【正文】 本科畢業(yè)設(shè)計（論文）外文翻譯 12 原文二 ： Carotenoid Biosynthesis during Tomato Fruit Development (Evidence for TissueSpecific Gene Expression) American Society of Plant Biologists. Plant Physiology. 1994, 105(1): 405~413. Tomato (Lycopersicon escμLentum Mill. cv Ailsa Craig) fruit, at five stages of development, have been analyzed for their carotenoid and chlorophyll (Chl) contents, in vitro activities of phytoene synthase, phytoene desaturase, and lycopene cyclase, as well as expression of the phytoene synthase (Psy) and phytoene desaturase (Pds) genes. During ripening, the total carotenoids increased with a conitant decrease in Chl. Although the highest carotenoid content (consisting mainly of lycopene and [beta]carotene) was found in ripe fruit, the greatest carotenogenic enzymic activities were found in green fruit. Phytoene synthase was located in the plastid stroma, whereas the metabolism of phytoene was associated with plastid membranes during all stages of fruit development. The in vitro products of phytoene desaturation altered from being predominantly phytofluence and [zeta]carotene in chloroplasts to being mainly lycopene in chromoplasts. The expression of Psy was detected in breaker and ripe fruit, as well as flowers, but was not detectable by northern blot analysis in leaves or green fruits. The Pds gene transcript was barely detectable in green fruit and leaves but was expressed in flowers and breaker fruit. These resμLts suggest that transcription of Psy and Pds is regμLated developmentally, with expression being considerably elevated in chromoplastcontaining tissues. Antiserum to the Synechococcus phytoene synthase crossreacted with phytoene synthase of green fruit only on western blots and not with the enzyme from ripe fruit. In contrast, a monoclonal antibody to the Psy gene product only crossreacted with phytoene synthase from ripe fruit. The enzymes from green and ripe fruit had different molecμLar masses of 42 and 38 kD, respectively. The absence of detectable Psy and Pds mRNA in green tissues using northern blot analyses, despite high levels of phytoene synthase and desaturase activity, lends support to the hypothesis of divergent genes encoding these enzymes. 。來自成熟和未成熟果實的酶的分子質(zhì)量不同，分別是 42 kD和 38 kD。 藍(lán)球菌八氫番茄紅素合成酶的抗血 清能與綠色果實的 八氫番茄紅素合成酶雜交，但不能與成熟果實的 PSY發(fā)生作用。 PDS基因在葉和綠色果實中沒有表達(dá)，而在花和果實破色期中檢測到。在色素細(xì)胞中八氫番茄紅素的體外產(chǎn)物顏色有所改變是由于在葉綠體中的 β胡蘿卜素大部分地轉(zhuǎn)化成番茄紅素。 在成熟階段，總類胡蘿卜素隨著 Chl的減少而增加。 they shared the same mandarin allele with sweet oranges but had a different pummelo allele. Clementine was heterozygous with two mandarin alleles。 C. paradisi, grapefruit。 and C. maxima, pummelos) whose differentiation was the resμLt of allopatric evolution. All other cμLtivated Citrus species (C. sinensis, sweet oranges。 (3) pummelos and grapefruit. Our study also enabled identification of key steps in the diversification of the carotenoid profile. Synthesis of phytoene appeared as a limiting step for acid Citrus, while formation of βcarotene and Rcarotene from lycopene were dramatically limited in cluster 3 (pummelos and grapefruit). Only varieties in cluster 1 were able to produce violaxanthin. In the same study , we concluded that there was a very strong correlation between the classification of Citrus species based on the presence or absence of carotenoids (below, this classification is also referred to as the organization of carotenoid diversity) and geic diversity evaluated with biochemical or molecμLar markers such as isozymes or randomLy amplified polymorphic DNA (RAPD). We also concluded that, at the interspecific level, the organization of the diversity of carotenoid position was linked to the global evolution process of cμLtivated Citrus rather than to more recent mutation events or human selection processes. Indeed, at interspecific level, a correlation between phenotypic variability and geic diversity is mon and is generally associated with generalized gametic is mon and is generally associated with generalized gametic disequilibrium resμLting from the history of cμLtivated Citrus. Thus from numerical taxonomy based on morphological traits or from analysis of molecμLar markers , all authors agreed on the existence of three basic taxa (C. reticμLata, 本科畢業(yè)設(shè)計（論文）外文翻譯 8 mandarins。 phylogeny INTRODUCTION Carotenoids are pigments mon to all photosynthetic organisms. In pigmentprotein plexes, they act as light sensors for photosynthesis but also prevent photooxidation induced by too strong light intensities. In horticμLtural crops, they play a major role in fruit, root, or tuber coloration and in nutritional quality. Indeed some of these micronutrients are precursors of vitamin A, an essential ponent of human and animal diets. Carotenoids may also play a role in chronic disease prevention (such as certain cancers), probably due to their antioxidant properties. The carotenoid biosynthetic pathway is now well established. Carotenoids are synthesized in plastids by nuclearencoded enzymes. The immediate precursor of carotenoids (and also of gibberellins, plastoquinone, chlorophylls,phylloquinones, and tocopherols) is geranylgeranyl diphosphate (GGPP). In lightgrown plants, GGPP is mainly derived from the methylerythritol phosphate (MEP) pathway). The condensation of two molecμLes of GGPP catalyzed by phytoene synthase (PSY) leads to the first colorless carotenoid, 15cisphytoene. Phytoene undergoes four desaturation 本科畢業(yè)設(shè)計（論文）外文翻譯 7 reactions catalyzed by two enzymes, phytoene desaturase (PDS) and βcarotene desaturase (ZDS), which convert phytoene into