Journal Article

Development of an abscisic acid biosynthesizing cell-free system from flavedo of Citrus sinensis fruit

Gaynor R. Richardson and A. Keith Cowan

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 47, issue 3, pages 455-464
Published in print March 1996 | ISSN: 0022-0957
Published online March 1996 | e-ISSN: 1460-2431 | DOI: https://dx.doi.org/10.1093/jxb/47.3.455
Development of an abscisic acid biosynthesizing cell-free system from flavedo of Citrus sinensis fruit

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Cell-free extracts prepared from an acetone powder derived from the flavedo of mature, coloured fruits of Citrus sinensis L. cv. Midknight transformed mevalonic acid, isopentenyl pyrophosphate, all-trans-β-carotene and 1′ ,4′ -trans-ABAdiol into ABA. This is the first report of a cell-free system capable of producing ABA from both a terpenyl pyrophosphate and carotenoid origin. ABA biosynthesizing activity was stimulated by reduced nicotinamide nucleotides, molybdate, AM01618 and a cold-pool trap of (±)-ABA, but was inhibited by FAD. Addition of FAD caused accumulation of label from isopentenyl pyrophosphate in a compound with similar chromatographic and spectrophotometric properties to those of β-carotene. 1′,4′-Trans-ABAdiol, ABA and PA were unequivocally characterized as products of β-carotene metabolism in this cell-free system, a process that was markedly improved by extraction of enzyme in the presence of detergents. Dithiothreitol enhanced ABA biosynthesis from all-trans-β-carotene. Stigmasterol, and to a lesser extent cholesterol reduced conversion of β-carotene to ABA, but did not influence transformation of 1′,4′-trans-ABAdiol to ABA. AM01618 stimulated formation of ABA and appeared to exert its effect at the level of conversion of 1′,4′-trans-ABAdiol to ABA. Ancymidol and zeatin reduced incorporation of label from all-trans-β-carotene into ABA suggesting involvement of a mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kDa protein with peroxidase activity characteristic of a cytochrome P-450.

Keywords: Abscisic acid; biosynthesis; cell-free system Citrus sinensis; flavedo; Rutaceae

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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