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Identification of a mechanism of photoprotective energy dissipation in higher plants

机译：确定高等植物光保护能量耗散的机制

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Under conditions of excess sunlight the efficient light-harvesting antenna found in the chloroplast membranes of plants is rapidly and reversibly switched into a photoprotected quenched state in which potentially harmful absorbed energy is dissipated as heat, a process measured as the non-photochemical quenching of chlorophyll fluorescence or qE. Although the biological significance of qE is established, the molecular mechanisms involved are not. LHCII, the main light-harvesting complex, has an inbuilt capability to undergo transformation into a dissipative state by conformational change and it was suggested that this provides a molecular basis for qE, but it is not known if such events occur in vivo or how energy is dissipated in this state. The transition into the dissipative state is associated with a twist in the configuration of the LHCII-bound carotenoid neoxanthin, identified using resonance Raman spectroscopy. Applying this technique to study isolated chloroplasts and whole leaves, we show here that the same change in neoxanthin configuration occurs in vivo, to an extent consistent with the magnitude of energy dissipation. Femtosecond transient absorption spectroscopy, performed on purified LHCII in the dissipative state, shows that energy is transferred from chlorophyll a to a low-lying carotenoid excited state, identified as one of the two luteins (lutein1) in LHCII. Hence, it is experimentally demonstrated that a change in conformation of LHCII occurs in vivo, which opens a channel for energy dissipation by transfer to a bound carotenoid. We suggest that this is the principal mechanism of photoprotection.
机译：在阳光过多的条件下，植物叶绿体膜中发现的有效的光收集天线迅速可逆地转换为光保护猝灭状态，在该状态下，潜在有害吸收的吸收能以热量的形式散失，该过程被称为叶绿素的非光化学猝灭荧光或qE。尽管qE的生物学意义已经确立，但所涉及的分子机制尚未阐明。 LHCII是主要的光收集复合体，具有通过构象变化转化为耗散状态的内在能力，并且有人提出这为qE提供了分子基础，但尚不清楚此类事件是否在体内发生或如何发生。在这种状态下消散。过渡到耗散状态与LHCII结合的类胡萝卜素新黄嘌呤构型的扭曲有关，这是通过共振拉曼光谱法确定的。应用这项技术研究离体的叶绿体和整片叶子，我们在这里表明，在体内黄嘌呤新构型发生了相同的变化，其程度与能量耗散的大小一致。飞秒瞬态吸收光谱法对耗散状态的纯化LHCII进行了分析，结果表明能量从叶绿素a转移到低水平的类胡萝卜素激发态，该状态被认为是LHCII中的两种叶黄素（lutein1）之一。因此，实验证明了体内LHCII构象的变化，这为转移至结合的类胡萝卜素打开了能量消散的通道。我们建议这是光保护的主要机制。

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