PubMed Health⌕ Search

Biomedical subjects

C A Rebeiz

Publications and source records attributed to C A Rebeiz.

At least 37 records · Page 2Linked to original sources
PubMed1985

Chloroplast Biogenesis 49 : Differences among Angiosperms in the Biosynthesis and Accumulation of Monovinyl and Divinyl Protochlorophyllide during Photoperiodic Greening.

Various angiosperms differed in their monovinyl and divinyl protochlorophyllide biosynthetic capabilities during the dark and light phases of photoperiodic growth. Some plant species such as Cucumis sativus L., Brassica juncea (L.) Coss., Brassica kaber (DC.) Wheeler, and Portulaca oleracea L. accumulated mainly divinyl protochlorophyllide at night. Monocotyledonous species such as Avena sativa L., Hordeum vulgare L., Triticum secale L., Zea mays L., and some dicotyledonous species such as Phaseolus vulgaris L., Glycine max (L.) Merr., Chenopodium album L., and Lycopersicon esculentum L. accumulated mainly monovinyl protochlorophyllide at night.Under low light intensities meant to simulate the first 60 to 80 minutes following daybreak divinyl protochlorophyllide appeared to contribute much more to chlorophyll formation than monovinyl protochlorophyllide in species such as Cucumis sativus L. Under the same light conditions, species which accumulated mainly monovinyl protochlorophyllide at night appeared to form chlorophyll preferably via monovinyl protochlorophyllide.THESE RESULTS WERE INTERPRETED IN TERMS OF: (a) a differential contribution of monovinyl and divinyl protochlorophyllide to chlorophyll formation at daybreak in various plant species; and (b) a differential regulation of the monovinyl and divinyl protochlorophyllide biosynthetic routes by light and darkness.

Journal Article↗
PubMed1985

Chloroplast biogenesis 51 : modulation of monovinyl and divinyl protochlorophyllide biosynthesis by light and darkness in vitro.

It is shown that the monovinyl and divinyl protochlorophyllide biosynthetic patterns of etiolated maize (Zea mays L.), and cucumber (Cucumis sativus L.) seedlings and of their isolated etiochloroplasts can be modulated by light and darkness as was shown for green photoperiodically grown plants (E. E. Carey, C. A. Rebeiz 1985 Plant Physiol. 79: 1-6). In etiolated corn and cucumber seedlings and isolated etiochloroplasts poised in the divinyl protochlorophyllide biosynthetic mode by a 2 hour light pretreatment, darkness induced predominantly the biosynthesis of monovinyl protochlorophyllide in maize and of divinyl protochlorophyllide in cucumber. When etiolated seedlings and their isolated etiochloroplasts were poised in the monovinyl protochlorophyllide biosynthetic mode by a prolonged dark-pretreatment, light induced mainly the biosynthesis of divinyl protochlorophyllide in both maize and cucumber.

Journal Article↗
PubMed1983

Chlorophyll a biosynthetic routes and chlorophyll a chemical heterogeneity in plants.

A six-branched chlorophyll a biosynthetic pathway instead of a four-branched pathway has been proposed as being responsible for the formation of chlorophyll a in green plants. The several biosynthetic routes that make up the pathway have been described as leading to the formation of ten chemically different groups of chlorophyll a species. The latter differ from one another by one or more of the following modifications: (a) by having a vinyl or ethyl group at position 4 of the macrocycle, (b) by the nature of the long-chain fatty alcohols at position 7 of the macrocycle, and (c) by having a 6-membered lactone ring instead of a 5-membered cyclopentanone ring. The chemical structure of several of the metabolic intermediates of that pathway and of some of the chlorophyll a species have now been determined by primary chemical derivatization methods coupled to spectrofluorometric, nuclear magnetic resonance and mass spectral analyses. The formation of highly organized photosynthetic membranes in which some of the chlorophyll alpha molecules are specifically oriented is ascribed to the multiplicity of chlorophyll biosynthetic routes which result in the formation of multiple chlorophyll alpha chemical species. Proper orientation of chlorophyll in the photosynthetic membranes is visualized as being controlled by peripheral group modifications that either modulate the polarity of the Chl chromophore or control the magnitude of the net positive charge on the central Mg atom. Finally it is proposed that in addition to the proper orientation of chlorophyll a, chemical heterogeneity of the chlorophyll chromophores in the photosynthetic reaction centers is mandatory for efficient charge separation, and proper vectorial electron transfer.

Chlorophyll↗
PubMed1982

Chloroplast biogenesis. Identification of chlorophyllide a (E458f674) as a divinyl chlorophyllide a.

The chemical identification of chlorophyllide (E458F674) (Belanger, F. C., and Rebeiz, C. A. (1980) Plant Sci. Lett. 18, 343-350) has been confirmed by chemical derivatization coupled to spectrofluorometric, spectrophotometric, and chromatographic analysis. Chlorophyllide (E458F674) and its demetallated analog were converted by catalytic hydrogenation into mesochlorophyllide a and mesopheophorbide a. Furthermore, methyl chlorophyllide (E458F674) was converted by partial hydrogenation into a mixture of monovinyl chlorophyllide a isomers and the latter into mesochlorophyllide a by further hydrogenation. On the other hand, chemical oxidation of methyl chlorophyllide (E458F674) converted it into methyl divinyl protochlorophyllide. Chlorophyllide (E458F674) was detected in several plant species and is proposed to be an important intermediate of the chlorophyll a biosynthetic pathway.

Chemical Phenomena↗
PubMed1982

Chloroplast biogenesis. Detection of monovinyl magnesium-protoporphyrin monoester and other monovinyl magnesium-porphyrins in higher plants.

It is shown that the magnesium-protoporphyrin-6-ester pool of plants is made up of monovinyl and divinyl components which were separated by chromatography on thin layers of polyethylene. At 77K, in ether, monovinyl-Mg-protoporphyrin-6-ester exhibited fluorescence emission and excitation maxima at 589 and 417 nm, respectively. The divinyl-Mg-protoporphyrin-6-ester component exhibited red-shifted emission and excitation maxima at 591 and 424 nm respectively. Demetallation of the monovinyl and divinyl Mg-protoporphyrin ester components converted them into monovinyl and divinyl-protoporphyrin IX free bases. Catalytic Mg-mesoporphyrin ester and the demetallated free bases into mesoporphyrin ester, Monovinyl-Mg-porphyrin chemical species were also detected in the Mg-protoporphyrin IX and the Mg-protoporphyrin IX diester pools of plants. It is proposed that the Mg-protoporphyrin IX, Mg-protoporphyrin IX-6-ester, and Mg-protoporphyrin IX-diester pools of plants are heterogenous and are made up of monovinyl and divinyl chemical species.

Chloroplasts↗
PubMed1982

Chloroplast biogenesis: biosynthesis of protochlorophyll(ide) via acidic and fully esterified biosynthetic branches in higher plants.

The operation of two parallel biosynthetic pathways during the biosynthesis of the protochlorophyll(ide) pool of cucumber cotyledons was probed with the use of several [14C]tetrapyrroles in vitro. A comparison of the ratio (R) of delta-amino[14C]levulinic acid incorporation into protochlorophyllide/14C incorporation into protochlorophyllide ester with other incorporation ratios, RX, where X represents any of several [14C]tetrapyrrole substrates, allowed us to determine which exogenous 14C-labeled substrate was common precursor of protochlorophyllide and protochlorophyllide ester and which one was not. From such comparisons, a biosynthetic pathway of protochlorophyll(ide) biosynthesis is inferred. According to this pathway, protochlorophyllide is formed via an acidic (mono/dicarboxylic) biosynthetic branch, while protochlorophyllide ester is formed via a fully esterified (neutral) biosynthetic branch. The two biosynthetic branches are linked together by porphyrin ester synthetases at the level of protochlorophyllides and possibly at the level of the photoporphyrin IX and the magnesium protoporphyrin monoester pools.

Chlorophyllides↗
PubMed1981

Chloroplast biogenesis: detection of a magnesium protoporphyrin diester pool in plants.

The discovery of a novel metalloporphyrin pool in etiolated cucumber cotyledons and in dark-grown Euglena gracilis is described. The novel pool exhibited the chromatographic properties of a fully esterified metalloporphyrin, devoid of free carboxylic groups, and the spectrophotometric and spectrofluorometric properties of a magnesium protoporphyrin. Demetalation and hydrolysis indicated that the tetrapyrrole moiety of the metalloporphyrin was a protoporphyrin diester. High-pressure liquid chromatography of the fully esterified metalloporphyrin pool and gas chromatographic/mass spectroscopic analysis of the saponified alcohol fraction revealed that the latter was made up of three major long-chain alcohols. None of those alcohols was identifiable, however, with known isoprenoids such as geraniol, farnesol, or phytol. Similar analysis of the saponified alcohol fraction of the protochlorophyllide ester pool likewise revealed the presence of three major long-chain alcohols none of which was identifiable with known isoprenoid alcohols or with the alcohols of the novel metalloporphyrin pool. On the basis of the above observations, the novel metalloporphyrin pool was tentatively identified as a magnesium protoporphyrin diester pool. It is suggested that this pool is a metabolic intermediate of the fully esterified branch of the chlorophyll biosynthetic pathway [Rebeiz, C. A., Smith, B. B., Matthesis, I. R., Cohen, C. E., & McCarthy, S. A. (1978) in Chloroplast Development (Akoyunoglou, G., & Argyroudi-Akoyunoglou, J. H., Eds.) pp 56-76, Elsevier/North-Holland Bio-Medical Press, Amsterdam] and is probably the precursor of the protochlorophyllide ester pool in plants.

Chloroplasts↗
PubMed1981

Chloroplast Biogenesis 34: SPECTROFLUOROMETRIC CHARACTERIZATION IN SITU OF THE PROTOCHLOROPHYLL SPECIES IN ETIOLATED TISSUES OF HIGHER PLANTS.

The fluorescence emission and excitation properties of protochlorophyll in etiolated cucumber (Cucumis sativus L.) cotyledons and primary bean (var. Red Kidney) leaves were characterized at 77 K. Contrary to previous studies, it appears that the short-wavelength protochlorophyll emission band consists of four fluorescent components, instead of only one nonphototransformable protochlorophyll. It was demonstrated that etiolated cucumber cotyledons synthesize and accumulate nontransformable protochlorophyll (E(440), F(630)) as well as short-wavelength phototransformable protochlorophyll (E(433), F(633)), (E(444), F(636)), and (E(445), F(640)). Long-wavelength phototransformable protochlorophyll (E(450), F(657)) is also formed. In this context, E refers to the Soret excitation maxima and F refers to the red emission maxima of the protochlorophylls.IN ETIOLATED BEAN LEAVES, THE CORRESPONDING SPECIES WERE: nontransformable protochlorophyll (E(440), F(630)), short-wavelength phototransformable protochlorophylls (E(441), F(633)), (E(442), F(636)), and (E(443), F(640)), and long-wavelength phototransformable protochlorophyll (E(447), F(657)).

Journal Article↗
PubMed1980

Chloroplasts biogenesis: detection of divinylprotochlorophyllide ester in higher plants.

It is shown that the protochlorophyllide ester pool of etiolated higher plants is a faithful copy of the protochlorophyllide pool. It is made up of both monovinyl- and divinylprotochlorophyllide esters. Although the two tetrapyrroles exhibited similar emission maxima, they were distinguishable by their Soret excitation maxima, which were found at 436-437 and 443-444 nm, respectively, in ether at 77K. The two pigments were partially separated on thin layers of polyethylene. They were accompanied by two unknown fluorescent compounds. It was also shown that during greening, the protochlorophyllide ester pool maintained a constant qualitative composition. This was in sharp contrast with the drastic qualitative changes undergone by the protochlorophyllide pool of etiolated tissues grown under identical conditions.

Chlorophyll↗
PubMed1980

Chloroplast biogenesis. XXIX. The occurrence of several novel chlorophyll a and b chromophores in higher plants.

With the use of low temperature spectrofluorometry and matrix calculations it was demonstrated that the chlorophyll a pool of higher plants is made up of four different chlorophyll a chromophores. The latter were segregated by high pressure liquid chromatography on a silica column. They were designated Chl a (E432 F664), Chl a (E436 F670), Chl a (E443 F672) and Chl a (E446 F674), where E refers to the Soret excitation maximum and F to the fluorescence emission maximum at 77 K in ether. Likewise the Chl b pool was shown to consist of at least four different Chl b chromophores which were designated: Chl b (E465), Chl b (E470), Chl b (E475) and Chl b (E485). It was proposed that the various chlorophyll chromophores differed by the degree of oxidation of their side chains at the 2 and 4 positions of the macrocycle. It was also suggested that the chemical modifications at the 2 and 4 positions of the macrocycle may play an important role in positioning the different chlorophyll chromophores in the thylakoid membranes.

Chlorophyll↗
PubMed1980

Chloroplast biogenesis. Detection of divinyl protochlorophyllide in higher plants.

It is shown that the protochlorophyllide pool of etiolated higher plants is made up of both monovinyl and divinyl protochlorophyllide. Although the two pigments exhibited similar emission maxima, they were distinguishable by their Soret excitation maxima, which were found at 436 to 437 and 443 to 444 nm, respectively, in ether at 77 K. The two pigments were partially separated on thin layers of polyethylene. They were shown to be accompanied by two unknown fluorescent compounds. The latter were designated compound (E451 F626) and compound (E453 F640) where E refers to the Soret excitation maxima and F to the fluorescence emission maxima of the two unknown compounds. Furthermore, it was shown under several different growth conditions that divinyl protochlorophyllide constituted the major component of the protochlorophyllide pool.

Chlorophyll↗
PubMed1980

Chloroplast Biogenesis 31: DETECTION OF AN INHIBITOR OF PROTOCHLOROPHYLL BIOSYNTHESIS IN CUCUMBER COTYLEDONS.

An extract from cucumber cotyledons was shown to cause an inhibition of protochlorophyll biosynthesis and accumulation. The extract inhibited the net synthesis of protochlorophyll as well as the incorporation of delta-amino[(14)C]levulinic acid into protochlorophyllide and protochlorophyllide ester by excised cotyledons. The inhibition of delta-amino[(14)C]levulinic acid incorporation into the two protochlorophyll species was also observed in isolated etiochloroplasts before and after lysis of the plastids. The inhibition did not appear to involve the oxidation of the delta-aminolevulinic substrate or its translocation across the plastid membrane. Kinetic analysis of the rate of protochlorophyllide and protochlorophyllide ester biosynthesis in the presence and absence of the inhibitor suggested that the mode of inhibition of the two protochlorophyll species was different.

Journal Article↗
PubMed1979

Chloroplast Biogenesis: XXIV. Intrachloroplastic Localization of the Biosynthesis and Accumulation of Protoporphyrin IX, Magnesium-Protoporphyrin Monoester, and Longer Wavelength Metalloporphyrins during Greening.

The intraplastidic localization of the endogenous metabolic pools from protoporphyrin to protochlorophyll was determined in Cucumis sativus. The endogenous protoporphyrin, Mg-protoporphyrin monoester + longer wavelength metalloporphyrins, protochlorophyllide and protochlorophyllide ester were membrane-bound. Protoporphyrin was synthesized in the stroma and subsequently became associated with the membranes. The membrane-associated protoporphyrin was then converted into Mg-protoporphyrin monoester + longer wavelength metalloporphyrins by membrane-bound enzymes. Although lysed plastids were capable of converting exogenous delta-aminolevulinic acid to protochlorophyllide, the net synthesis of protochlorophyllide from exogenous delta-aminolevulinic acid was lost upon segregating the lysed plastids into stromal and membrane fractions and then recombining the stromal and membrane fraction prior to incubation. The segregated membrane fraction was still capable of converting protoporphyrin into Mg-protoporphyrin monoester + longer wavelength metalloporphyrins in the presence or absence of the stromal fraction. These results indicated that although the reactions from protoporphyrin to Mg-protoporphyrin monoester and longer wavelength metalloporphyrins could survive a considerable degree of plastid disruption, the reactions from Mg-protoporphyrin monoester and longer wavelength metalloporphyrins to protochlorophyllide were more sensitive to structural disorganization.

Journal Article↗
PubMed1978

Chloroplast culture: the chlorophyll repair potential of mature chloroplasts incubated in a simple medium.

The chlorophyll repair potential of mature Cucumis chloroplasts incubated in a simple Tris-HCl/sucrose medium is described. The chloroplasts were isolated from green, fully expanded Cucumis cotyledons which were capable of chlorophyll repair. This was evidenced by a functional chlorophyll biosynthetic pathway in the mature tissue. The biosynthesis of protocholorphyllide from exogenous delta-aminolevulinic acid was used as a marker for the operation of the chlorophyll biosynthetic chain between delta-aminolevulinic acid and protochlorophyllide. The conversion of exogenous protochlorophyllide into chlorophyll a was used as a marker for the operation of the chlorophyll pathway beyond protochlorophyllide. It appeared from these studies that contrary to published reports, unfortified fully developed Cucumis chloroplasts incubated in Tris-HCl/sucrose without the addition of cofactors exhibited a partial and limited chlorophyll repair capability. Their net tetrapyrrole biosynthetic competence from delta-aminolevulinic acid was confined to the accumulation of coproporphyrin. No net tetrapyrrole biosynthesis beyond coproporphyrin was observed. However, the plastids were capable of incorporating small amounts of delta-amino[4-(14)C]levulinic acid into [14C]protochlorophyllide but were incapable of converting exogenous protochlorophyllide into chlorophyll. After prolonged incubation of the unfortified chloroplasts in the dark, a fluorescent protochlorophyllide-like compound accumulated. This compound [Cp (E430-F631) was shown to be neither protochlorophyllide nor zinc-prototochlorophyllide but and a fluorescence emission maximum at 631 nm (F631) in methanol/acetone (4 : 1, v/v). Cp(E430-F631) WAS SHOWN TO BE NEITHER PROTOCHLOROPHYLLIDE NOR ZINC-PROTOTOCHLOROPHYLLIDE BUT an enzymatic degradation product of chlorophyll. The exact chemical identity of this compound has not yet been determined.

Cells, Cultured↗