<i>Scenedesmus obliquus</i> PS28: a tocopherol-free mutant which cannot form phytol

Henry, Alison; Powls, Roy; Pennock, J. F.

doi:10.1042/bst0140958

Cited by 14 publications

(8 citation statements)

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“…e-, electron; PQ, plastoquinone; PQH2, plastoquinol. Wong, 1974;Henry et al, 1986). These Scenedesmus mutants demonstrate clearly that tocopherols are not required for carotenoid synthesis, allowing us to conclude that plastoquinone is essential for phytoene desaturation in photosynthetic tissue.…”

Section: Quinones and Electron Transport Chains Provide A Unifying Mementioning

confidence: 90%

Genetic dissection of carotenoid synthesis in arabidopsis defines plastoquinone as an essential component of phytoene desaturation.

1995

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Carotenoids are C40 tetraterpenoids synthesized by nuclear-encoded multienzyme complexes located in the plastids of higher plants. To understand further the components and mechanisms involved in carotenoid synthesis, we screened Arabidopsis for mutations that disrupt this pathway and cause accumulation of biosynthetic intermediates. Here, we report the identification and characterization of two nonallelic albino mutations, pds1 and pds2 (for phytoene desaturation), that are disrupted in phytoene desaturation and as a result accumulate phytoene, the first C40 compound of the pathway. Surprisingly, neither mutation maps to the locus encoding the phytoene desaturase enzyme, indicating that the products of at least three loci are required for phytoene desaturation in higher plants. Because phytoene desaturase catalyzes an oxidation reaction, it has been suggested that components of an electron transport chain may be involved in this reaction. Analysis of pds1 and pds2 shows that both mutants are plastoquinone and tocopherol deficient, in addition to their inability to desaturate phytoene. Separate steps of the plastoquinone/tocopherol biosynthetic pathway are affected by these two mutations. The pds1 mutation affects the enzyme 4-hydroxyphenylpyruvate dioxygenase because it can be rescued by growth on the product but not the substrate of this enzyme, homogentisic acid and 4-hydroxyphenylpyruvate, respectively. The pds2 mutation most likely affects the prenyl/phytyl transferase enzyme of this pathway. Because tocopherol-deficient mutants in the green alga Scenedesmus obliquus can synthesize carotenoids, our findings demonstrate conclusively that plastoquinone is an essential component in carotenoid synthesis. We propose a model for carotenoid synthesis in photosynthetic tissue whereby plastoquinone acts as an intermediate electron carrier between carotenoid desaturases and the photosynthetic electron transport chain.

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Section: Quinones and Electron Transport Chains Provide A Unifying Mementioning

confidence: 90%

Genetic dissection of carotenoid synthesis in arabidopsis defines plastoquinone as an essential component of phytoene desaturation.

1995

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“…Both a-T and Chl contain a phytyl moiety as part of their molecule and both are biosynthesized within the chloroplast, although at different sites (19). The phytol utilized for their biosynthesis may be derived from a common pool-a Scenedesmus mutant which lacks the ability to reduce geranylgeraniol and form phytol did not contain a-T and did not have normal Chl (11). Administration of phytol has been shown to bring about a marked increased in the biosynthesis of a-T, in intact cells (5) as well as in in vitro systems (18) which seemed to have sufficient phytyl kinase activity ( 18).…”

Section: Discussionmentioning

confidence: 99%

Accumulation of α-Tocopherol in Senescing Organs as Related to Chlorophyll Degradation

Rise¹,

Cojocaru²,

Gottlieb³

et al. 1989

Plant Physiol.

108

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a-Tocopherol (a-T) has been identified, using gas chromatography-mass spectroscopy and 'H-and 13C-nuclear magnetic resonance, in senescing leaves of Melia azedarach L. The content of a-T increased concomitantly with the breakdown of chlorophyll in senescing Vinca and Melia leaves. An increase in a-T was found also in detached Melia leaves, senescing in either light or darkness and in senescing, ethylene-treated orange leaves and fruit. The possibility that phytol, which is released from chlorophyll by chlorophyllase is utilized for the biosynthesis of a-T is discussed. Senescing leaves of the low chlorophyllase plants, parsley and tobacco, did not contain a-T in measureable amounts.in Petri dishes containing moist filter paper covered with a Saran net, on which the leaves were laid to avoid direct contact with water. Dark green Melia leaflets, picked by late summer (September), were also allowed to senesce by the same method.Orange (Citrus sinensis L. Osbeck cv Shamouti) leaves and mature green fruit were harvested from the orchard and allowed to senesce in glass cylinders under a humid stream of air containing 20dl V-' of ethylene/L at 25C in the dark. ExtractionChl degradation occurs widely in nature as part of the senescence and ripening of green plant organs. The exact fate of the Chl molecule is not known, however (see Refs. 10 and 20 for recent reviews). Removal of the phytol by chlorophyllase has been suggested to be one of the earliest degradative steps, at least in certain plant species (2,14).Notwithstanding the progress made in recent years (13,16) further identification ofbreakdown intermediates seems to be the most important task for the elucidation of the pathway of Chl catabolism.In search for compounds which accumulate during the course of the disappearance of Chl we were intrigued by a peak in our HPLC system which eluted between Chl a and b and which increased markedly during senescence.In the present paper we report the identification of this peak as a-T' and the accumulation of this compound during senescence in several plant species. MATERIALS AND METHODS Plant MaterialLeaves ofMelia azedarach L., China tree, and Vinca major representing different degrees of senescence were collected from plants growing on campus during autumn. Leaves at different degrees of senescence were picked also from tobacco (Nicotiana tabacum L.) growing in pots in the greenhouse.Parsley (Petroselinum sativum L.) and celery (Apium graveolens L.) leaves were purchased fresh in the market. Leaves were allowed to senesce at 25°C either in light or in darkness, ' Abbreviation: a-T, a-tocopherol.Plant materials were homogenized with a Polytron homogenizer in -1 5°C acetone (0.2 g leaf tissue/5 mL; 0.5 g Citrus fruit peel/5 mL) and left in the cold for 10 min. The homogenate was centrifuged to remove the debris and the supernatant filtered through a 0.45 ,um pore size Millipore filter prior to analysis by HPLC. HPLC AnalysisAn LKB HPLC system equipped with a UV detector (Micromeritics 788) and HP3390 integrator w...

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“…A Scenedesmus mutant lacking all tocopherols has been reported (29), but the lesion in the mutant appeared to affect the synthesis of phylloquinones and phytylbenzoquinones in addition to tocopherols (74). The Arabidopsis pds1 and pds2 mutants lack both tocopherols and quinones due to blocks in the biosynthetic pathway common to both types of molecules (113).…”

Section: Antioxidant Moleculesmentioning

confidence: 99%

PHOTOPROTECTION REVISITED:Genetic and Molecular Approaches

Niyogi

1999

Annu. Rev. Plant. Physiol. Plant. Mol. Biol.

1,806

1,339

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The involvement of excited and highly reactive intermediates in oxygenic photosynthesis poses unique problems for algae and plants in terms of potential oxidative damage to the photosynthetic apparatus. Photoprotective processes prevent or minimize generation of oxidizing molecules, scavenge reactive oxygen species efficiently, and repair damage that inevitably occurs. This review summarizes several photoprotective mechanisms operating within chloroplasts of plants and green algae. The recent use of genetic and molecular biological approaches is providing new insights into photoprotection, especially with respect to thermal dissipation of excess absorbed light energy, alternative electron transport pathways, chloroplast antioxidant systems, and repair of photosystem II. CONTENTS

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Scenedesmus obliquus PS28: a tocopherol-free mutant which cannot form phytol

Cited by 14 publications

References 0 publications

Genetic dissection of carotenoid synthesis in arabidopsis defines plastoquinone as an essential component of phytoene desaturation.

Genetic dissection of carotenoid synthesis in arabidopsis defines plastoquinone as an essential component of phytoene desaturation.

Accumulation of α-Tocopherol in Senescing Organs as Related to Chlorophyll Degradation

PHOTOPROTECTION REVISITED:Genetic and Molecular Approaches

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