title: Auxin-induced fruit-set in tomato is mediated in part by gibberellins.
abstract: Tomato (Solanum lycopersicum L.) fruit-set and growth depend on gibberellins (GAs). Auxins, another kind of hormone, can also induce parthenocarpic fruit growth in tomato, although their possible interaction with GAs is unknown. We showed that fruit development induced by the auxins indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid (2,4-D) were significantly reduced by the simultaneous application of inhibitors of GA biosynthesis, and that this effect was reversed by the application of GA(3). This suggested that the effect of auxin was mediated by GA. Parthenocarpic fruits induced by 2,4-D had higher levels of the active GA(1), its precursors and metabolites, than unpollinated non-treated ovaries, but similar levels as those found in pollinated ovaries. Application experiments of radioactive-labelled GAs to unpollinated ovaries showed than 2,4-D altered GA metabolism (both biosynthesis and catabolism) in vivo. Transcript levels of genes encoding copalyldiphosphate synthase (SlCPS), SlGA20ox1, SlGA20ox2 and SlGA20ox3, and SlGA3ox1 were higher in unpollinated ovaries treated with 2,4-D. In contrast, transcript levels of SlGA2ox2 (out of the five SlGA2ox genes known to encode this kind of GA-inactivating enzyme) were lower in ovaries treated with 2,4-D. Our results support the idea that auxins induce fruit-set and growth in tomato, at least partially, by enhancing GA biosynthesis (GA 20-oxidase, GA 3-oxidase and CPS), and probably by decreasing GA inactivation (GA2ox2) activity, thereby leading to higher levels of GA(1). The expression of diverse Aux/indole-3-acetic acid (IAA) and auxin response factors, which may be involved in this effect of auxin, was also altered in 2,4-D-induced ovaries.
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas (Universidad Politécnica de Valencia-CSIC), Valencia, Spain.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Serrani
authors.forename: Omar
authors.initials: O
authors.lastname: Ruiz-Rivero
authors.forename: Mariano
authors.initials: M
authors.lastname: Fos
authors.forename: José Luis
authors.initials: JL
authors.lastname: García-Martínez
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D005638:Fruit / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D018551:Solanum lycopersicum / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism; D018749:RNA, Plant / Q000378:metabolism; D014230:Triazoles / Q000494:pharmacology
chemical_list: D005875:Gibberellins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D018749:RNA, Plant; D014230:Triazoles; D015084:2,4-Dichlorophenoxyacetic Acid; C053370:paclobutrazol; C030737:indoleacetic acid