Department of Theoretical Physics, Faculty of Physics, Vilnius University, Saulėtekio Avenue 9, LT-10222 Vilnius, Lithuania.
Department of Molecular Compound Physics, Centre for Physical Sciences and Technology, Saulėtekio Avenue 3, LT-10222 Vilnius, Lithuania.
Nat Plants. 2016 Apr 18;2(5):16045. doi: 10.1038/nplants.2016.45.
The photosynthetic apparatus of green plants is well known for its extremely high efficiency that allows them to operate under dim light conditions. On the other hand, intense sunlight may result in overexcitation of the light-harvesting antenna and the formation of reactive compounds capable of 'burning out' the whole photosynthetic unit. Non-photochemical quenching is a self-regulatory mechanism utilized by green plants on a molecular level that allows them to safely dissipate the detrimental excess excitation energy as heat. Although it is believed to take place in the plant's major light-harvesting complexes (LHC) II, there is still no consensus regarding its molecular nature. To get more insight into its physical origin, we performed high-resolution time-resolved fluorescence measurements of LHCII trimers and their aggregates across a wide temperature range. Based on simulations of the excitation energy transfer in the LHCII aggregate, we associate the red-emitting state, having fluorescence maximum at ∼700 nm, with the partial mixing of excitonic and chlorophyll-chlorophyll charge transfer states. On the other hand, the quenched state has a totally different nature and is related to the incoherent excitation transfer to the short-lived carotenoid excited states. Our results also show that the required level of photoprotection in vivo can be achieved by a very subtle change in the number of LHCIIs switched to the quenched state.
绿色植物的光合作用装置以其极高的效率而闻名，这使它们能够在弱光条件下进行光合作用。另一方面，强烈的阳光可能会导致光捕获天线的过激发，并形成能够“烧毁”整个光合作用单元的反应性化合物。非光化学猝灭是绿色植物在分子水平上利用的一种自我调节机制，使它们能够安全地将有害的多余激发能以热量的形式耗散。尽管人们认为它发生在植物的主要光捕获复合物（LHC）II 中，但对于其分子性质仍没有共识。为了更深入地了解其物理起源，我们在很宽的温度范围内对 LHCII 三聚体及其聚集体进行了高分辨率时间分辨荧光测量。基于 LHCII 聚集体中激发能转移的模拟，我们将发射波长在约 700nm 的红色发射态与激子和叶绿素-叶绿素电荷转移态的部分混合相关联。另一方面，猝灭态具有完全不同的性质，与非相干激发转移到短寿命类胡萝卜素激发态有关。我们的结果还表明，通过非常细微地改变转变为猝灭态的 LHCII 的数量，可以在体内实现所需的光保护水平。
