LOCALIZATION OF MEVALONATE PATHWAY AND NON-MEVALNATE PATHWAY

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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.