Peter Ou

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.

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.

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.

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.