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Published on September 14, 2007; 10.1104/pp.107.106336

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Received July 26, 2007
Accepted September 10, 2007

The Dual Role of the Plastid Terminal Oxidase (PTOX) in Tomato

Maryam Shahbazi , Matthias Gilbert , Anne-Marie Labouré , and Marcel Kuntz *

CNRS and Université Joseph Fourier, Laboratory Plastes et Différenciation Cellulaire, BP53, 38041 Grenoble, France; Universität Leipzig, Institut für Biologie I, Pflanzenphysiologie, Johannisallee 21-23, D-04103 Leipzig, Germany

* Corresponding author; email: marcel.kuntz{at}ujf-grenoble.fr.

The plastid terminal oxidase (PTOX) is a plastoquinol oxidase whose absence in tomato results in the ghost phenotype characterized by variegated leaves (with green and bleached sectors) and by a 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 ghost mutant, which is consistent with the known role of PTOX as a phytoene desaturase cofactor. In contrast, when entirely green adult leaves from ghost 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 PQ redox status. Although ghost 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.




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[Abstract] [Full Text] [PDF]


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