Havaux Michel, Dall'Osto Luca, Cuiné Stephan, Giuliano Giovanni, Bassi Roberto
CEA/Cadarache, DSV, DEVM, Laboratoire d'Ecophysiologie de la Photosynthèse, UMR 163 CEA-CNRS, Université Méditérranée-CEA 1000, F-13108 Saint-Paul-lez-Durance, France.
J Biol Chem. 2004 Apr 2;279(14):13878-88. doi: 10.1074/jbc.M311154200. Epub 2004 Jan 13.
In green plants, the xanthophyll carotenoid zeaxanthin is synthesized transiently under conditions of excess light energy and participates in photoprotection. In the Arabidopsis lut2 npq2 double mutant, all xanthophylls were replaced constitutively by zeaxanthin, the only xanthophyll whose synthesis was not impaired. The relative proportions of the different chlorophyll antenna proteins were strongly affected with respect to the wild-type strain. The major antenna, LHCII, did not form trimers, and its abundance was strongly reduced as was CP26, albeit to a lesser extent. In contrast, CP29, CP24, LHCI proteins, and the PSI and PSII core complexes did not undergo major changes. PSII-LHCII supercomplexes were not detectable while the PSI-LHCI supercomplex remained unaffected. The effect of zeaxanthin accumulation on the stability of the different Lhc proteins was uneven: the LHCII proteins from lut2 npq2 had a lower melting temperature as compared with the wild-type complex while LHCI showed increased resistance to heat denaturation. Consistent with the loss of LHCII, light-state 1 to state 2 transitions were suppressed, the photochemical efficiency in limiting light was reduced and photosynthesis was saturated at higher light intensities in lut2 npq2 leaves, resulting in a photosynthetic phenotype resembling that of high light-acclimated leaves. Zeaxanthin functioned in vivo as a light-harvesting accessory pigment in lut2 npq2 chlorophyll antennae. As a whole, the in vivo data are consistent with the results obtained by using recombinant Lhc proteins reconstituted in vitro with purified zeaxanthin. While PSII photoinhibition was similar in wild type and lut2 npq2 exposed to high light at low temperature, the double mutant was much more resistant to photooxidative stress and lipid peroxidation than the wild type. The latter observation is consistent with an antioxidant and lipid protective role of zeaxanthin in vivo.
在绿色植物中，叶黄素类胡萝卜素玉米黄质在光能过剩的条件下短暂合成，并参与光保护过程。在拟南芥lut2 npq2双突变体中，所有叶黄素都被玉米黄质组成型取代，玉米黄质是唯一合成未受损害的叶黄素。与野生型菌株相比，不同叶绿素天线蛋白的相对比例受到强烈影响。主要天线LHCII不形成三聚体，其丰度大幅降低，CP26也是如此，尽管程度较小。相比之下，CP29、CP24、LHCI蛋白以及PSI和PSII核心复合物没有发生重大变化。未检测到PSII-LHCII超复合物，而PSI-LHCI超复合物未受影响。玉米黄质积累对不同Lhc蛋白稳定性的影响并不均匀：与野生型复合物相比，lut2 npq2的LHCII蛋白具有较低的解链温度，而LHCI对热变性的抗性增强。与LHCII的缺失一致，lut2 npq2叶片中光状态1到状态2的转变受到抑制，在低光条件下的光化学效率降低，光合作用在较高光强下达到饱和，从而导致类似于高光适应叶片的光合表型。在lut2 npq2叶绿素天线中，玉米黄质在体内作为一种光捕获辅助色素发挥作用。总体而言，体内数据与使用体外纯化的玉米黄质重组的重组Lhc蛋白所获得的结果一致。虽然野生型和lut2 npq2在低温高光条件下的PSII光抑制相似，但双突变体比野生型对光氧化应激和脂质过氧化的抗性要强得多。后一观察结果与玉米黄质在体内的抗氧化和脂质保护作用一致。
