoids and PS II-particles and related to calcium release at the donor side of PS II. The capacity of oxygen evolution (measured under light saturation) decreases when the ΔpH is high and the pH in the thylakoid lumen decreases below 5.5. Oxygen evolution recovers upon uncoupling. The pH-response of inactivation can be described by a 1 H(+)-transition with an apparent pK-value of about 4.7. The yield of variable fluorescence decreases in parallel to the inactivation of oxygen evolution. pH-dependent quenching requires light and can be inhibited by DCMU. In PS II-particles, inactivation is accompanied by a reversible release of Ca(2+)-ions (one Ca(2+) released per 200 Chl). In isolated thylakoids, where a ΔpH was created by ATP-hydrolysis, both inactivation of oxygen evolution (and related fluorescence quenching) by internal acidification and the recovery of that inactivation can be suppressed by calcium-channel blockers. In the presence of the Ca(2+)-ionophore A23187, recovery of Chl-fluorescence (after relaxation of the ΔpH) is stimulated by external Ca(2+) and retarded by EGTA. As shown previously (Krieger and Weis 1993), inactivation of oxygen evolution at low pH is accompanied by an upward shift of the midpoint redox-potential, Em, of QA. Here, we show that in isolated PS II particles the pH-dependent redox-shift (about 160 mV, as measured from redox titration of Chl-fluorescence) is suppressed by Ca(2+)-channel blockers and DCMU. When a redox potential of -80 to -120mV was established in a suspension of isolated thylakoids, the primary quinone acceptor, QA, was largely reduced in presence of a ΔpH (created by ATP-hydrolysis) but oxidized in presence of an uncoupler. Ca(2+)-binding at the lumen side seems to control redox processes at the lumen- and stroma-side of PS II. We discuss Ca(2+)-release to be involved in the physiological process of 'high energy quenching'.
pH 依赖性的 PSII 失活和与之相关的叶绿素-a 荧光淬灭已在分离的类囊体和 PSII 颗粒中进行了研究，并与 PSII 供体侧的钙释放有关。当 ΔpH 较高且类囊体腔中的 pH 下降到 5.5 以下时，氧气的产生能力（在光饱和下测量）会降低。解偶联后氧气的产生能力会恢复。失活的 pH 响应可以用一个表观 pK 值约为 4.7 的 1 H(+)转换来描述。可变荧光的产量与氧气产生的失活呈平行下降。pH 依赖性的淬灭需要光，并可被 DCMU 抑制。在 PSII 颗粒中，失活伴随着可被 Ca(2+)通道阻滞剂抑制的可逆 Ca(2+)离子释放（每 200 个叶绿素释放一个 Ca(2+)）。在通过 ATP 水解产生 ΔpH 的分离的类囊体中，内部酸化导致的氧气产生的失活（以及相关的荧光淬灭）和失活的恢复都可以被 Ca(2+)通道阻滞剂抑制。在 Ca(2+)离子载体 A23187 的存在下，外源性 Ca(2+)可刺激 Chl 荧光（在 ΔpH 弛豫后）的恢复，而 EGTA 则会延迟其恢复。如前所述（Krieger 和 Weis，1993），在低 pH 下氧气的产生失活伴随着 QA 的中点氧化还原电位 Em 的向上移动。在这里，我们表明在分离的 PSII 颗粒中，pH 依赖性的氧化还原移位（约 160 mV，如通过 Chl 荧光的氧化还原滴定测量）被 Ca(2+)通道阻滞剂和 DCMU 抑制。当在分离的类囊体悬浮液中建立-80 至-120 mV 的氧化还原电势时，在 ΔpH（由 ATP 水解产生）存在下，主要的醌受体 QA 大部分被还原，但在解偶联剂存在下被氧化。腔侧的 Ca(2+)结合似乎控制着 PSII 腔侧和基质侧的氧化还原过程。我们讨论了 Ca(2+)释放可能参与了“高能量猝灭”的生理过程。
