Beyond Non-Photochemical Fluorescence Quenching: The Overlapping Antioxidant Functions of Zeaxanthin and Tocopherols
Beyond Non-Photochemical Fluorescence Quenching: The Overlapping Antioxidant Functions of Zeaxanthin and Tocopherols
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DOI：
10.1007/978-94-017-9032-1_26
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发表时间：
2014-01-01
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影响因子：
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通讯作者：
Ignacio Garcia-Plazaola, Jose
中科院分区：
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作者：
Havaux, Michel;Ignacio Garcia-Plazaola, Jose
生育酚存在于所有光合真核生物的质体中，长期以来被认为是光保护防御的关键成分。膜结合生育酚通过猝灭单线态氧并通过其自由基清除活性防止脂质过氧化的传播而发挥重要的抗氧化作用。然而，用生育酚缺乏的植物进行的实验已经显示出高光照的令人惊讶的低影响，这显然是生育酚与玉米黄质（Z）的功能重叠的结果。除了玉米黄质在调节热耗散中的作用（通过叶绿素荧光的非光化学猝灭，NPQ评估），玉米黄质分子作为游离色素溶解在膜脂质相中或存在于脂质-蛋白质界面处，可以作为直接抗氧化剂和膜稳定剂，与生育酚具有协同效应。未结合的玉米黄质池的存在是由众多的应力实验，显示出更高的增强的总池的紫黄质-花药黄质-玉米黄质（VAZ）循环色素比其潜在的结合位点在天线蛋白。生育酚含量也受到强烈的环境调制的压力因素，生育酚和Z池的动态往往高度相关。然而，叶生育酚池的一个显着的比例积累在质体中，而不是类囊体，在那里它的保护作用并不那么清楚。从进化的角度来看，似乎有一个趋势，从藻类的叶黄素循环为基础的光保护陆生植物的一个更多样化的战略。
Tocopherols, present in plastids from all lineages of photosynthetic eukaryotes, have long been recognized as key constituents of photoprotective defenses. Membrane-bound tocopherols play an essential antioxidant role by quenching singlet oxygen and preventing the propagation of lipid peroxidation through their radical scavenging activity. However, experiments with tocopherol-deficient plants have shown a surprisingly low impact of high light, and this apparently is the result of a functional overlap of tocopherol with zeaxanthin (Z). Apart from the role of zeaxanthin in the modulation of thermal dissipation (assessed via non-photochemical quenching of chlorophyll fluorescence, NPQ), zeaxanthin molecules dissolved as free pigments in the membrane lipid phase or present at the lipid-protein interfaces may act as direct antioxidants and membrane stabilizers, having a synergistic effect with tocopherol. The existence of pools of unbound zeaxanthin is supported by numerous stress experiments that showed a much higher enhancement of the total pool of violaxanthin-antheraxanthin-zeaxanthin (VAZ) cycle pigments than that of their potential binding sites in antenna proteins. Tocopherol content is also subject to strong environmental modulation by stress factors, and the dynamics of the tocopherol and Z pools are frequently highly correlated. However, a significant proportion of the leaf tocopherol pool accumulates in plastoglobules, instead of thylakoids, where its protective role is not so clearly established. From an evolutionary perspective, there seems to be a trend from a xanthophyll cycle-based photoprotection in algae to a more diversified strategy in terrestrial plants.