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See detailDelayed chlorophyll accumulation and pigment photodestruction in the epicotyls of dark-grown pea (Pisum sativum)
Boddi, B.; Loudeche, R.; Franck, Fabrice ULg

in Physiologia Plantarum (2005), 125(3), 365-372

A comparison was performed of the tetrapyrrole transformations that occur upon irradiation of epicotyl or leaves of dark-grown Pisum sativum L. (var. Zsuzsi, Hungary). High performance liquid ... [more ▼]

A comparison was performed of the tetrapyrrole transformations that occur upon irradiation of epicotyl or leaves of dark-grown Pisum sativum L. (var. Zsuzsi, Hungary). High performance liquid chromatography analysis after continuous or flash-irradiation showed that the biosynthetic pathway from protochlorophyllide (Pchlide) to chlorophyll (Chl) a was markedly slowed down at the step of the reduction of geranylgeranyl(gg)-Chl to dihydrogeranylgeranyl (dhgg)-Chl in epicotyls, whereas phytyl-Chl was synthesized in leaves subjected to the same light treatments. Quantitative pigment analysis during continuous irradiations of different intensities also showed that significant Pchlide photodestruction occurred in epicotyls even under weak light. When both Pchlide and chlorophyllide and/or chlorophylls were present in epicotyls, Pchlide photodestruction was faster under 630-nm light than under 670-nm light, which indicates that this process is most efficiently promoted by Pchlide excitation. Pre-incubation of epicotyl segments with 10 mM ascorbate partly alleviated pigment photodestruction in white light. It is concluded that formation of photoactive Pchlide-Pchlide oxidoreductase complexes is important to prevent fast pigment photooxidation after Pchlide accumulation in the dark. [less ▲]

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See detailChanges in the room-temperature emission spectrum of chlorophyll during fast and slow phases of the Kautsky effect in intact leaves
Franck, Fabrice ULg; Dewez, D.; Popovic, R.

in Photochemistry & Photobiology (2005), 81(2, Mar-Apr), 431-436

Changes in the room-temperature emission spectrum of chlorophyll (Chl) were analyzed using fast diode-array recordings during the Kautsky effect in mature and in greening barley leaves. In mature leaves ... [more ▼]

Changes in the room-temperature emission spectrum of chlorophyll (Chl) were analyzed using fast diode-array recordings during the Kautsky effect in mature and in greening barley leaves. In mature leaves, the comparison of F-O (basal level of fluorescence yield at transient O) and F-M (maximum level of fluorescence yield at transient M) spectra showed that the relative amplitude of total variable fluorescence was maximal for the 684 nm Photosystem II (PSII) band and minimal for the 725 nm Photosystem I band. During the increase from F-O to F-M, a progressive redshift of the spectrum of variable fluorescence occurred. This shift reflected the different fluorescence rise kinetics of different layers of chloroplasts inside the leaf. This was verified by simulating the effect of screening on the emission spectrum of isolated chloroplasts and by experiments on greening leaves with low Chl content. In addition, experiments performed at different greening stages showed that the presence of uncoupled Chl at early-greening stages and light-harvesting complex II (LHCII) at later stages have detectable but minor effects on the shape of room-temperature emission spectra. When strong actinic light was applied to mature green leaves, the slow fluorescence yield, which declined from F-M to FT (steady-state level of fluorescence yield at transient T), was accompanied by a slight redshift of the 684 nm PSII band because of nonphotochemical quenching of short-wavelength-emitting Chl ascribed to LHCII. [less ▲]

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See detailProtochlorophyllide phototransformation in the bundle sheath cells of Zea mays
Dewez, D.; Franck, Fabrice ULg; Popovic, R. et al

in Journal of Photochemistry and Photobiology B : Biology (2004), 75(1-2), 73-80

The protochlorophyllide transformation process was investigated by using comparative analysis of 77 K fluorescence spectral changes occurring in isolated bundle sheath (BS) cells of etiolated Zea mays ... [more ▼]

The protochlorophyllide transformation process was investigated by using comparative analysis of 77 K fluorescence spectral changes occurring in isolated bundle sheath (BS) cells of etiolated Zea mays leaves after being exposed to a 200 ms saturating flash. Deconvolution analysis of the fluorescence spectra showed essential differences in the ratio of protochlorophyll(ides) and chlorophyll(ides) spectral forms indicating for BS cells to have a characteristic pathway of protochlorophyllide transformation. Bundle sheath cells showed a high ratio between non-photoactive protochlorophyll(ide)-F632 and photoactive protochlorophyllide-F655. In those cells, the 200 ins flash triggered a preferential formation of chlorophyll(ide)-F675 which remained stable in the dark for at least 90 min. Isolated BS cells showed an accumulation of chlorophyll(ide)-F675 resulting in the formation of inactive photosystem II. However for mesophyll cells of intact leaves, it was found to have a high ratio between photoactive and non-photoactive protochlorophyll(ide), showing the succession of chlorophyll(ide) forms usually known in C-3 plants. Protochlorophyllide phototransformation pathway in BS cells related to early stages of plastid differentiation triggered by light may indicate specific conditions for PSII assembly process leading to inactive PSII forms. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailPhotosynthesis and state transitions in mitochondrial mutants of Chlamydomonas reinhardtii affected in respiration
Cardol, Pierre ULg; Gloire, Geoffrey ULg; Havaux, M. et al

in Plant Physiology (2003), 133(4), 2010-2020

Photosynthetic activities were analyzed in Chlamydomonas reinhardtii mitochondrial mutants affected in different complexes (I, III, IV, I + III, and I + IV) of the respiratory chain. Oxygen evolution ... [more ▼]

Photosynthetic activities were analyzed in Chlamydomonas reinhardtii mitochondrial mutants affected in different complexes (I, III, IV, I + III, and I + IV) of the respiratory chain. Oxygen evolution curves showed a positive relationship between the apparent yield of photosynthetic linear electron transport and the number of active proton-pumping sites in mitochondria. Although no significant alterations of the quantitative relationships between major photosynthetic complexes were found in the mutants, 77 K fluorescence spectra showed a preferential excitation of photosystem I (PSI) compared with wild type, which was indicative of a shift toward state 2. This effect was correlated with high levels of phosphorylation of light-harvesting complex II polypeptides, indicating the preferential association of light-harvesting complex II with PSI. The transition to state 1 occurred in untreated wild-type cells exposed to PSI light or in 3-(3,4-dichlorophenyl)-1,1-dimethylurea-treated cells exposed to white light. In mutants of the cytochrome pathway and in double mutants, this transition was only observed in white light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. This suggests higher rates of non-photochemical plastoquinone reduction through the chlororespiratory pathway, which was confirmed by measurements of the complementary area above the fluorescence induction curve in dark-adapted cells. Photo-acoustic measurements of energy storage by PSI showed a stimulation of PSI-driven cyclic electron flow in the most affected mutants. The present results demonstrate that in C. reinhardtii mutants, permanent defects in the mitochondrial electron transport chain stabilize state 2, which favors cyclic over linear electron transport in the chloroplast. [less ▲]

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See detailProtochlorophyllide reduction: Mechanisms and evolution
Schoefs, B.; Franck, Fabrice ULg

in Photochemistry and Photobiology (2003), 78(6), 543-557

Protochlorophyllide (Pchlide) reductases are key enzymes in the process of chlorophyll biosynthesis. In this review, current knowledge on the molecular organization, substrate specificity and assembly of ... [more ▼]

Protochlorophyllide (Pchlide) reductases are key enzymes in the process of chlorophyll biosynthesis. In this review, current knowledge on the molecular organization, substrate specificity and assembly of the light-dependent reduced nicotinamide adenine dinucleotide phosphate:Pchlide oxidoreductases are discussed. Characteristics of light-independent enzymes are also described briefly, and the possible reasons for the selection of light-dependent enzymes during the course of evolution are discussed. [less ▲]

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See detailEarly reactions of light-induced protochlorophyllide and chlorophyllide transformations analyzed in vivo at room temperature with a diode array spectrofluorometer
Boddi, B.; Popovic, R.; Franck, Fabrice ULg

in Journal of Photochemistry and Photobiology B : Biology (2003), 69(1), 31-39

The steps of protochlorophyllide (Pchlide) photoreduction and subsequent chlorophyllide (Chlide) transformations which occur in the seconds to minutes time-scale were studied using a diode array ... [more ▼]

The steps of protochlorophyllide (Pchlide) photoreduction and subsequent chlorophyllide (Chlide) transformations which occur in the seconds to minutes time-scale were studied using a diode array spectrofluorometer in dark-grown barley leaves. The intensity of the excitation light was varied between 3 and 2500 mumol m(-2) s(-1) and a series of fluorescence spectra were recorded at room temperature in the seconds and minutes time scales. In certain experiments, 77-K emission spectra were measured with the same equipment. The high quality of the spectra allowed us to run spectral resolution studies which proved the occurrence, at room temperature, of multiple Pchlide and Chlide forms found previously in 77-K spectra. The comparison of the 77-K and room-temperature spectra showed that the fluorescence yields of the nonphotoactive 633-nm Pchlide form and of the Chlide product emitting at 678 nm were temperature independent. The fluorescence intensity of aggregated NADPH-pigment-POR complexes (photoactive 656-nm Pchlide and 693-nm Chlide forms) were strongly increased at 77 K, while that of the NADP(+)-Chlide-POR (684-686-nm Chlide form) was much less affected by temperature. Information was obtained also about the dynamics of the transformation of pigment forms in the light at different photon densities. At low light intensities, the phototransformation of the 642-644-nm Pchlide form was faster than that of the 654-656-nm form. The relative amplitudes of Gaussian components related to different Chlide forms found after exposure to a constant amount of photons strongly depended on the light intensity used. Strong quenching of all Chlide components occurred upon prolonged exposure to high intensity light. These effects are discussed by considering the interconversion processes between different forms of the pigment-protein complexes, their relative fluorescence yields and energy migration processes. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailResolution of the Photosystem I and Photosystem II contributions to chlorophyll fluorescence of intact leaves at room temperature
Franck, Fabrice ULg; Juneau, P.; Popovic, R.

in Biochimica & Biophysica Acta (2002), 1556(2-3), 239-246

Green leaves illuminated with photosynthetically active light emit red fluorescence, whose time-dependent intensity variations reflect photosynthetic electron transport (the Kautsky effect). Usually ... [more ▼]

Green leaves illuminated with photosynthetically active light emit red fluorescence, whose time-dependent intensity variations reflect photosynthetic electron transport (the Kautsky effect). Usually, fluorescence variations are discussed by considering only the contribution of PSII-associated chlorophyll a, although it is known that the fluorescence of PSI-associated chlorophyll a also contributes to the total fluorescence [Aust. J. Plant Physiol. 22 (1995) 13 1]. Because the fluorescence emitted by each photosystem cannot be measured separately by selecting the emission wavelength in in vivo conditions, the contribution of PSI to total fluorescence at room temperature is still in ambiguity. By using a diode array detector, we measured fluorescence emission spectra corresponding to the minimal (F-O) and maximal (F-M) fluorescence states. We showed that the different shapes of these spectra were mainly due to a higher contribution of PSI chlorophylls in the F-O spectrum. By exciting PSI preferentially, we recorded a reference PSI emission spectrum in the near far-red region. From the F-O and F-M spectra and from this PSI reference spectrum, we derived specific PSI and PSII emission spectra in both the F-O and F-M states. This enables to estimate true value of the relative variable fluorescence of PSII, which was underestimated in previous works. Accurate separation of PSI-PSII fluorescence emission spectra will also enable further investigations of the distribution of excitation energy between PSI and PSII under in vivo conditions. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailRegulation of Etioplast Pigment-Protein Complexes, Inner Membrane Architecture, and Protochlorophyllide a Chemical Heterogeneity by Light-Dependent Nadph:Protochlorophyllide Oxidoreductases a and B
Franck, Fabrice ULg; Sperling, U.; Frick, G. et al

in Plant Physiology (2000), 124(4), 1678-96

The etioplast of dark-grown angiosperms is characterized by the prolamellar body (PLB) inner membrane, the absence of chlorophyll, and the accumulation of divinyl and monovinyl derivatives of ... [more ▼]

The etioplast of dark-grown angiosperms is characterized by the prolamellar body (PLB) inner membrane, the absence of chlorophyll, and the accumulation of divinyl and monovinyl derivatives of protochlorophyll(ide) a [Pchl(ide) a]. Either of two structurally related, but differentially expressed light-dependent NADPH:Pchlide oxidoreductases (PORs), PORA and PORB, can assemble the PLB and form dark-stable ternary complexes containing enzymatically photoactive Pchlide-F655. Here we have examined in detail whether these polypeptides play redundant roles in etioplast differentiation by manipulating the total POR content and the PORA-to-PORB ratio of etiolated Arabidopsis seedlings using antisense and overexpression approaches. POR content correlates closely with PLB formation, the amounts, spectroscopic properties, and photoreduction kinetics of photoactive Pchlide, the ratio of photoactive Pchlide-F655 to non-photoactive Pchl(ide)-F632, and the ratio of divinyl- to monovinyl-Pchl(ide). This last result defines POR as the first endogenous protein factor demonstrated to influence the chemical heterogeneity of Pchl(ide) in angiosperms. It is intriguing that excitation energy transfer between different spectroscopic forms of Pchl(ide) in etiolated cotyledons remains largely independent of POR content. We therefore propose that the PLB contains a minimal structural unit with defined pigment stoichiometries, within which a small amount of non-photoactive Pchl(ide) transfers excitation energy to a large excess of photoactive Pchlide-F655. In addition, our data suggests that POR may bind not only stoichiometric amounts of photoactive Pchlide, but also substoichiometric amounts of non-photoactive Pchl(ide). We conclude that the typical characteristics of etioplasts are closely related to total POR content, but not obviously to the specific presence of PORA or PORB. [less ▲]

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See detailLocalization of Nadph-Protochlorophyllide Reductase in Plastids of Barley at Different Greening Stages
Barthelemy, X.; Bouvier, G.; Radunz, A. et al

in Photosynthesis Research (2000), 64(1), 63-76

The localization of protochorophyllide (Pchlide) and of NADPH-protochlorophyllide oxidoreductase (POR, EC 1.6.99.1) within (etio)chloroplasts has been investigated at selected stages of greening of barley ... [more ▼]

The localization of protochorophyllide (Pchlide) and of NADPH-protochlorophyllide oxidoreductase (POR, EC 1.6.99.1) within (etio)chloroplasts has been investigated at selected stages of greening of barley seedlings. Pchlide pigment and POR protein contents were evaluated in different plastid membrane fractions by fluorescence spectroscopy and immunoblot analysis using a monospecific polyclonal antibody raised against the purified enzyme. Fluorescence analysis showed the presence of Pchlide in both the envelope and thylakoid membranes. During greening, the Pchlide content, expressed on a total protein basis, decreased in thylakoid membranes, whereas it increased in the envelope membranes. POR proteins were detected mainly in thylakoid membranes at early greening stages. In contrast, the weak amount of POR proteins was associated more specifically with envelope membranes of mature chloroplasts. Whatever the greening stage, thylakoid-bound Pchlide and POR proteins were more abundant in the thylakoid regions which remained unsolubilized after mild Triton treatment used as standard procedure to prepare PS II particles. This suggests the preferential association of Pchlide and POR to the appressed regions of thylakoids. [less ▲]

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See detailSpectroscopic properties of protochlorophyllide analyzed in situ in the course of etiolation and in illuminated leaves
Schoefs, B.; Bertrand, M.; Franck, Fabrice ULg

in Photochemistry & Photobiology (2000), 72(1), 85-93

The spectroscopic properties of photoactive (ie. flash-transformable) and nonphotoactive protochlorophyll(ide)s (Pchl(ide)) were reinvestigated during the development of bean leaves in darkness. Two ... [more ▼]

The spectroscopic properties of photoactive (ie. flash-transformable) and nonphotoactive protochlorophyll(ide)s (Pchl(ide)) were reinvestigated during the development of bean leaves in darkness. Two phases in the process of Pchl(ide) accumulation were apparent from quantitative measurements of pigment content: a lag phase (first week) during which photoactive Pchl(ide) accumulated faster than nonphotoactive Pchl(ide); and a fast phase (second week), showing parallel accumulation of both types of Pchl(ide). 'Flashed-minus-dark' absorbance difference spectra recorded in situ at 77 K showed that P650-655 was the predominant form of photoactive protochlorophyllide regardless of developmental stage. Quantitative analysis of energy migration processes between the Pchl(ide) forms showed the existence of energy transfer units containing a 1:8 ratio of nonphotoactive and photoactive Pchl(ide)s during development. Gaussian deconvolution of in situ 77 K fluorescence spectra indicated that the 633 nm band of nonphotoactive Pchl(ide) was made of four bands, at 625, 631, 637 and 643 nm, whose relative amplitudes only slightly changed during development. The emission band of photoactive Pchlide was also analyzed using the same method. Three components were found at 644, 652 and 657 nm, The emission band of P650-655 included the last two components, which become predominant only in fully etiolated plants. Photoactive Pchlide with an emission maximum at 653 nm was detected in the light during development of leaves of photoperiodically grown plants. [less ▲]

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See detailAnalysis of fluorescence lifetime of protochlorophyllide and chlorophyllide in isolated etioplast membranes measured from multifrequency cross-correlation phase fluorometry
Mysliwa-Kurdziel, B.; Franck, Fabrice ULg; Strzalka, K.

in Photochemistry & Photobiology (1999), 70(4), 616-623

The fluorescence decays of protochlorophyllide (Pchlide) and of chlorophyllide (Chlide) in wheat etioplast membranes were analyzed using a multiexponential fluorescence decay model. Using different ... [more ▼]

The fluorescence decays of protochlorophyllide (Pchlide) and of chlorophyllide (Chlide) in wheat etioplast membranes were analyzed using a multiexponential fluorescence decay model. Using different excitation wavelengths from 430 to 470 nm, we found that a triple-exponential model at 14 degrees C and a double-exponential model at -170 degrees C were adequate to describe the Pchlide fluorescence decay. We discuss the origin of the three fluorescence lifetime components at 14 degrees C on the basis of the dependence of their fractional intensities on the excitation wavelength and by correlating the fractional intensities with integrated fluorescence intensities of different Pchlide forms in steady-state fluorescence spectra, The fluorescence decay of the main Pchlide form, photoactive Pchlide-F657, is shown to have a complex character with a fast component of 0.25 ns and a slower component of about 2 ns. Two lifetime components of 2 ns and 5.5-6.0 ns are ascribed to the second photoactive form, Pchlide-F645, and to nonphotoactive Pchlide forms, respectively. In etioplast membranes preilluminated by a short saturating fight pulse, we found a single 5.0 ns component for Chlide-F688 (the Chlide-NADPH :protochlorophyllide oxidoreductase [POR]-NADP(+) complex) and an additional 1.6 ns component when the formation of Chlide-F696 (the Chlide-POR-NADPH complex) was promoted by exogenous NADPH, From the fluorescence lifetime results we evaluated the quantum yield of the primary photoreaction by Chlide-F696 as being 70%. [less ▲]

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See detailProtochlorophyllide-NADP(+) and protochlorophyllide-NADPH complexes and their regeneration after flash illumination in leaves and etioplast membranes of dark-grown wheat
Franck, Fabrice ULg; Bereza, B.; Boddi, B.

in Photosynthesis Research (1999), 59(1), 53-61

The fast (1 min) regeneration process of the photoactive Pchlide forms after a light flash was studied in etiolated wheat leaves, and this process was simulated in vitro by incubating etioplast inner ... [more ▼]

The fast (1 min) regeneration process of the photoactive Pchlide forms after a light flash was studied in etiolated wheat leaves, and this process was simulated in vitro by incubating etioplast inner membranes of wheat with excess NADPH or NADP(+). The 77 K fluorescence spectra were recorded after flash illumination, dark incubation and a subsequent flash illumination of the samples. A non-photoactive Pchlide form with an emission maximum at 650 nm was transiently detected in leaves during regeneration of a photoactive Pchlide form with an emission maximum at 654 nm. Gaussian deconvolution of fluorescence spectra of isolated membranes showed that this 650 nm form appeared in conditions of excess NADP(+), as suggested in previous studies. Additionally a Pchlide form emitting at 638.5 nm was detected in the same conditions. The analysis of the spectra of leaves at different times after a flash indicated that these two non-photoactive forms are involved as intermediates in the regeneration of photoactive Pchlide. This regeneration is in correlation with the production of the Chlide form emitting at 676 nm. The results demonstrate that, in vivo, part of the NADPH:protochlorophyllide oxidoreductase is reloading with nonphotoactive Pchlide on a fast time-scale and that the 676 nm Chlide form is the released product of the phototransformation in this process. [less ▲]

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See detailChanges in endothermic transitions associated with light-induced chlorophyllide formation, as investigated by differential scanning calorimetry
Mysliwa-Kurdziel, B.; Franck, Fabrice ULg; Chahdi, M. A. O. et al

in Physiologia Plantarum (1999), 107(2), 230-239

The changes in thermal transitions associated with protochlorophyllide (Pchlide) into chlorophyllide (Chlide) phototransformation were investigated using sensitive differential scanning calorimetry (DSC ... [more ▼]

The changes in thermal transitions associated with protochlorophyllide (Pchlide) into chlorophyllide (Chlide) phototransformation were investigated using sensitive differential scanning calorimetry (DSC), Two groups of endothermic transitions, each composed of several components, were observed between 25 and 90 degrees C for prolamellar body (PLB) membranes isolated from etiolated wheat (Triticum aestivum) leaves. The first group, located in the 20-45 degrees C region, was strongly affected by a short light pulse given prior to measurement, A decrease of this group of transitions was observed shortly after illumination and it was hardly detected in PLBs measured after the Chlide Shibata shift. Calorimetric results were supported by 77-K fluorescence emission spectra measured for continuously heated samples at different temperatures. We interpreted the DSC band observed between 20 and 45 degrees C as due to the disaggregation of Pchlide- (or Chlide-)-reductase-NADPH complexes, More detailed analysis using Gaussian deconvolution showed that this band was composed of three transitions at 32, 39 and 41 degrees C. The second group of transitions was detected in the 45-80 degrees C region, the same as for mature thylakoids. Its main component at 60 degrees C was not affected significantly by a short light pulse. By comparison of thermograms obtained for PLBs with those for mature thylakoid membranes, this transition was identified as the ATPase denaturation band. [less ▲]

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See detailChlorophyll Synthesis in Dark-Grown Pine Primary Needles
Schoefs, B.; Franck, Fabrice ULg

in Plant Physiology (1998), 118(4), 1159-68

The pigment content of dark-grown primary needles of Pinus jeffreyi L. and Pinus sylvestris L. was determined by high-performance liquid chromatography. The state of protochlorophyllide a and of ... [more ▼]

The pigment content of dark-grown primary needles of Pinus jeffreyi L. and Pinus sylvestris L. was determined by high-performance liquid chromatography. The state of protochlorophyllide a and of chlorophylls during dark growth were analyzed by in situ 77 K fluorescence spectroscopy. Both measurements unambiguously demonstrated that pine primary needles are able to synthesize chlorophyll in the dark. Norflurazon strongly inhibited both carotenoid and chlorophyll synthesis. Needles of plants treated with this inhibitor had low chlorophyll content, contained only traces of xanthophylls, and accumulated carotenoid precursors. The first form of chlorophyll detected in young pine needles grown in darkness had an emission maximum at 678 nm. Chlorophyll-protein complexes with in situ spectroscopic properties similar to those of fully green needles (685, 695, and 735 nm) later accumulated in untreated plants, whereas in norflurazon-treated plants the photosystem I emission at 735 nm was completely lacking. To better characterize the light-dependent chlorophyll biosynthetic pathway in pine needles, the 77 K fluorescence properties of in situ protochlorophyllide a spectral forms were studied. Photoactive and nonphotoactive protochlorophyllide a forms with emission properties similar to those reported for dark-grown angiosperms were found, but excitation spectra were substantially red shifted. Because of their lower chlorophyll content, norflurazon-treated plants were used to study the protochlorophyllide a photoreduction process triggered by one light flash. The first stable chlorophyllide photoproduct was a chlorophyllide a form emitting at 688 nm as in angiosperms. Further chlorophyllide a shifts usually observed in angiosperms were not detected. The rapid regeneration of photoactive protochlorophyllide a from nonphotoactive protochlorophyllide after one flash was demonstrated. [less ▲]

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See detailChanges of chlorophyll(ide) fluorescence yield induced by a short light pulse as a probe to monitor the early steps of etioplast phototransformation in dark-grown leaves
Eullaffroy, P.; Popovic, R.; Franck, Fabrice ULg

in Photochemistry & Photobiology (1998), 67(6), 676-682

The fluorescence yield of chlorophyll(ide) (ChI[ide]) excited by weak modulated light was recorded at room temperature during a 2 h period after a short actinic light pulse that transformed all ... [more ▼]

The fluorescence yield of chlorophyll(ide) (ChI[ide]) excited by weak modulated light was recorded at room temperature during a 2 h period after a short actinic light pulse that transformed all photoactive protochlorophyllide in dark-grown barley leaves. A typical pattern of fluorescence yield variations was found whatever the age of the leaf but with age-dependent changes in rates. Its successive phases were related to the Chl(ide) spectral shifts observed in low-temperature emission spectra. The fluorescence yield started at a high level and strongly declined during the formation of Chlide(695) from Chlide(688) within a few seconds. It increased to a transient maximum during the Shibata shift (15-25 min) that resulted in ChI(ide)(682). A final, slow decrease to a steady state occurred during the final red shift to ChI(685). Pretreatments with delta-aminolevulinic acid, chloramphenicol or 1,10-phenanthroline resulted in correlated modifications of Chl(ide) fluorescence yield transients and shifts of the low-temperature Chl(ide) emission band. The complex response of the final decrease phase of the fluorescence yield to these compounds suggests that it results both from the assembly of photosynthetic Chi proteins and from the reorganization of the etioplast membrane system. From these results it is concluded that continuous recordings of CN(ide) fluorescence yield after a short light pulse represent a useful tool to monitor the kinetics of pigment-protein organization and primary thylakoid assembly triggered by Pchlide photoreduction. [less ▲]

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See detailEtioplast differentiation in Arabidopsis: Both PORA and PORB restore the prolamellar body and photoactive protochlorophyllide-F655 to the cop1 photomorphogenic mutant
Sperling, U.; Franck, Fabrice ULg; van Cleve, B. et al

in Plant Cell (1998), 10(2), 283-296

The etioplast plastid type of dark-grown angiosperms is defined by the accumulation of the chlorophyll (Chi) precursor protochlorophyllide (Pchlide) and the presence of the paracrystalline prolamellar ... [more ▼]

The etioplast plastid type of dark-grown angiosperms is defined by the accumulation of the chlorophyll (Chi) precursor protochlorophyllide (Pchlide) and the presence of the paracrystalline prolamellar body (PLB) membrane. Both features correlate with the presence of NADFH:Pchlide oxidoreductase (FOR), a light-dependent enzyme that reduces photoactive Pchlide-F655 to chlorophyllide and plays a key role in chloroplast differentiation during greening. Two differentially expressed and regulated FOR enzymes, FORA and FORB, have recently been discovered in angiosperms. To investigate the hypothesis that etioplast differentiation requires FORA, we have constitutively overexpressed PORA and FORB in the Arabidopsis wild type and in the constitutive photomorphogenic cop1-18 (previously det340) mutant, which is deficient in the PLB and Pchlide-F655. In both genetic backgrounds, FOR overexpression increased PLB size, the ratio of Pchlide-F655 to nonphotoactive Pchl[ide]-F632, and the amount of Pchlide-F655. Dramatically, restoration of either FORA or FORB to the cop1 mutant led to the formation of etioplasts containing an extensive PLB and large amounts of photoactive Pchlide-F655. [less ▲]

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