Sato N, Hagio M, Wada H, Tsuzuki M
School of Life Science, Tokyo University of Pharmacy and Life Science, Horinouchi, Hachioji, Tokyo 192-0392, Japan.
Proc Natl Acad Sci U S A. 2000 Sep 12;97(19):10655-60. doi: 10.1073/pnas.97.19.10655.
To investigate the role of phosphatidylglycerol (PG) in photosynthesis, we constructed a mutant defective in the CDP-diacylglycerol synthase gene from a cyanobacterium, Synechocystis sp. PCC6803. The mutant, designated as SNC1, required PG supplementation for growth. Growth was repressed in PG-free medium concomitantly with the decrease in cellular content of PG. These results indicate that PG is essential, and that SNC1 is defective in PG synthesis. Decrease in PG content was accompanied by a reduction in the cellular content of chlorophyll, but with little effect on the contents of phycobilisome pigments, which showed that levels of chlorophyll-protein complexes decreased without alteration of those of phycobilisomes. Regardless of the decrease in the PG content, CO(2)-dependent photosynthesis by SNC1 was similar to that by the wild type on a chlorophyll basis, but consequently became lower on a cell basis. Simultaneously, the ratio of oxygen evolution of photosystem II (PSII) measured with p-benzoquinone to that of CO(2)-dependent photosynthesis, which ranged between 1.3 and 1.7 in the wild type. However, it was decreased in SNC1 from 1.3 to 0.4 during the early growth phase where chlorophyll content and CO(2)-dependent photosynthesis were little affected, and then finally to 0.1, suggesting that PSII first lost its ability to reduce p-benzoquinone and then decreased in its level and actual activity. These results indicate that PG contributes to the accumulation of chlorophyll-protein complexes in thylakoid membranes, and also to normal functioning of PSII.
为了研究磷脂酰甘油（PG）在光合作用中的作用，我们构建了一个来自蓝藻集胞藻PCC6803的CDP - 二酰甘油合成酶基因缺陷型突变体。该突变体命名为SNC1，其生长需要补充PG。在无PG培养基中生长受到抑制，同时细胞内PG含量降低。这些结果表明PG是必需的，且SNC1在PG合成方面存在缺陷。PG含量的降低伴随着叶绿素细胞含量的减少，但对藻胆体色素含量影响不大，这表明叶绿素 - 蛋白复合物水平降低，而藻胆体水平未改变。尽管PG含量降低，但基于叶绿素的基础上，SNC1的CO₂依赖性光合作用与野生型相似，但基于细胞的基础上则较低。同时，用对苯醌测量的光系统II（PSII）放氧与CO₂依赖性光合作用的比率，在野生型中为1.3至1.7。然而，在SNC1中，在早期生长阶段，当叶绿素含量和CO₂依赖性光合作用几乎不受影响时，该比率从1.3降至0.4，最终降至0.1，这表明PSII首先失去还原对苯醌的能力，然后其水平和实际活性降低。这些结果表明PG有助于类囊体膜中叶绿素 - 蛋白复合物的积累，也有助于PSII的正常功能。
