Physiological validation of photochemical reflectance index (PRI) as a photosynthetic parameter using Arabidopsis thaliana mutants
Physiological validation of photochemical reflectance index (PRI) as a photosynthetic parameter using Arabidopsis thaliana mutants
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DOI：
10.1016/j.bbrc.2018.02.192
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发表时间：
2018-03-25
影响因子：
3.1
通讯作者：
Hikosaka, Kouki
中科院分区：
文献类型：
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作者：
Kohzuma, Kaori;Hikosaka, Kouki
非光化学猝灭（NPQ）是高等植物最重要的光保护系统。根据叶绿素荧光达到稳态后弛缓的时间尺度，NPQ可分为几个步骤（即快相qE、中相qZ或qT、慢相qI）。在叶黄素循环过程中，多余能量作为热量的耗散，在快到中阶段（秒到分钟）可以检测到NPQ的很大一部分。虽然热耗散主要使用间接方法研究，如叶绿素a荧光测量，但这种分析需要暗适应或在测量期间应用饱和脉冲，因此难以连续监测这一过程。在这里，我们设计了一种基于光化学反射指数（PRI）的非常规技术，用于实时监测类囊体管腔pH的变化（通过叶黄素色素含量的变化来反映），我们通过测量531 nm处的光驱动叶片反射率来估计PRI。为了揭示PRI的调控因子，我们分析了两个拟南芥突变体npql（由于紫黄质去环氧化酶（VDE）活性受到抑制而无法将紫黄质转化为玉米黄质）和npq4（缺乏PsbS蛋白）。在野生型和npq4中，PRI是可变的，而在npql中则没有，这表明PRI与叶黄素循环依赖的热能猝灭（qZ）有关，而不是与线性电子传递速率或NPQ有关。使用pH控制缓冲溶液进行原位管腔pH替换导致PRI发生变化。这些结果表明PRI仅反映叶黄素循环转换，因此是监测体内类囊体管腔pH（反映VDE活性）的有用参数。(C) 2018年作者。Elsevier Inc.出版。
Non-photochemical quenching (NPQ) is the most important photoprotective system in higher plants. NPQ can be divided into several steps according to the timescale of relaxation of chlorophyll fluorescence after reaching a steady state (i.e., the fast phase, qE; middle phase, qZ or qT; and slow phase, qI). The dissipation of excess energy as heat during the xanthophyll cycle, a large component of NPQ is detectable during the fast to middle phase (sec to min). Although thermal dissipation is primarily investigated using indirect methods such as chlorophyll a fluorescence measurements, such analyses require dark adaptation or the application of a saturating pulse during measurement, making it difficult to continuously monitor this process. Here, we designed an unconventional technique for real-time monitoring of changes in thylakoid lumen pH (as reflected by changes in xanthophyll pigment content) based on the photochemical reflectance index (PRI), which we estimated by measuring light-driven leaf reflectance at 531 nm. We analyzed two Arabidopsis thaliana mutants, npql (unable to convert violaxanthin to zeaxanthin due to inhibited violaxanthin de-epoxidase [VDE] activity) and npq4 (lacking PsbS protein), to uncover the regulator of the PRI. The PRI was variable in wild-type and npq4 plants, but not in npql, indicating that the PRI is related to xanthophyll cycle-dependent thermal energy quenching (qZ) rather than the linear electron transport rate or NPQ. In situ lumen pH substitution using a pH-controlled buffer solution caused a shift in PRI. These results suggest that the PRI reflects only xanthophyll cycle conversion and is therefore a useful parameter for monitoring thylakoid lumen pH (reflecting VDE activity) in vivo. (C) 2018 The Authors. Published by Elsevier Inc.