LOCALIZATION OF MEVALONATE PATHWAY AND NON-MEVALNATE PATHWAY

本研究旨在阐明苔藓植物胞内MVA生成叶绿体萜类的过程中famesyl diphosphate （FPP）衍生部分的优先标记机制，并证实这种非等效标记与质体内mevalate （MVA）途径（细胞质）和非MVA途径的定位存在剂量关系。在培养的角蒿（Anthoceros punctatus）和肝蒿（lintychanthus striatus）细胞中，MVA在肝蒿叶绿素a的植基侧链形成过程中普遍存在非等效标记。通过使用^2H和^<13> c标记的MVA和葡萄糖的掺入研究，证明了MVA和脱氧纤维素（DXP）途径同时参与植基侧链的生物合成。通过放射性前体的掺入，研究了肝草叶绿体对二磷酸异戊二酯的吸收。从这些研究中得到的结果总结如下。将二磷酸异戊二酯掺入平坦地鼠和斑纹地鼠的完整叶绿体中，表明地鼠叶绿体包膜对FPP的渗透性较高，而对IPP的渗透性较低。此外，随着二磷酸异戊二酯链长的增加，掺入GGOH的放射性也增加。因此，苔类植物中植基侧链的非等效标记可能是由胞浆中MVA生物合成的FPP选择性掺入叶绿体，并与内源性IPP进一步凝聚形成GGPP所致。因此，本研究为合理解释肝植物培养细胞中叶绿素a的植基侧链中fpp衍生部分优先标记的可能机制提供了证据。

The objectives of this research was to elucidate mechanism of the preferential labeling of the famesyl diphosphate (FPP)-derived portion in the formation of chloroplastidic terpenoids from MVA in cells of Bryophyta, and to confirm that this non-equivalent labeling has dose relation with localization of mevalonate (MVA) pathways hi cytosd and non-MVA pathway in plastids.Ubiquitous presence of non-equivalent labeling was observed in cultured cells of hornwort Anthoceros punctatus and liverwort, Ptychanthus striatus in the formation of the phytyl side-chain of chlorophyll a of the liverwort from MVA. The simultaneous involvement of MVA and deoxyxylulose (DXP) pathways for the phytyl side-chain biosynthesis was proven by incorporation study using ^2H and ^<13>C-labeled MVA and glucose. Uptake of isoprenyl diphosphates into liverwort chloroplasts was investigated by incorporation of radioactive precursors. The results obtained from these studies were summarized as follows.The incorporation of isoprenyl diphosphates using the intact chloroplasts from H. planus and P. striaaatus revealed that the chloroplast envelope of liverworts is highly permeable to FPP, while much less to IPP. In addition, as the chain length of the isoprenyl diphosphate increases, the radioactivity incorporated to the GGOH was also increased. Thus the non-equivalent labeling of the phytyl side-chain in liverworts has been possibly caused by selective incorporation of FPP into the chloroplasts, which is biosynthesized from MVA in cytosol, and its further condensation with endogenous IPP to form GGPP.Thus this study provides evidence for a rational explanation of possible mechanism for the preferential labeling in the FPP-derived portion of the phytyl side-chain of chlorophyll a in cultured cells of liverworts.