Zareb Herman

Biosynthesis of limonoids in Citrus: Sites and translocation

Abstract Sites of limonoid biosynthesis were located in Citrus limon . The stem was found to be the major site of nomilin biosynthesis from acetate. Epicotyl, hypocotyl and root tissues were also capable of biosynthesizing nomilin from acetate, but leaves, fruits and seeds did not show this capacity under the conditions used. All the tissues tested were capable of biosynthesizing other limonoids starting from nomilin. C. limon was capable of translocating nomilin from the stem to other sites.

Biosynthesis of obacunone from nomilin in Citrus limon

Abstract Radioactive tracer work showed that [14C]nomilin was converted to at least four metabolites in Citrus limon. One metabolite was identified as obacunone, showing that obacunone is biosynthesized from nomilin in C. limon.

Biosynthesis of limonoid glucosides in navel orange

Abstract Using radioactive tracers, nomilin was converted to nomilin 17-β- d -glucopyranoside in the mature albedo tissue of a navel orange. The reaction utilized UDP-glucose as a substrate. Application of 2-chloroethylphosphonic acid to small green navel oranges initiated the formation of limonoid glucosides in the fruit. Nomilin glucoside was not metabolized in the mature albedo tissue. The formation of limonoid glucosides represent a natural pathway for the debittering of citrus juices.

Limonoid biosynthesis in the stem of Citrus limon

Abstract Using radioactive tracer techniques, the phloem region of Citrus limon stems was shown to be the site of limonoid biosynthesis from acetate. The cortex and inner core regions were found incapable of biosynthesizing limonoids from acetate. However, all the regions were capable of biosynthesizing other limonoids starting from nomilin.

Limonin biosynthesis from obacunone via obacunoate in Citrus limon

Abstract Radioactive tracer work showed that [14C]obacunone was converted to at least four metabolites in Citrus limon. Two were identified as obacunoate and limonin. When [14C]methyl obacunoate was fed, limonin was found to be one of the metabolites. Based on these results and data accumulated thus far, biosynthetic pathways of limonoids in citrus are proposed.

Biosynthesis of limonoids: Conversion of deacetylnomilinate to nomilin in Citrus limon

Abstract Radioactive tracer work showed that deacetylnomilinate was converted to nomilin in detached stems of young Citrus limon seedlings. This work and the previous findings suggest that deacetylnomilinate is the initial limonoid to be biosynthesized among the limonoids known to be present in Citrus. Possible biosynthetic pathways for the formation of limonoids in Citrus are proposed.

Metabolism of limonoids: nomilin to nomilinate in citrus limon

Abstract Nomilinate was found to be the major acidic limonoid present in seedlings of Citrus limon . [ 14 C]Nomilin was converted to at least six acidic metabolites in C. limon , one of which was identified as nomilinate. The metabolism via nomilinate is the fifth metabolic pathway of nomilin shown to be present in nature.

Metabolism of limonoids in the citrus hybrid calamondin

Abstract Radioactive tracer work showed that in young seeding of calamondin decetylnomilinate was converted to nomilin, obacunone and 6-keteb-nomilol, a new lim

Phytohormone bioregulation of nomilin biosynthesis in Citrus limon seedlings

Abstract Auxins such as indoleacetic acid, indolebutyric acid, naphthaleneacetic acid and 2,4,5-trichlorophenoxyacetic acid were found to be potent inhibitors of nomilin biosynthesis in young seedlings of Citrus limon. Up to 97 % of the biosynthesis was inhibited. The auxins used were all effective and inhibited the biosynthesis of nomilin selectively. Abscisic acid was also a potent inhibitor of nomilin biosynthesis and the inhibition was reversed with a cytokinin. Gibberellic acid (GA3) had no effect on nomilin biosynthesis.

A limonoid from young calamondin seedlings

Abstract Radioactive tracer work resulted in the finding of a new limonoid in young seedlings of calamondin (Citrus reticulata cv. ‘Austera’ x Fortunella sp.). The compound was identified by NMR and TLC analyses as 6-keto-7β-deacetylnomilol.The results show that this compound was biosynthesized and accumulated during early stages of growth.