26(C-2) 植物の2つのイソプレユニット生合成経路の役割 : 植物イソプレノイドの選択的かつ効率的なin vivo同位体標識法(口頭発表の部)

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Plants produce isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) as the common C_5-isoprenoid units through the plastidic methylerythritol phosphate (MEP) pathway and the cytosolic mevalonate (MVA) pathway. To assess which IPP/DMAPP pathways contribute for the biosynthesis of gibberellins (GAs), metabolites from each isoprenoid pathway were selectively labeled with <13>^C in Arabidopsis seedlings. Efficient <13>^C-labeling was achieved by blocking the endogenous pathway genetically or chemically during the feed of a <13>^C-labeled precursor specific to the MEP or MVA pathways. GC-MS analysis demonstrated that GAs are predominantly synthesized through the MEP pathway but also the MVA pathway partially contributed to GA biosynthesis in plants. Using our in vivo isoprenoid labeling system, the early stage of cytokinin (CK) biosynthesis in plants was next studied. LC-MS analysis demonstrated that the prenyl group of trans-zeatin (tZ) and isopentenyladenine mainly originates from the MEP pathway, whereas that of cis-zeatin is primarily biosynthesized through the MVA pathway. Plastid localization of four adenosine phosphates-isopentenyltransferases in Arabidopsis cells supported the idea that the MEP pathway primarily provides DMAPP to trans-zeatin and isopentenyladenine. To distinguish origins of the prenyl group of tZ-type CKs in TMR (Agrobacterial isopentenyltransferase)-introduced plants, we have prepared [3,4-<18>^O_2]1-deoxy-D-xylulose, which is incorporated into the MEP pathway to give [1-<18>^O]1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (a hydroxylated derivative of DMAPP and a possible direct precursor of prenyl group of tZ riboside monophosphate). We will present new findings from labeling experiments in Arabidopsis seedlings and Catharanthus cell cultures using this <18>^O-labeled precursor.
天然有機化合物討論会の論文
2004-10-01

26(C-2) 植物の2つのイソプレユニット生合成経路の役割 : 植物イソプレノイドの選択的かつ効率的なin vivo同位体標識法(口頭発表の部)

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