Accumulation of menaquinones with incompletely reduced side chains and loss of alpha-tocopherol in rice mutants with alternations in the chlorophyll moiety.
Accumulation of menaquinones with incompletely reduced side chains and loss of alpha-tocopherol in rice mutants with alternations in the chlorophyll moiety.
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DOI：
10.1093/jxb/erh218
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发表时间：
2004-09
影响因子：
6.9
通讯作者：
M. Shibata;M. Tsuyama;Tsuneaki Takami;H. Shimizu;Y. Kobayashi
中科院分区：
文献类型：
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作者：
M. Shibata;M. Tsuyama;Tsuneaki Takami;H. Shimizu;Y. Kobayashi
水稻突变体M249和M134积累了叶绿素a和b，它们被不完全还原的醇如香叶基香叶醇、二氢香叶基香叶醇和四氢香叶基香叶醇酯化。在柱后化学还原将醌转化为荧光醌醇后，通过带有荧光检测器的高效液相色谱（HPLC）测定这些突变体叶子中α-生育酚、叶绿醌和甲基萘醌的含量。通过 HPLC 分析，在水稻突变体的叶段中检测到侧链还原状态不同的甲基萘醌（甲基萘醌），对植物醌具有高选择性和敏感性。突变体M249优先积累甲基萘醌，其侧链含有四氢香叶基香叶醇。然而，突变体M134表现出具有香叶基香叶醇侧链的甲基萘醌的优先积累。在两种突变体中，具有不同异戊二烯基侧链的甲基萘醌的积累模式与具有相应异戊二烯基侧链的叶绿素的积累模式相似。在叶绿素和鲜重基础上，野生型中光系统 I 主要电子供体 P700 的含量高于任一突变体。然而，野生型和突变体中总甲基萘醌与 P700 的比率相似。由于野生型和突变体之间的光合活性不存在比较大的差异，这些结果表明甲基萘醌侧链氢化成植醇并不是其在光系统I中充当电子受体的必要条件。另一方面，在野生型完全发育的叶子中检测到α-生育酚，但在突变体的叶子中未检测到。突变体叶片中甲基萘醌的积累和α-生育酚的损失表明叶绿素-香叶基香叶醇还原为植醇以及香叶基香叶基焦磷酸还原为植基焦磷酸是由相同的酶催化的。
The rice mutants M249 and M134 accumulate chlorophyllides a and b which are esterified with incompletely reduced alcohols such as geranylgeraniol, dihydrogeranylgeraniol, and tetrahydrogeranylgeraniol. Quantities of alpha-tocopherol, phylloquinone, and menaquinones in leaves of these mutants were determined by high performance liquid chromatography (HPLC) with a fluorescence detector after post-column chemical reduction to convert quinones to fluorescent quinols. Methylnaphthoquinones, varying in the reduction state of the side chain (menaquinones), were detected in leaf segments of the rice mutants on HPLC analyses with both high selectivity and sensitivity to plant quinones. Mutant M249 preferentially accumulated menaquinone, which contains tetrahydrogeranylgeraniol as its side chain. However, mutant M134 exhibited preferential accumulation of menaquinone with a geranylgeraniol side chain. In both mutants, the accumulation patterns of menaquinones with different prenyl side chains were similar to those of chlorophyll with the corresponding prenyl side chains. The content of P700, the photosystem I primary electron donor, in the wild type was greater than that of either mutant, on both a chlorophyll and a fresh weight basis. However, the ratios of total methylnaphthoquinones to P700 were similar in both the wild type and the mutants. Since no comparative large differences in photosynthetic activity exist between the wild type and the mutants, these results suggest that the hydrogenation of the methylnaphthoquinone side chain to phytol is not an essential requirement for it to function as an electron acceptor in photosystem I. On the other hand, alpha-tocopherol was detected in fully developed leaves of the wild type, but not in those of the mutants. Accumulation of menaquinones and the loss of alpha-tocopherol in mutant leaves suggest that the reduction of chlorophyll-geranylgeraniol to phytol and that of geranylgeranyl pyrophosphate to phytyl pyrophosphate are catalysed by the same enzyme.