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Plastid Terminal oxidase (PTOX) and its physiological roles in carotenoid biosynthesis and in response eo stress in tomato

Maryam Shahbazi
Abstract : The plastid terminal oxidase (PTOX) is a plastoquinol oxidase whose absence in tomato results in the ghost (gh) phenotype characterized by variegated leaves (with bleached sectors accumulating phytoene) and by a carotenoid deficient ripe fruit. In order to elucidate the different roles of PTOX which have in common the modulation of plastoquinone redox states, various experimental conditions were applied. PTOX function in carotenoid biosynthesis, as a cofactor for phytoene desaturation, is essentially important at some developmental stage such as plastid de-etiolation or chromoplast differentiation. However, in low light, gh can produce adult green leaves and fruits containing similar carotenoids contents than in WT, without phytoene accumulation. Over-expression of an Arabidopsis PTOX cDNA in tomato did not lead to carotenoid over-production. While PTOX overproduction has minimal effects on photosynthesis, PTOX deficient green leaves and fruits have a reduced potential to prevent oxidative damage, as well as a higher PSII sensitivity to photoinhibition and damage. The absence of PTOX renders the tomato leaf photosynthetic apparatus more sensitive to light due to a nonphotochemical overreduction of plastoquinones in dark and high reduction state of the electron transport chain under steady state illumination. Thus, PTOX has an indispensable and direct role in photosynthesis, namely its influence on the redox status of the plastoquinone pool between PSII and PSI. Rather than contributing to an electron sink, PTOX has a global regulatory role in the distribution of electrons to different linear and alternative electron pathways, which is particularly important during dark to light and low light to high light transitions.
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Submitted on : Tuesday, September 20, 2011 - 4:58:04 PM
Last modification on : Tuesday, September 20, 2011 - 5:06:44 PM
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  • HAL Id : tel-00625094, version 1




Maryam Shahbazi. Plastid Terminal oxidase (PTOX) and its physiological roles in carotenoid biosynthesis and in response eo stress in tomato. Vegetal Biology. Université de Grenoble, 2008. English. ⟨tel-00625094⟩



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