Kaňa Radek
Institute of Microbiology, Academy of Sciences of the CzechiaTřeboň, Czechia; Faculty of Science, Institute of Chemistry and Biochemistry, University of South BohemiaČeské Budějovice, Czechia.
Center of Biophysics and Quantitative Biology, Department of Biochemistry, Department of Plant Biology, University of Illinois at Urbana-Champaign Urbana, IL, USA.
Front Plant Sci. 2016 Dec 16;7:1849. doi: 10.3389/fpls.2016.01849. eCollection 2016.
Regulation of photosynthetic light harvesting in the thylakoids is one of the major key factors affecting the efficiency of photosynthesis. Thylakoid membrane is negatively charged and influences both the structure and the function of the primarily photosynthetic reactions through its electrical double layer (EDL). Further, there is a heterogeneous organization of soluble ions (K, Mg, Cl) attached to the thylakoid membrane that, together with fixed charges (negatively charged amino acids, lipids), provides an electrical field. The EDL is affected by the valence of the ions and interferes with the regulation of "state transitions," protein interactions, and excitation energy "spillover" from Photosystem II to Photosystem I. These effects are reflected in changes in the intensity of chlorophyll fluorescence, which is also a measure of photoprotective non-photochemical quenching (NPQ) of the excited state of chlorophyll . A triggering of NPQ proceeds via lumen acidification that is coupled to the export of positive counter-ions (Mg, K) to the stroma or/and negative ions (e.g., Cl) into the lumen. The effect of protons and anions in the lumen and of the cations (Mg, K) in the stroma are, thus, functionally tightly interconnected. In this review, we discuss the consequences of the model of EDL, proposed by Barber (1980b) Biochim Biophys Acta :253-308) in light of light-harvesting regulation. Further, we explain differences between electrostatic screening and neutralization, and we emphasize the opposite effect of monovalent (K) and divalent (Mg) ions on light-harvesting and on "screening" of the negative charges on the thylakoid membrane; this effect needs to be incorporated in all future models of photosynthetic regulation by ion channels and transporters.
类囊体中光合光捕获的调节是影响光合作用效率的主要关键因素之一。类囊体膜带负电荷，并通过其双电层（EDL）影响主要光合反应的结构和功能。此外，类囊体膜上附着有可溶性离子（K、Mg、Cl）的异质组织，这些离子与固定电荷（带负电荷的氨基酸、脂质）一起形成了一个电场。双电层受离子价态的影响，并干扰“状态转换”、蛋白质相互作用以及从光系统II到光系统I的激发能“溢出”的调节。这些效应反映在叶绿素荧光强度的变化上，叶绿素荧光强度也是叶绿素激发态光保护非光化学猝灭（NPQ）程度的一种度量。NPQ的触发是通过内腔酸化进行的，内腔酸化与正抗衡离子（Mg、K）向基质的输出或/和负离子（如Cl）向内腔的输入相耦合。因此内腔中质子和阴离子以及基质中阳离子（Mg、K）的作用在功能上紧密相连。在本综述中，我们根据光捕获调节讨论了Barber（1980b，《生物化学与生物物理学报》：253 - 308）提出的双电层模型的结果。此外，我们解释了静电屏蔽和中和之间的差异，并强调了单价（K）和二价（Mg）离子在光捕获以及类囊体膜上负电荷“屏蔽”方面的相反作用；在未来所有关于离子通道和转运体对光合作用调节的模型中都需要考虑这种作用。
