Photosynthetic Pigment Localization and Thylakoid Membrane Morphology Are Altered in Synechocystis 6803 Phycobilisome Mutants
Photosynthetic Pigment Localization and Thylakoid Membrane Morphology Are Altered in Synechocystis 6803 Phycobilisome Mutants
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DOI：
10.1104/pp.111.192849
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发表时间：
2012-04-01
期刊：
影响因子：
7.4
通讯作者：
Timlin, Jerilyn A.
中科院分区：
文献类型：
--
作者：
Collins, Aaron M.;Liberton, Michelle;Timlin, Jerilyn A.
蓝藻是一种产氧光合原核生物，是藻类和植物叶绿体的前体。除了膜结合的含有叶绿素的蛋白质外，这些生物还使用大的膜-外源藻胆体天线来收集光线。与真核光合作用生物相似，蓝藻具有类囊体膜，其中含有光系统(PS)I和PS II，分别驱动水的氧化和NADP(+)的还原。虽然在一些品系的蓝藻中已经研究了类囊体的形态，但PSI和PSII在类囊体膜中的全球分布和捕光藻胆体的相应位置尚不清楚，这些信息对于在更大范围内理解蓝藻光合作用的功能是必要的。在这里，我们使用电子显微镜和高光谱共聚焦荧光显微镜相结合的方法，在野生型聚球藻PCC6803和一系列藻胆体逐渐被截断的突变体中解决了这个问题。我们发现，随着藻胆体天线的减小，类囊体形态发生了大规模的变化，并伴随着两个光系统物理分离的增加。最后，我们在每个细胞的基础上量化了来自两个光系统的体内发射强度，表明在突变体中PSI：PSII的比率逐渐降低。这既是由于光系统II的数量增加，也是由于光系统I的浓度降低。我们认为，这些变化是一种适应性策略，允许细胞在限光条件下平衡光系统I和II的光吸收能力。
Cyanobacteria are oxygenic photosynthetic prokaryotes that are the progenitors of the chloroplasts of algae and plants. These organisms harvest light using large membrane-extrinsic phycobilisome antenna in addition to membrane-bound chlorophyll-containing proteins. Similar to eukaryotic photosynthetic organisms, cyanobacteria possess thylakoid membranes that house photosystem (PS) I and PSII, which drive the oxidation of water and the reduction of NADP(+), respectively. While thylakoid morphology has been studied in some strains of cyanobacteria, the global distribution of PSI and PSII within the thylakoid membrane and the corresponding location of the light-harvesting phycobilisomes are not known in detail, and such information is required to understand the functioning of cyanobacterial photosynthesis on a larger scale. Here, we have addressed this question using a combination of electron microscopy and hyperspectral confocal fluorescence microscopy in wild-type Synechocystis species PCC 6803 and a series of mutants in which phycobilisomes are progressively truncated. We show that as the phycobilisome antenna is diminished, large-scale changes in thylakoid morphology are observed, accompanied by increased physical segregation of the two photosystems. Finally, we quantified the emission intensities originating from the two photosystems in vivo on a per cell basis to show that the PSI: PSII ratio is progressively decreased in the mutants. This results from both an increase in the amount of photosystem II and a decrease in the photosystem I concentration. We propose that these changes are an adaptive strategy that allows cells to balance the light absorption capabilities of photosystems I and II under light-limiting conditions.