pheophytin-a and isopentenyl-pyrophosphate

Transgenic plants of Arabidopsis thaliana (L.) Heynh. (ecotype Columbia) expressing the antisense AtMECT gene, encoding 2- C-methyl- D-erythritol 4-phosphate cytidylyltransferase, were generated to elucidate the physiological role of the nonmevalonate pathway for production of ent-kaurene, the latter being the plastidic precursor of gibberellins. In transformed plants pigmentation and accumulation of ent-kaurene were reduced compared to wild-type plants. Fosmidomycin, an inhibitor of 1-deoxy- D-xylulose 5-phosphate reductoisomerase (DXR), caused a similar depletion of these compounds in transgenic plants. These observations suggest that both AtMECT and DXR are important in the synthesis of isopentenyl diphosphate and dimethylallyl diphosphate and that ent-kaurene is mainly produced through the nonmevalonate pathway in the plastid.

Topics: Aldose-Ketose Isomerases; Arabidopsis; Carotenoids; Chlorophyll; Chlorophyll A; Chloroplasts; Cloning, Molecular; Diterpenes; Diterpenes, Kaurane; DNA, Antisense; Fosfomycin; Hemiterpenes; Mevalonic Acid; Molecular Sequence Data; Multienzyme Complexes; Nucleotidyltransferases; Organophosphorus Compounds; Oxidoreductases; Phenotype; Pigments, Biological; Plants, Genetically Modified

Callus cultures of the hornwort Anthoceros punctatus were induced from the apical portions of the gametophytes. Calli can accumulate rosmarinic acid, which is suggested as an intermediate for anthocerotonic acid, a rare phenylpropanoid dimer with a cyclobutane ring, indicating that calli possess the ability to produce secondary metabolites found primarily in intact plants. Biosynthesis of chloroplastidic terpenoids of liverworts showed preferential labeling of the farnesyl diphosphate (FPP)-derived portion in the phytyl side chain of chlorophyll a (1) when calli of A. punctatus are incubated with (2)H- and (13)C-labeled mevalonate. This finding suggests either that cytoplasmic FPP (or isopentenyl diphosphate, IPP) is taken into chloroplasts and condensed with endogenous IPP derived from a nonmevalonate pathway, or that FPP is synthesized within chloroplasts from extraplastidically formed IPP (or mevalonate) and then condensed with endogenous IPP in a different subplastidic fraction.

Topics: Antioxidants; Chlorophyll; Chlorophyll A; Chromatography, Agarose; Chromatography, High Pressure Liquid; Chromatography, Liquid; Cinnamates; Depsides; Hemiterpenes; Isotope Labeling; Magnetic Resonance Spectroscopy; Mevalonic Acid; Optical Rotation; Organophosphorus Compounds; Plants; Polyisoprenyl Phosphates; Rosmarinic Acid; Sesquiterpenes