title: Dual role of the plastid terminal oxidase in tomato.
abstract: The plastid terminal oxidase (PTOX) is a plastoquinol oxidase whose absence in tomato (Solanum lycopersicum) results in the ghost (gh) phenotype characterized by variegated leaves (with green and bleached sectors) and by carotenoid-deficient ripe fruit. We show that PTOX deficiency leads to photobleaching in cotyledons exposed to high light primarily as a consequence of reduced ability to synthesize carotenoids in the gh mutant, which is consistent with the known role of PTOX as a phytoene desaturase cofactor. In contrast, when entirely green adult leaves from gh were produced and submitted to photobleaching high light conditions, no evidence for a deficiency in carotenoid biosynthesis was obtained. Rather, consistent evidence indicates that the absence of PTOX renders the tomato leaf photosynthetic apparatus more sensitive to light via a disturbance of the plastoquinone redox status. Although gh fruit are normally bleached (most likely as a consequence of a deficiency in carotenoid biosynthesis at an early developmental stage), green adult fruit could be obtained and submitted to photobleaching high light conditions. Again, our data suggest a role of PTOX in the regulation of photosynthetic electron transport in adult green fruit, rather than a role principally devoted to carotenoid biosynthesis. In contrast, ripening fruit are primarily dependent on PTOX and on plastid integrity for carotenoid desaturation. In summary, our data show a dual role for PTOX. Its activity is necessary for efficient carotenoid desaturation in some organs at some developmental stages, but not all, suggesting the existence of a PTOX-independent pathway for plastoquinol reoxidation in association with phytoene desaturase. As a second role, PTOX is implicated in a chlororespiratory mechanism in green tissues.
authors.affiliation: Centre National de la Recherche Scientifique and Université Joseph Fourier, Laboratory Plastes et Différenciation Cellulaire, 38041 Grenoble, France.
authors.forename: Maryam
authors.initials: M
authors.lastname: Shahbazi
authors.forename: Matthias
authors.initials: M
authors.lastname: Gilbert
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Labouré
authors.forename: Marcel
authors.initials: M
authors.lastname: Kuntz
mesh_terms: D002338:Carotenoids; D018548:Cotyledon / Q000378:metabolism / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport; D008027:Light; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D009154:Mutation; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D013997:Time Factors
chemical_list: D002338:Carotenoids; D010088:Oxidoreductases