Tardy F, Havaux M
Département d'Ecophysiologie Végétale et de Microbiologie, CEA, Centre d'Etudes de Cadarache, Saint-Paul-lez-Durance, France.
J Photochem Photobiol B. 1996 Jun;34(1):87-94. doi: 10.1016/1011-1344(95)07272-1.
The abscisic-acid-deficient aba-1 mutant of Arabidopsis thaliana is unable to epoxidize zeaxanthin. As a consequence, it contains large amounts of this carotenoid and lacks epoxy-xanthophylls. HPLC analysis of pigment contents in leaves, isolated thylakoids and preparations of the major light-harvesting complex of photosystem II (PSII) (LHC-II) indicated that zeaxanthin replaced neoxanthin, violaxanthin and antheraxanthin in the light-harvesting system of PSII in aba-1. Non-denaturing electrophoretic fractionation of solubilized thylakoids showed that the xanthophyll imbalance in aba-1 was associated with a pronounced decrease in trimeric LHC-II in favour of monomeric complexes, with a substantial increase in free pigments (mainly zeaxanthin and chlorophyll b), suggesting a decreased stability of LHC-II. The reduced thermostability of PSII in aba-1 was also deduced from in vivo chlorophyll fluorescence measurements. Wild-type and aba-1 leaves could not be distinguished on the basis of their photosynthetic performance: no significant difference was observed between the two types of leaves for light-limited and light-saturated photosynthetic oxygen evolution, PSII photochemistry and PSII to PSI electron flow. When dark-adapted leaves (grown in white light of 80 mumol m-2s-1) were suddenly exposed to red light of 150 mumol m-2s-1, there was a strong nonphotochemical quenching of chlorophyll fluorescence, the amplitude of which was virtually identical (at steady state) in aba-1 and wild-type leaves, despite the fact that the xanthophyll cycle pigment pool was completely in the form of zeaxanthin in aba-1 and almost exclusively in the form of violaxanthin in the wild type. A high concentration of zeaxanthin in aba-1 thylakoids did not, in itself, provide any particular protection against the photoinhibition of PSII. Taken together, the presented results indicate the following: (1) zeaxanthin can replace epoxy-xanthophylls in LHC-II without significantly affecting the photochemical efficiency of PSII; (2) zeaxanthin does not play any specific role in direct (thermal) energy dissipation in PSII; (3) the photoprotective action of the xanthophyll cycle (rapid photoconversion of violaxanthin to zeaxanthin) is not based on the mere substitution of violaxanthin by zeaxanthin in the chlorophyll antennae.
拟南芥中脱落酸缺陷型aba - 1突变体无法将玉米黄质环氧化。因此，它含有大量这种类胡萝卜素，且缺乏环氧叶黄素。对叶片、分离的类囊体以及光系统II（PSII）主要捕光复合体（LHC - II）制剂中的色素含量进行高效液相色谱分析表明，在aba - 1中，玉米黄质在PSII的捕光系统中取代了新黄质、紫黄质和花药黄质。对溶解的类囊体进行非变性电泳分级分离显示，aba - 1中叶黄素失衡与三聚体LHC - II显著减少、有利于单体复合体形成以及游离色素（主要是玉米黄质和叶绿素b）大量增加有关，这表明LHC - II的稳定性降低。aba - 1中PSII热稳定性降低也可从体内叶绿素荧光测量结果推断出来。野生型和aba - 1叶片在光合性能方面无法区分：在光限制和光饱和光合放氧、PSII光化学以及PSII到PSI的电子流方面，两种类型的叶片之间未观察到显著差异。当暗适应叶片（在80 μmol m⁻² s⁻¹的白光下生长）突然暴露于150 μmol m⁻² s⁻¹的红光下时，叶绿素荧光出现强烈的非光化学猝灭，尽管aba - 1中叶黄素循环色素库完全以玉米黄质形式存在，而野生型几乎完全以紫黄质形式存在，但在aba - 1和野生型叶片中，其幅度在稳态时几乎相同。aba - 1类囊体中高浓度的玉米黄质本身并未对PSII的光抑制提供任何特殊保护。综上所述，所呈现的结果表明：（1）玉米黄质可以在LHC - II中取代环氧叶黄素，而不会显著影响PSII的光化学效率；（2）玉米黄质在PSII的直接（热）能量耗散中不发挥任何特定作用；（3）叶黄素循环（紫黄质快速光转化为玉米黄质）的光保护作用并非仅仅基于叶绿素天线中玉米黄质对紫黄质的取代。
