XANTHOPHYLL CYCLE-DEPENDENT QUENCHING OF PHOTOSYSTEM-II CHLOROPHYLL-A FLUORESCENCE - FORMATION OF A QUENCHING COMPLEX WITH A SHORT FLUORESCENCE LIFETIME
XANTHOPHYLL CYCLE-DEPENDENT QUENCHING OF PHOTOSYSTEM-II CHLOROPHYLL-A FLUORESCENCE - FORMATION OF A QUENCHING COMPLEX WITH A SHORT FLUORESCENCE LIFETIME
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DOI：
10.1073/pnas.92.6.2273
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发表时间：
1995-03-14
影响因子：
11.1
通讯作者：
GOVINDJEE
中科院分区：
文献类型：
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作者：
GILMORE, AM;HAZLETT, TL;GOVINDJEE
过量的光通过形成类囊体反式pH梯度触发光系统II中激发能的保护性非辐射耗散，从而刺激玉米黄质和花青素的形成。当这些叶黄素与天线色素-蛋白质复合物的质子化结合时，可能增加非辐射耗散，从而抑制叶绿素a荧光。在这里，我们平行测量了叶绿素a的荧光寿命和强度，以了解这一过程的机制。在存在pH梯度（淬灭条件）的情况下，增加叶黄素浓度会降低以约2ns为中心的荧光寿命组分的分数强度，并增加约0.4 ns的荧光寿命组分的分数强度。解耦pH梯度（未淬火条件）消除了0.4 ns组件。在淬灭或未淬灭的样品条件下，叶黄素浓度的变化对荧光寿命没有显著影响。然而，猝灭和未猝灭状态之间的荧光寿命存在差异，这是由于ph相关而非叶黄素相关的过程。最大荧光强度的猝灭与叶黄素浓度和0.4 ns组分的分数强度有关。荧光寿命不变，最大荧光强度和暗电平荧光强度成比例猝灭，表明叶黄素作用于天线而非反应中心过程。此外，荧光猝灭被解释为pH梯度和叶黄素浓度的共同作用，导致荧光寿命短（约0.4 ns）的猝灭配合物的形成。
Excess light triggers protective nonradiative dissipation of excitation energy in photosystem II through the formation of a trans-thylakoid pH gradient that in turn stimulates formation of zeaxanthin and antheraxanthin. These xanthophylls when combined with protonation of antenna pigment-protein complexes may increase nonradiative dissipation and, thus, quench chlorophyll a fluorescence. Here we measured, in parallel, the chlorophyll a fluorescence lifetime and intensity to understand the mechanism of this process. Increasing the xanthophyll concentration in the presence of a pH gradient (quenched conditions) decreases the fractional intensity of a fluorescence lifetime component centered at approximate to 2 ns and increases a component at approximate to 0.4 ns. Uncoupling the pH gradient (unquenched conditions) eliminates the 0.4-ns component. Changes in the xanthophyll concentration do not significantly affect the fluorescence lifetimes in either the quenched or unquenched sample conditions. However, there are differences in fluorescence life-times between the quenched and unquenched states that are due to pH-related, but nonxanthophyll-related, processes. Quenching of the maximal fluorescence intensity correlates with both the xanthophyll concentration and the fractional intensity of the 0.4-ns component. The unchanged fluorescence lifetimes and the proportional quenching of the maximal and dark-level fluorescence intensities indicate that the xanthophylls act on antenna, not reaction center processes. Further, the fluorescence quenching is interpreted as the combined effect of the pH gradient and xanthophyll concentration, resulting in the formation of a quenching complex with a short (approximate to 0.4 ns) fluorescence lifetime.