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At least 19 recordsLinked to original sources
PubMed1996

Conversion of chlorophyll b to chlorophyll a via 7-hydroxymethyl chlorophyll.

Chlorophyll b is synthesized from chlorophyll a by the oxidation of the methyl group on the ring B of the tetrapyrrole ring to the formyl group. Previously, we reported that chlorophyllide b could be converted to chlorophyll a in isolated cucumber etioplasts indicating the conversion of chlorophyll b to chlorophyll a. To identify the intermediate molecule, we used barley etioplasts instead of cucumber. Chlorophyll a and an additional pigment were found after incubation of chlorophyllide b with isolated barley etioplasts. The pigment has the same retention time and absorption spectrum as 7-hydroxymethyl chlorophyll, which has the hydroxymethyl group on ring B instead of the formyl group of chlorophyll b. Authentic 7-hydroxymethyl chlorophyll was prepared by reduction of chlorophyll b by NaBH4. Chlorophyll a accumulated during the incubation of 7-hydroxymethyl chlorophyllide with etioplasts. These findings indicate that chlorophyll b is converted to chlorophyll a via 7-hydroxymethyl chlorophyll. Chlorophyll b and 7-hydroxymethyl chlorophyll accumulated within a short period of incubation of chlorophyllide b with etioplasts. However, chlorophyll a accumulated with a concomitant decrease of chlorophyll b and 7-hydroxymethyl chlorophyll. These observations also suggest that chlorophyll b is converted to 7-hydroxymethyl chlorophyll and then to chlorophyll a. Both steps required ATP.

Carbon Radioisotopes↗
PubMed1997

Conversion of Chlorophyll b to Chlorophyll a and the Assembly of Chlorophyll with Apoproteins by Isolated Chloroplasts.

The photosynthetic apparatus is reorganized during acclimation to various light environments. During adaptation of plants grown under a low-light to high-light environment, the light-harvesting chlorophyll a/b-protein complexes decompose concomitantly with an increase in the core complex of photosystem II. To study the mechanisms for reorganization of photosystems, the assembly of chlorophyll with apoproteins was investigated using isolated chloroplasts. When [14C]chlorophyllide b was incubated with chloroplasts in the presence of phytyl pyrophosphate, it was esterified and some of the [14C]chlorophyll b was converted to [14C]chlorophyll a via 7-hydroxymethyl chlorophyll. [14C]Chlorophyll a and b were incorporated into chlorophyll-protein complexes. Light-harvesting chlorophyll a/b-protein complexes of PSII had a lower [14C]chlorophyll a to [14C]chlorophyll b ratio than P700-chlorophyll a-protein complexes, indicating the specific binding of chlorophyll to apoproteins in our systems. 7-Hydroxymethyl chlorophyll, an intermediate molecule from chlorophyll b to chlorophyll a, did not become assembled with any apoproteins. These results indicate that chlorophyll b is released from light-harvesting chlorophyll a/b-protein complexes of photosystem II and converted to chlorophyll a via 7-hydroxymethyl chlorophyll in the lipid bilayer and is then used for the formation of core complexes of photosystems. These mechanisms provide the fast, fine regulation of the photosynthetic apparatus during construction of photosystems.

Journal Article↗
PubMed1988

Light-Dependent Accumulation of Radiolabeled Plastid-Encoded Chlorophyll a-Apoproteins Requires Chlorophyll a: I. Analysis of Chlorophyll-Deficient Mutants and Phytochrome Involvement.

The accumulation of radiolabeled plastid-encoded chlorophyll a-apoproteins is light dependent and is controlled at a posttranscriptional level. Illumination of dark-grown barley (Hordeum vulgare L.) with a brief pulse of red light induced the accumulation of radiolabeled chlorophyll a-apoproteins in subsequent protein synthesis assays. The induction of radiolabeled chlorophyll a-apoprotein accumulation was not affected by pretreatment of leaves with cycloheximide. Fluence response studies showed that a red light photoreceptor controls the accumulation of radiolabeled chlorophyll a-apoproteins with a threshold fluence of approximately 50 to 100 microeinsteins per square meter. While red light initiated chlorophyll a-apoprotein accumulation, this process was not reversed by a far red light treatment given immediately after the pulse of red light. The light pulse which initiated the accumulation of radiolabeled chlorophyll a-apoproteins also induced the rapid conversion of protochlorophyllide to chlorophyll a. A chlorophyll-deficient mutant, xan-f(10), which is blocked in chlorophyll biosynthesis prior to protochlorophyllide formation, failed to accumulate radiolabeled chlorophyll a-apoproteins in the light even though transcripts for these apoproteins were present. A second mutant, xan-j(64), which accumulates chlorophyllide in the light but only low levels of chlorophyll a, also showed reduced accumulation of radiolabeled chlorophyll a-apoproteins upon illumination. These results suggest that the light-induced conversion of protochlorophyllide to chlorophyll a is necessary for accumulation of the plastid-encoded chlorophyll a-apoproteins and one red light photoreceptor controlling this response is the protochlorophyllide holochrome.

Journal Article↗
PubMed2001

Effects of chlorophyll a, chlorophyll b, and xanthophylls on the in vitro assembly kinetics of the major light-harvesting chlorophyll a/b complex, LHCIIb.

The major light-harvesting chlorophyll a/b complex (LHCIIb) of photosystem II in higher plants can be reconstituted with pigments in lipid-detergent micelles. The pigment-protein complexes formed are functional in that they perform efficient internal energy transfer from chlorophyll b to chlorophyll a. LHCIIb formation in vitro, can be monitored by the appearance of energy transfer from chlorophyll b to chlorophyll a in time-resolved fluorescence measurements. LHCIIb is found to form in two apparent kinetic steps with time constants of about 30 and 200 seconds. Here we report on the dependence of the LHCIIb formation kinetics on the composition of the pigment mixture used in the reconstitution. Both kinetic steps slow down when the concentration of either chlorophylls or carotenoids is reduced. This suggests that the slower 200 seconds formation of functional LHCIIb still includes binding of both chlorophylls and carotenoids. LHCIIb formation is accelerated when the chlorophylls in the reconstitution mixture consist predominantly of chlorophyll a although the complexes formed are thermally less stable than those reconstituted with a chlorophyll a:b ratio < or = 1. This indicates that although chlorophyll a binding is more dominant in the observed rate of LHCIIb formation, the occupation of (some) chlorophyll binding sites with chlorophyll b is essential for complex stability. The accelerating effect of various carotenoids (lutein, zeaxanthin, violaxanthin, neoxanthin) on LHCIIb formation correlates with their affinity to two lutein-specific binding sites. We conclude that the occupation of these two carotenoid binding sites but not of the third (neoxanthin-specific) binding site is an essential step in the assembly of LHCIIb in vitro.

Binding Sites↗
PubMed1983

Aggregation of chlorophylls in monolayers. V. The effect of water on chlorophyll a and chlorophyll b in mono and multilayer arrays.

The nature of the interactions between water molecules and monolayers and multilayers of chlorophyll a (Chl a), and monolayers and multilayers of Chl b. obtained by the Langmuir-Blodgett technique, is examined by infrared spectroscopy. Following deposition of the monolayer or multilayer of Chl a or Chl b onto a plate, repetitive scans showed some modifications in the infrared spectra which are interpreted as a reorganization of the molecules as some water molecules leave the array. Drying the sample further modifies the spectra, which indicates the departure of more tenacious water molecules. Putting the sample in a moist atmosphere does not restore the original spectrum. This is an indication of a nonreversibie reorganization in the chlorophyll array. The spectra of the monolayer of chlorophyll are much more complicated than those of the multilayer, owing to the nonintegrating effect of the monolayer, which reveals the perturbing effect of the different dielectric milieux on each functional group. On the basis of the analysis of the spectra and the information gathered from the surface pressure isotherms, a model is proposed for the monolayer arrangement at the air/water interface which implies two set of dimers of water per molecule of chlorophyll. One pair of dimers constitutes the water of the first kind and is composed of vapor-like dimers. This kind of water is situated between the porphyrin planes of chlorophyll molecules and is easily removed from the monolayer. The second pair of dimers is composed of water of the second and third kinds situated between the Mg atom of the chlorophyll molecules and the water of the subphase. The second kind of water is closest to the Mg atom and is the most difficult one to remove. The third kind of water is closest to the surface and its mobility is intermediate between that of water of the first kind and that of water of the second kind. Comparing the infrared spectra of a freshly prepared monolayers of Chl a with the resonance Raman spectra of intact chloroplasts (M. Lutz, Biochim. Biophys. Acta 460 (1977) 408), we notice great similarities. This is an indication that the model we propose for the monolayer of Chl a could play an important role in the chloroplast.

Journal Article↗
PubMed1977

Chlorophyll lasers: Stimulated light emission by chlorophylls and Mg-free chlorophyll derivatives.

Stimulated emission and lasing have been demonstrated for chlorophyll a, chlorophyll b, and bacteriochlorophyll a as well as for the Mg-free chlorophyll derivatives pheophytin a and methyl pheophorbide a. Population inversion was obtained by optically pumping with an N(2) laser. For the three chlorophylls, lasing was observed for only the (0,0) vibronic region of the S(1) --> S(0) fluorescence band. In contrast, lasing was observed for both the (0,0) and (0,1) vibronic regions of the S(1) --> S(0) fluorescence band of pheophytin a and methyl pheophorbide a. Differences between the lasing behavior of the chlorophylls and the Mg-free derivatives probably reflect differences in aggregation behavior. Laser pulses of duration shorter than the fluorescence lifetimes were generated. This result suggests that stimulated emission must be considered in the interpretation of fluorescence lifetime data for in vitro and in vivo chlorophyll-containing systems.

Journal Article↗
PubMed1998

Chlorophyll a oxygenase (CAO) is involved in chlorophyll b formation from chlorophyll a.

Chlorophyll b is an ubiquitous accessory pigment in land plants, green algae, and prochlorophytes. Its biosynthesis plays a key role in the adaptation to various light environments. We isolated six chlorophyll b-less mutants by insertional mutagenesis by using the nitrate reductase or argininosuccinate lyase genes as tags and examined the rearrangement of mutant genomes. We found that an overlapping region of a nuclear genome was deleted in all mutants and that this encodes a protein whose sequence is similar to those of methyl monooxygenases. This coding sequence also contains putative binding domains for a [2Fe-2S] Rieske center and for a mononuclear iron. The results demonstrate that a chlorophyll a oxygenase is involved in chlorophyll b formation. The reaction mechanism of chlorophyll b formation is discussed.

Amino Acid Sequence↗
PubMed1994

Ultrafast chlorophyll b-chlorophyll a excitation energy transfer in the isolated light harvesting complex, LHC II, of green plants. Implications for the organisation of chlorophylls.

The excitation energy transfer between chlorophyll b (Chl b) and chlorophyll a (Chl a) in the isolated trimeric chlorophyll-a/b-binding protein complex of spinach photosystem 2 (LHC II) has been studied by femtosecond spectroscopy. In the main absorption band of Chl b the ground state recovery consists of two components of 0.5 ps and 2.0 ps, respectively. Also in the Chl a absorption band, at 665 nm, the ground state recovery is essentially bi-exponential. In this case is, however, the fastest relaxation lifetime is a 2.0 ps component followed by a slower component with a lifetime in the order of 10-20 ps. In the Chl b absorption band a more or less constant anisotropy of r = 0.2 was observed during the 3 ps the system was monitored. In the Chl a absorption band there was, however, a relaxation of the anisotropy from r = 0.3 to a quasi steady state level of r = 0.18 in about 1 ps. Since the 0.5 ps component is only seen upon selective excitation of Chl b we assign this component to the energy transfer between Chl b and Chl a. The other components most likely represents redistribution processes of energy among spectrally different forms of Chl a. The energy transfer process between Chl b and Chl a can well be explained by the Förster mechanism which also gives a calculated distance of 13 A between interacting chromophores. The organisation of chlorophylls in LHC II is discussed in view of the recent crystal structure data (1991) Nature 350, 130].

Chlorophyll↗
PubMed1985

Aggregation of chlorophylls in monolayers. VI. Infrared study of the CH stretching bands of chlorophyll a and of chlorophyll b in monolayers.

The CH vibrational stretch bands of chlorophyll (Chl) in monolayers, obtained by the Langmuir-Blodgett technique have been studied by infrared spectroscopy. Compared to a solution or to a multilayer which shows three to four bands, the spectra of Chl a or Chl b molecules in monolayers have revealed more than seven bands, which are assigned to the various CH groups in the molecule. In contrast to solutions or to multilayer samples which give featureless bands, each band of the monolayers is composed of many components which are modified when the system is perturbed either by drying or by hydration techniques. The separation between the components of the CH aliphatic bands is typical of crystalline field splitting and the modification of the intensities of these components is associated with the movement of the phytyl chain of the chlorophyll molecules. The CH aromatic stretch bands have been observed; the displacement and variation of the intensities of these bands are associated with deformation of the porphyrin ring. The CH band of the formyl group on Chl b has also been observed. The displacement and variation of the intensity of this band are related to the association that this group makes with the surrounding molecules and with the displacement of the porphyrin ring.

Journal Article↗
PubMed1999

Chlorophyll b to chlorophyll a conversion precedes chlorophyll degradation in Hordeum vulgare L.

This study reveals by in vivo deuterium labeling that in higher plants chlorophyll (Chl) b is converted to Chl a before degradation. For this purpose, de-greening of excised green primary leaves of barley (Hordeum vulgare) was induced by permanent darkness in the presence of heavy water (80 atom % (2)H). The resulting Chl a catabolite in the plant extract was subjected to chemical degradation by chromic acid. 3-(2-Hydroxyethyl)-4-methyl-maleimide, the key fragment that originates from the Chl catabolite, was isolated. High resolution (1)H-, (2)H-NMR and mass spectroscopy unequivocally demonstrates that a fraction of this maleimide fragment consists of a mono-deuterated methyl group. These results suggest that Chl b is converted into Chl a before degradation. Quantification proves that the initial ratio of Chl a:Chl b in the green plant is preserved to about 60-70% in the catabolite composition isolated from yellowing leaves. The incorporation of only one deuterium atom indicates the involvement of two distinguishable redox enzymes during the conversion.

Chlorophyll↗
PubMed2005

Chlorophyll breakdown in senescent Arabidopsis leaves. Characterization of chlorophyll catabolites and of chlorophyll catabolic enzymes involved in the degreening reaction.

During senescence, chlorophyll (chl) is metabolized to colorless nonfluorescent chl catabolites (NCCs). A central reaction of the breakdown pathway is the ring cleavage of pheophorbide (pheide) a to a primary fluorescent chl catabolite. Two enzymes catalyze this reaction, pheide a oxygenase (PAO) and red chl catabolite reductase. Five NCCs and three fluorescent chl catabolites (FCCs) accumulated during dark-induced chl breakdown in Arabidopsis (Arabidopsis thaliana). Three of these NCCs and one FCC (primary fluorescent chl catabolite-1) were identical to known catabolites from canola (Brassica napus). The presence in Arabidopsis of two modified FCCs supports the hypothesis that modifications, as present in NCCs, occur at the level of FCC. Chl degradation in Arabidopsis correlated with the accumulation of FCCs and NCCs, as well as with an increase in PAO activity. This increase was due to an up-regulation of Pao gene expression. In contrast, red chl catabolite reductase is not regulated during leaf development and senescence. A pao1 knockout mutant was identified and analyzed. The mutant showed an age- and light-dependent cell death phenotype on leaves and in flowers caused by the accumulation of photoreactive pheide a. In the dark, pao1 exhibited a stay-green phenotype. The key role of PAO in chl breakdown is discussed.

Apoptosis Regulatory Proteins↗
PubMed2002

Determination of relative chlorophyll binding affinities in the major light-harvesting chlorophyll a/b complex.

The major light-harvesting complex (LHCIIb) of photosystem II can be reconstituted in vitro from its recombinant apoprotein in the presence of a mixture of carotenoids and chlorophylls a and b. By varying the chlorophyll a/b ratio in the reconstitution mixture, the relative amounts of chlorophyll a and chlorophyll b bound to LHCIIb can be changed. We have analyzed the chlorophyll stoichiometry in recombinant wild type and mutant LHCIIb reconstituted at different chlorophyll a/b ratios in order to assess relative affinities of the chlorophyll-binding sites. This approach reveals five sites that exclusively bind chlorophyll b. Another site exhibits a slight preference of chlorophyll b over chlorophyll a. The remaining six sites are filled preferentially with chlorophyll a but also tolerate chlorophyll b when this is offered at a large excess. Three of these chlorophyll a-affine sites could be assigned to distinct positions defined by the three-dimensional LHCIIb structure. Exclusive chlorophyll b sites complemented by chlorophyll a sites that are selective only to a certain extent are consistent with the observation that chlorophyll b but not chlorophyll a is essential for reconstituting stable LHCIIb. These data offer an explanation why a rather constant chlorophyll a/b ratio is observed in native LHCIIb despite the apparent promiscuity of some binding sites.

Amino Acid Substitution↗
PubMed1987

Chlorophyll-Protein Complexes from the Red-Tide Dinoflagellate, Gonyaulax polyedra Stein : Isolation, Characterization, and the Effect of Growth Irradiance on Chlorophyll Distribution.

A comparision of high (330 microeinsteins per meter squared per second) and low (80 microeinsteins per meter squared per second) light grown Gonyaulax polyedra indicated a change in the distribution of chlorophyll a, chlorophyll c(2), and peridinin among detergent-soluble chlorophyll-protein complexes. Thylakoid fractions were prepared by sonication and centrifugation. Chlorophyll-protein complexes were solubilized from the membranes with sodium dodecyl sulfate and resolved by Deriphat electrophoresis. Low light cells yielded five distinct chlorophyll-protein complexes (I to V), while only four (I' to IV') were evident in preparations of high light cells. Both high molecular weight complexes I and I' were dominated by chlorophyll a absorption and associated with minor amounts of chlorophyll c. Both complexes II and II' were chlorophyll a-chlorophyll c(2)-protein complexes devoid of peridinin and unique to dinoflagellates. The chlorophyll a:c(2) molar ratio of both complexes was 1:3, indicating significant chlorophyll c enrichment over thylakoid membrane chlorophyll a:c ratios of 1.8 to 2:1. Low light complex III differed from all other high or low light complexes in that it possessed peridinin and had a chlorophyll a:c(2) ratio of 1:1. Low light complexes IV and V and high light complexes III' and IV' were spectrally similar, had high chlorophyll a:c(2) ratios (4:1), and were associated with peridinin. The effects of growth irradiance on the composition of chlorophyll-protein complexes in Gonyaulax polyedra differed from those described for other chlorophyll c-containing plant species.

Journal Article↗
PubMed1984

Chlorophyll-Protein Complexes of a Photosystem II Mutant of Maize : Evidence that Chlorophyll-Protein a-2 and a Chlorophyll-Protein Complex Derived from a Photosystem I Antennae System Comigrate on Polyacrylamide Gels.

Use of the octyl beta-d-glucopyranoside solubilization procedure of Camm and Green (1980 Plant Physiol 66: 428-432) reveals that thylakoid membranes of a photosystem (PS) II-deficient maize (Zea mays L.) mutant lack two chlorophyll protein (CP) complexes associated with PSII, i.e. CPa-1 and CPa-2. In contrast, when lithium dodecyl sulfate is used to solubilize the membranes of the mutant prior to electrophoretic separation, a CP complex is observed which has a mobility similar to that of CPa-2. Comparison of spectral characteristics and polypeptide composition of the green bands in this region taken from samples of the mutant, normal sibling control plants and from PSII preparations indicate that the CP complex observed in the mutant represents a portion of a light-harvesting complex of PSI (Mullet et al. 1980 Plant Physiol 65: 814-822). The green band observed in normal maize samples can contain both the CPa-2 complex as well as the CP complex derived from the PSI antennae system.

Journal Article↗
PubMed1978

Analyses of absorption and fluorescence spectra of water-soluble chlorophyll proteins, pigment system II particles and chlorophyll a in diethylether solution by the curve-fitting method.

Absorption and fluorescence spectra in the red region of water-soluble chlorophyll proteins, Lepidium CP661, CP663 and Brassica CP673, pigment System II particles of spinach chloroplasts and chlorophyll a in diethylether solution at 25 degrees C were analyzed by the curve-fitting method (French, C.S., Brown, J.S. and Lawrence, M.C. (1972) Plant Physiol 49, 421--429). It was found that each of the chlorophyll forms of the chlorophyll proteins and the pigment System II particles had a corresponding fluorescence band with the Stokes shift ranging from 0.6 to 4.0 nm. The absorption spectrum of chlorophyll a in diethylether solution was analyzed to one major band with a peak at 660.5 nm and some minor bands, while the fluorescence spectrum was analyzed to one major band with a peak at 664.9 nm and some minor bands. A mirror image was clearly demonstrated between the resolved spectra of absorption and fluorescence. The absorption spectrum of Lepidium CP661 was composed of a chlorophyll b form with a peak at 652.8 nm and two chlorophyll a forms with peaks at 662.6 and 671.9 nm. The fluorescence spectrum was analyzed to five component bands. Three of them with peaks at 654.8, 664.6 and 674.6 nm were attributed to emissions of the three chlorophyll forms with the Stokes shift of 2.0--2.7 nm. The absorption spectrum of Brassica CP673 had a chlorophyll b form with a peak at 653.7 nm and four chlorophyll a forms with peaks at 662.7, 671.3, 676.9 and 684.2 nm. The fluorescence spectrum was resolved into seven component bands. Four of them with peaks at 666.7, 673.1, 677.5 and 686.2 nm corresponded to the four chlorophyll a forms with the Stokes shift of 0.6--4.0 nm. The absorption spectrum of the pigment System II particles had a chlorophyll b form with a peak at 652.4 nm and three chlorophyll a forms with peaks at 662.9, 672.1 and 681.6 nm. The fluorescence spectrum was analyzed to four major component bands with peaks at 674.1, 682.8, 692.0 and 706.7 nm and some minor bands. The former two bands corresponded to the chlorophyll a forms with peaks at 672.1 and 681.6 nm with the Stokes shift of 2.0 and 1.2 nm, respectively. Absorption spectra at 25 degrees C and at --196 degrees C of the water-soluble chlorophyll proteins were compared by the curve-fitting methods. The component bands at --196 degrees C were blue-shifted by 0.8--4.1 nm and narrower in half widths as compared to those at 25 degrees C.

Chlorophyll↗
PubMed1997

Analysis of some optical properties of a native and reconstituted photosystem II antenna complex, CP29: pigment binding sites can be occupied by chlorophyll a or chlorophyll b and determine spectral forms.

The minor photosystem II antenna complex CP29(Lhcb-4) has been reconstituted in vitro with the Lhcb-4 apoprotein, overexpressed in Escherichia coli, and the native pigments. Modulation of the pigment composition during reconstitution yields binding products with markedly different chlorophyll a/b binding ratios even though the total number of bound chlorophylls (a plus b) remains constant at eight. A thermodynamic analysis of steady state absorption and fluorescence spectra demonstrates that all chlorophylls are energetically coupled, while the kinetics of chlorophyll photooxidation indicate that triplet chlorophyll-carotenoid coupling is also conserved during pigment binding in vitro. The influence of the chlorophyll a/b binding ratio on the absorption spectra measured at 72 and 300 K is analyzed for the Qy absorption region. Increased chlorophyll b binding leads to large increases in absorption in the 640-660 nm region, while absorption in the 675-690 nm interval decreases markedly. These changes are analyzed in terms of a Gaussian decomposition description in which the eight subbands display a temperature-dependent broadening in agreement with the weak electron-phonon coupling demonstrated for other antenna chlorophyll spectral forms. In this way, we demonstrate that increased chlorophyll b binding leads to increased absorption intensity associated with the subbands at 640, 648, 655, and 660 nm and decreased intensity for the long wavelength subbands at 678 and 684 nm. The wavelength position of all subbands is unchanged. The above data are interpreted to indicate that CP29 has eight chlorophyll binding sites, many or all of which can be occupied by either chlorophyll a or chlorophyll b according to the conditions in which pigment binding occurs. Chlorophyll b absorption is primarily associated with four subbands located at 640, 648, 655, and 660 nm. The invariance of the wavelength position of the absorption bands in recombinant products with different chlorophyll a/b binding stoichiometries is discussed in terms of the mechanism involved in the formation of spectral bands. We conclude that pigment-protein interactions dominate in the determination of spectral heterogeneity with probably only minor effects on absorption associated with pigment-pigment interactions.

Apoproteins↗
PubMed1994

Chlorophyll regulates accumulation of the plastid-encoded chlorophyll proteins P700 and D1 by increasing apoprotein stability.

Chlorophyll protein accumulation in barley (Hordeum vulgare L.) chloroplasts is controlled posttranscriptionally by light-induced formation of chlorophyll a. The abundance of translation initiation complexes associated with psbA, psaA, and rbcL mRNAs was measured using extension and inhibition analysis in plants grown in the dark for 4.5 d and then illuminated for up to 16 h. Light-induced accumulation of the chlorophyll proteins was not accompanied by changes in the abundance of translation initiation complexes, indicating that regulation of chlorophyll protein accumulation at this stage of development does not occur at the level of translation initiation. Translational runoff assays were performed in the presence of lincomycin, an inhibitor of translation initiation, to determine whether chlorophyll protein accumulation was regulated at the level of translation elongation. The extent of ribosome runoff of psaA and psbA mRNAs was similar in the presence or absence of chlorophyll, indicating that chlorophyll did not alter chlorophyll protein translation elongation. Polysome-associated D1 translation intermediates were radiolabeled in the presence or absence of chlorophyll, even though full-length D1 accumulated only in the presence of chlorophyll. Chlorophyll influenced the stability of D1 translation intermediates to a small extent and greatly increased D1 stability after release from ribosomes. Overall, these results demonstrate that light-induced chlorophyll biosynthesis triggers the accumulation of the chlorophyll proteins D1 and P700 in barley chloroplasts by enhancement of chlorophyll apoprotein stability.

Apoproteins↗