Contrasting pH-Optima of Light-Driven O2-and H2O2-Reduction in Spinach Chloroplasts as Measured via Chlorophyll Fluorescence Quenching
Contrasting pH-Optima of Light-Driven O2-and H2O2-Reduction in Spinach Chloroplasts as Measured via Chlorophyll Fluorescence Quenching
复制标题
通过叶绿素荧光猝灭测量菠菜叶绿体光驱动 O2 和 H2O2 还原的 pH 最佳值对比
DOI：
10.1515/znc-1991-7-821
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
C. Neubauer
中科院分区：
文献类型：
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作者：
U. Schreiber;H. Reising;C. Neubauer
摘要采用饱和脉冲法进行叶绿素荧光猝灭分析，研究了具有高抗坏血酸过氧化物酶活性的完整菠菜叶绿体中依赖于O2的电子流的pH依赖性。当羧化酶/加氧酶活性被阻断时，光化学猝灭和非光化学猝灭最初是低的，并且随着光照时间的延长而增加。猝灭的最适pH值在pH 6.5左右，但只有当Δ的pH-形成被允许时才能出现。我们认为，整个依赖O2的电子流包括两个主要组成部分，即O2-还原(Mehler反应)和Mehler反应中生成的H2O2的还原，涉及抗坏血酸过氧化物酶和单脱氢抗坏血酸还原酶的活性。光驱动O2-还原(KCN存在)和H_2O_2-还原(厌氧条件)的pH依赖关系分别在pH为5和8.5附近显示出相反的最适pH。依赖于能量的、暗可弛豫的非光化学猝灭不是用O2-还原而是用双氧水还原观察到的，而且只有在pH-6.5时才能观察到。讨论了这些发现与光合作用电子流调节的相关性。结果表明，在同化电子流受限的情况下，非依赖于O2的同化流负责Δ的pH-形成，并通过这种非同化流的自身催化作用而被激发。这一自催化反应序列是叶绿素荧光诱导的“考茨基效应”的基础。
Abstract Quenching analysis of chlorophyll fluorescence by the saturation pulse method is used to investigate the pH-dependency of O2-dependent electron flow in intact spinach chloroplasts with high ascorbate peroxidase activity. When carboxylase/oxygenase activity is blocked, photochemical and non-photochemical quenching are initially low and increase with illumination time. Quenching shows a pH-optimum around pH 6.5, but only when ΔpH-formation is al lowed. It is suggested that overall O2-dependent electron flow involves two major components, namely O2-reduction (Mehlerreaction) and reduction of the H2O2 formed in the Mehlerreaction, involving enzymic activity of ascorbate peroxidase and monodehydroascorbate reductase. The separated pH-dependencies of light driven O2-reduction (presence of KCN) and of H2O2-reduction (anaerobic conditions) reveal contrasting pH-optima around pH 5 and 8.5, respectively. Energy-dependent, dark relaxable non-photochemical quenching is not observed with O2-reduction but with H2O2-reduction, and only at pH-values above 6.5. The relevance of these findings with respect to regulation of photosynthetic electron flow is discussed. It is suggested that upon limitation of assimilatory electron flow O2-dependent non-assimilatory flow is responsible for ΔpH-formation, by which it is autocatalytically stimulated. It is proposed that this autocatalytical reaction sequence is the basis of the so-called “Kautsky effect” of chlorophyll fluorescence induction.