The photochemical activities and electron carriers of developing barley leaves

Intraspecific Variation within the Utricularia amethystina Species Morphotypes Based on Chloroplast Genomes

Utricularia amethystina Salzm. ex A.St.-Hil. & Girard (Lentibulariaceae) is a highly polymorphic carnivorous plant taxonomically rearranged many times throughout history. Herein, the complete chloroplast genomes (cpDNA) of three U. amethystina morphotypes: purple-, white-, and yellow-flowered, were sequenced, compared, and putative markers for systematic, populations, and evolutionary studies were uncovered. In addition, RNA-Seq and RNA-editing analysis were employed for functional cpDNA evaluation. The cpDNA of three U. amethystina morphotypes exhibits typical quadripartite structure. Fine-grained sequence comparison revealed a high degree of intraspecific genetic variability in all morphotypes, including an exclusive inversion in the psbM and petN genes in U. amethystina yellow. Phylogenetic analyses indicate that U. amethystina morphotypes are monophyletic. Furthermore, in contrast to the terrestrial Utricularia reniformis cpDNA, the U. amethystina morphotypes retain all the plastid NAD(P)H-dehydrogenase (ndh) complex genes. This observation supports the hypothesis that the ndhs in terrestrial Utricularia were independently lost and regained, also suggesting that different habitats (aquatic and terrestrial) are not related to the absence of Utricularia ndhs gene repertoire as previously assumed. Moreover, RNA-Seq analyses recovered similar patterns, including nonsynonymous RNA-editing sites (e.g., rps14 and petB). Collectively, our results bring new insights into the chloroplast genome architecture and evolution of the photosynthesis machinery in the Lentibulariaceae.

HPLC determination of photosynthetic pigments during greening of etiolated barley leaves. Evidence for the biosynthesis of chlorophyll a'

The temporal evolution of pigment composition during greening of etiolated barley leaves was investigated by reversed-phase HPLC with particular attention to chlorophyll (Chl) a' (C13(2) epimer of Chl a), which had been detected by ourselves in photosystem (PS) I particles. At early stages of greening, the Chl a'/Chl a molar ratio rapidly increased to a level more than twice that in mature leaves, then gradually leveled off, accompanied by a growth of the Chl b/Chl a ratio, to the mature level. After 3 h of illumination, the temporal evolution of the Chl a'/Chl a molar ratio nearly paralleled that of the P700/Chl a ratio with a stoichiometry Chl a'/P700 approximately equal to 2: this strongly suggests that Chl a' is biosynthesized as a constituent of the PS I reaction center complex.

Photoconversion of long-wavelength protochlorophyll native form Pchl 682/672 into chlorophyll Chl 715/696 in Chlorella vulgaris B-15

By spectral methods, the final stages of chlorophyll formation from protochlorophyll (ide) were studied in heterotrophic cells of Chlorella vulgaris B-15 mutant, where chlorophyll dark biosynthesis is inhibited. It was shown that during the dark cultivation, in the mutant cells, in addition to the well-known protochlorophyll (ide) forms Pchlide 655/650, Pchl(ide) 640/635, Pchl(ide) 633/627, a long-wavelength protochlorophyll form is accumulated with fluorescence maximum at 682 nm and absorption maximum at 672 nm (Pchl 682/672). According to the spectra measured in vivo and in vitro, illumination of dark grown cells leads to the photoconversion of Pchl 682/672 into the stable long wavelength chlorophyll native form Chl 715/696. This reaction was accompanied by well-known photoreactions of shorter-wavelength Pchl (ide) forms: Pchlide 655/650→Chlide 695/684 and Pchl (ide) 640/635→Chl (ide) 680/670. These three photoreactions were observed at room temperature as well as at low temperature (203-233 K).

The pea plastocyanin promoter directs cell-specific but not full light-regulated expression in transgenic tobacco plants

A series of 5' deletions of the pea plastocyanin gene (petE) promoter fused to the beta-glucuronidase (GUS) reporter gene has been examined for expression in transgenic tobacco plants. Strong positive and negative cis-elements which modulate quantitative expression of the transgene in the light and the dark have been detected within the petE promoter. Disruption of a negative regulatory element at -784 bp produced the strongest photosynthesis-gene promoter so far described. Histochemical analysis demonstrated that all petE-GUS constructs directed expression in chloroplast-containing cells, and that a region from -176 bp to +4 bp from the translation start site was sufficient for such cell-specific expression. The petE-promoter fusions were expressed at high levels in etiolated transgenic tobacco seedlings but there was no marked induction of GUS activity in the light. The endogenous tobacco plastocyanin genes and the complete pea plastocyanin gene in transgenic tobacco plants were also expressed in the dark, but showed a three- to sevenfold increase in the light. This indicates a requirement for sequences 3' to the promoter for the full light response of the petE gene.

Cytochrome f: Structure, function and biosynthesis

Cytochrome f is an intrinsic membrane component of the cytochrome bf complex, transferring electrons from the Rieske FeS protein to plastocyanin in the thylakoid lumen. The protein is held in the thylakoid membrane by a single transmembrane span located near its C-terminus with a globular hydrophilic domain extending into the lumen. The globular domain of the turnip protein has recently been crystallised, offering the prospect of a detailed three-dimensional structure. Reaction with plastocyanin involves localised positive charges on cytochrome f interacting with the acidic patch on plastocyanin and electron transfer via the surface-exposed tyrosine residue (Tyr83) of plastocyanin. Apocytochrome f is encoded in the chloroplast genome and is synthesised with an N-terminal presequence which targets the protein to the thylakoid membrane. The synthesis of cytochrome f is coordinated with the synthesis of the other subunits of the cytochrome bf complex.

Effect of Gabaculine on the Synthesis of Heme and Cytochrome f in Etiolated Wheat Seedlings

The effect of gabaculine (3-amino 2,3-dihydrobenzoic acid), an inhibitor of tetrapyrrole synthesis, on the accumulation of heme and cytochrome f in etiolated wheat (Triticum aestivum var Mardler) seedlings has been examined. Gabaculine treatment resulted in decreased amounts of heme and of holocytochrome f detected spectroscopically and by peroxidase activity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amount of the cytochrome f polypeptide detected immunochemically on Western blots was much less affected by gabaculine treatment, indicating that apocytochrome f synthesis was not tightly coupled to heme availability. Gabaculine treatment did not affect the size of the cytochrome f polypeptide, indicating that heme addition is not required for proteolytic removal of the presequence.

Anomalous electron transport activity in a Photosystem I-deficient maize mutant

Photosynthesis mutations were induced in maize lines bearing the transposable DNA element system, Mutator. Two Photosystem I mutants (hcf101 and hcf104) which were isolated are described here. Maize plants homozygous for the hcf104 mutation are seedling lethal and exhibit a high in vivo chlorophyll fluorescence yield. They lack ∼60% of CP1, P700 and PSI-specific electron transport activity relative to normal sibling plants. The comparable depletion of these three measures of PS I content conforms to the pattern reported for many other PS I-deficient mutants. Maize plants homozygous for hcf101 are seedling lethal and also exhibit high in vivo chlorophyll fluorescence yield. They lack 80-90% of CP1 and P700 but sustain steady state levels of PS I-specific electron transport activity at 70% of normal. Previous reports of similar apparent PS I hyperactivity are discussed and an explanation for the elevated steady state level of PS I electron transport activity in hcf101 is proposed.

Electron-transfer events leading to reconstitution of oxygen-evolution activity in manganese-depleted photosystem II membranes

O2-evolution activity and the Mn complex can be reconstituted in photosystem II by a process called photoactivation. We have studied the elementary steps in photoactivation by using electron paramagnetic resonance spectroscopy to probe electron transport in Mn-depleted photosystem II membranes. The electron donation reactions in Mn-depleted photosystem II were found to be identical with those in untreated photosystem II, except that electron donation from the Mn complex was absent and could be replaced by slower electron donation from exogenous Mn2+. Mn2+ photooxidation by Mn-depleted photosystem II membranes correlates with reconstitution of O2-evolution activity. However, photooxidation of Mn2+ occurs in competition with photooxidation of the tyrosine residue YD, and cytochrome b-559. Thus, these two species are excluded from direct participation in the initial steps in the assembly of the Mn complex. Because photooxidation of Mn2+ is slower than photooxidation of the competing electron donors, cytochrome b-559 and chlorophyll, as well as recombination of the charge-separated states chlorophyll+QA- or YZ+QA-, these other reactions dominate in a single photochemical turnover reaction. This provides a molecular basis for both the low yield and low quantum yield of photoactivation. The first photochemical step in the assembly of the Mn complex results in photooxidation of one Mn2+ ion. Therefore, the first intermediate in assembly of the Mn complex contains Mn3+. On the basis of these results and previous kinetic studies [Miller, A.-F., & Brudvig, G. W. (1989) Biochemistry 28, 8181], we conclude that the second intermediate of Mn complex assembly contains Mn2+Mn3+, which is photooxidized to Mn3+2.

Formation of the Photosynthetic Electron Transport System during the Early Phase of Greening in Barley Leaves

The development of photochemical activity in isolated plastids during the early phase of greening of 5-day-old etiolated barley seedlings was studied and related to the appearance of chlorophyll-protein complexes. Photochemical activities of PSI (DCIPH(2) --> MV) and PSII (H(2)O --> DCIP, DPC --> DCIP) appeared at 1 and 1.5 hours after the onset of illumination, respectively. However, PSI + PSII activity (H(2)O --> MV, H(2)O --> NADP) appeared at 4 hours. The functional plastoquinone pool was noticed, at the latest, from 4 hours. Chloroplast preparations from seedlings of 1 h of greening showed O(2) uptake upon illumination in the absence of MV (-MV activity). This activity peaked at 2 hours of greening, then fell to zero by 6 hours. In contrast to the -MV activity, MV-Hill activity began to increase at 2 hours. Although PSI activity appeared at 1 hour, it failed to reduce ferredoxin until 2 hours. NADP began to be photoreduced at 4 hours in accordance with the appearance of the ferredoxin:NADP reductase activity. After formation of PSI and PSII, electron transport systems between them and between PSI and NADP developed in coordination with each other. Thus, the whole electron transport from water to NADP began to operate at 4 hours.

Plastocyanin is encoded by a single-copy gene in the pea haploid genome

cDNA clones for pea plastocyanin were isolated from a pea leaf cDNA library screened with a (32)P-labelled mixed oligonucleotide probe predicted from part of the N-terminal amino acid sequence of pea plastocyanin. The six cDNA clones isolated were found to be identical in the regions in which they overlapped. A Southern blot of restricted pea DNA probed with one of these cDNA clones showed the pea plastocyanin gene to exist as a single copy in the haploid genome. A pea genomic library in λEMBL3 screened with the same cDNA clone gave three positive plaques which contained identical 16 kbp Bam HI fragments. A single uninterrupted plastocyanin gene was located near the middle of the fragment and was characterised by DNA sequencing. The derived amino acid sequence indicates that the plastocyanin precursor consists of 168 amino acid residues including a presequence of 69 amino acid residues. The transcription initiation site was located by S1 nuclease mapping approximately 50 bp upstream of the translation initiation site. A sequence similar to a consensus light-responsive element found in a large number of phytochrome-dependent light-inducible genes is located just upstream of the TATA box. A cluster of direct repeats containing potential Z-DNA-forming elements occurs 600-750 bp upstream of the transcription initiation site.

A photosystem II polypeptide is encoded by an open reading frame co-transcribed with genes for cytochrome b-559 in wheat chloroplast DNA

The N-terminal amino acid sequence of a 3.2 kDa photosystem II polypeptide is shown to be identical to that of a polypeptide encoded by an open reading frame of 38 codons (orf38) in wheat chloroplast DNA. Orf38 is located just downstream of the psbE and psbF genes for the polypeptides of cytochrome b-559. Analysis of the transcription of this region of chloroplast DNA shows that psbE, psbF and orf38 are co-transcribed to give a 1.1 kb polycistronic transcript which also contains another open reading frame of 40 codons. The orf38 and orf40 products are hydrophobic polypeptides which are both predicted to span the thylakoid membrane once. Orf38 and orf40 are highly conserved, and map to similar locations adjacent to psbE and psbF, in all organisms from which this region of DNA has been sequenced. We propose that orf38 is named psbL.

Synthesis and assembly of the cytochrome b-f complex in higher plants

The cytochrome b-f complex is composed of four polypeptide subunits, three of which, cytochrome f, cytochrome b-563 and subunit IV, are encoded in chloroplast DNA and synthesised within the chloroplast, and the fourth, the Rieske FeS protein, is encoded in nuclear DNA and synthesised in the cytoplasm. The assembly of the cytochrome b-f complex therefore requires the interaction of subunits encoded by different genomes. A key role for the nuclear-encoded Rieske FeS protein in the assembly of the complex is suggested by a study of cytochrome b-f complex mutants. The assembly of individual subunits of the complex may be regulated by the availability of prosthetic groups. The genes for the chloroplast-encoded subunits and cDNA clones for the Rieske FeS protein have been isolated and characterised. Cytochrome f and the Rieske FeS protein are synthesised initially with N-terminal presequences required for their correct assembly within the chloroplast. The deduced amino acid sequences of the four subunits have been used to suggest models for the arrangement of the polypeptides in the thylakoid membrane.

Characterization of the barley chloroplast transcription units containing psaA-psaB and psbD-psbC

Four plastid genes, psaA, psaB, psbD and psbC, were localized on the barley plastid genome. PsaA was adjacent to psaB in one transcription unit and psbD was adjacent to psbC in a second transcription unit. The transcription units containing psaA-psaB and psbD-psbC are separated by approximately 25 kbp on the barley plastid genome and are transcribed convergently. Transcripts hybridizing to each transcription unit were characterized by northern blot analysis, S1 protection experiments and primer extension analysis. Two 5.3 kb transcripts hybridize to psaA-psaB. The two transcripts have a common 5' end but differ at their 3' ends by about 26 nucleotides. The transcription unit which contains psbD-psbC also includes trnS(UGA), trnG(GCC), and an open reading frame which codes for a 62 amino acid protein. Six large transcripts ranging from 5.7 kb to 1.7 kb hybridize to the psbD-psbC transcription unit as well as several RNAs of tRNA size. The large transcripts arise from three 5' ends and two clusters of 3' ends. The 3' ends map near trnG(GCC) and trnS(UGA) and could be generated by RNA processing or termination of transcription. Two of the six transcripts hybridize to psbC but not psbD suggesting that translation of psbD and psbC could occur on separate RNAs.

PHOTOSYNTHETIC AND RESPIRATORY CHARACTERISTICS OF MALAYAN SUN AND SHADE FERNS

A comparative study of four Malayan ferns, Christensenia aesculifolia (Bl.) Maxon, Tectaria singaporeana (Wall.) Ching, Abacopteris multilineata (Wall.) Ching and Hymenophyllum polyanthos Sw. from shady habitats and another four, Dicranopteris linearis (Burm.) Und., Lygodium scandens (L.) Sw., Blechnum orientate Linn, and Stenochlaena palustris (Burm.) Bedd. from sunlit habitats showed that the total chlorophyll content expressed on a gram fresh weight basis was greater in the shade ferns. There was little difference in the chlorophyll content between the sun and shade ferns when it was expressed on a per unit leaf area basis. The protein and protohaem content was greater in the sun ferns. Measurements of the in vitro photochemical activities of the photosystems I and II in isolated chloroplasts by means of an oxygen electrode showed higher rates in the sun ferns. As determined by spectrophotometric analysis, the photosynthetic cytochrome content from isolated chloroplasts was greater in the sun ferns. The results indicate that the sun ferns have physiological characteristics favouring greater capacity for photosynthesis. Mitochondria isolated from the sun ferns showed faster rates of electron transport using exogenous NADH as substrate.

Biosynthesis of P700-Chlorophyll a Protein Complex, Plastocyanin, and Cytochrome b(6)/f Complex

Changes in the amount of P700-chlorophyll a protein complex, plastocyanin, and cytochrome b(6)/f complex during greening of pea (Pisum sativum L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) leaves were analyzed by an immunochemical quantification method. Neither subunit I nor II of P700-chlorophyll a protein complex could be detected in the etiolated seedlings of all three plants and the accumulation of these subunits was shown to be light dependent. On the other hand, a small amount of plastocyanin was present in the etiolated seedlings of all three plants and its level increased about 30-fold during the subsequent 72-hour greening period. Furthermore, cytochrome f, cytochrome b(6), and Rieske Fe-S center protein in cytochrome b(6)/f complex were also present in the etiolated seedings of all three plants. The level of each subunit component increased differently during greening and their induction pattern differed from species to species. The accumulation of cytochrome b(6)/f complex was most profoundly affected by light in pea leaves, and the levels of cytochrome f, cytochrome b(6), and Rieske Fe-S center protein increased during greening about 10-, 20-, and more than 30-fold, respectively. In comparison to the case of pea seedlings, in wheat and barley leaves the level of each subunit component increased much less markedly. The results suggest that light regulates the accumulation of not only the chlorophyll protein complex but also the components of the electron transport systems.

Photosynthetic characteristics of detached barley leaves during greening in the presence of SAN 9785

The effects of the pyridazinone compound SAN 9785 on the photosynthetic competence of leaves, on the photochemical activity of isolated thylakoids and on the formation and spectral properties of chlorophyll-protein complexes were studied during a 72-h greening period of detached etiolated leaves of barley (Hordeum vulgare L. cv. Horpácsi kétsoros). It was established that i) the photosynthetic capacity of the leaves decreased considerably (by 80 and 90%, as determined by(14)CO2 fixation and fast fluorescence induction measurements, respectively); ii) the photochemical activity of isolated thylakoids from water to potassium ferricyanide and from dichlorophenol indophenol/ascorbate to methylviologen exhibited only slight reductions when expressed on a chlorophyll basis compared with the control; iii) the slow fluorescence induction curves of the treated leaves demonstrated the presence of a peculiar fluorescence component interrupting the quenching of fluorescence at around 1 min illumination; iv) a shortage of the chlorophyll-protein complex of photosystem I (CPI) occurred with a higher content of the monomer of the light harvesting complex in the thylakoids of treated leaves; and v) the fluorescence spectrum of the CPI band present in treated leaves indicates the destruction of the structural integrity of this complex during isolation from the membrane.

Chlorophyll-protein complex composition and photochemical activity in developing chloroplasts from greening barley seedlings

The time course for the observation of intact chlorophyll-protein (CP) complexes during barley chloroplast development was measured by mild sodium dodecyl sulfate polyacrylamide gel electrophoresis. The procedure required extraction of thylakoid membranes with sodium bromide to remove extrinsic proteins. During the early stages of greening, the proteins extracted with sodium bromide included polypeptides from the cell nucleus that associate with developing thylakoid membranes during isolation and interfere with the separation of CP complexes by electrophoresis. Photosystem I CP complexes were observed before the photosystem II and light-harvesting CP complexes during the initial stages of barley chloroplast development. Photosystem I activity was observed before the photosystem I CP complex was detected whereas photosystem II activity coincided with the appearance of the CP complex associated with photosystem II. Throughout chloroplast development, the percentage of the total chlorophyll associated with photosystem I remained constant whereas the amount of chlorophyll associated with photosystem II and the light-harvesting complex increased. The CP composition of thylakoid membranes from the early stages of greening was difficult to quantitate because a large amount of chlorophyll was released from the CP complexes during detergent extraction. As chloroplast development proceeded, a decrease was observed in the amount of chlorophyll released from the CP complexes by detergent action. The decrease suggested that the CP complexes were stabilized during the later stages of development.

Biogenesis of photosystem I reaction center during greening of oat, bean and spinach leaves

The relative amounts of some chloroplast polypeptides were followed during greening of leaves from three different plant families. Oat, bean and spinach were the representatives of the Gramineae, Leguminosae and Chenopodiaceae, respectively. By using specific antibodies against subunits of the chloroplast protein complexes, it was found with that method that the protein complexes which are not involved in a photobiochemical reaction were synthesized in etiolated leaves and their amounts did not significantly change during greening. Examples of these are the large and small subunits of ribulose 1,5-bisphosphate carboxylase, the subunits of the chloroplast coupling factor (CF1) and cytochrome b6-f complex. On the other hand, in photosystem I reaction center, the synthesis of subunits II, III, IV and V was found to be induced by light. Sequential synthesis of these subunits was observed. Subunit II is the first to be synthesized after exposing the plants to light. The synthesis of subunits III, IV and V followed the synthesis of subunit II in this order. Subunit I of photosystem I reaction center was present in etiolated leaves and its amount was not significantly altered during the first few hours of greening.

Synthesis of components of the cytochrome b-f complex by isolated pea chloroplasts

Three components of the cytochrome b-f complex, cytochrome f, cytochrome b-563 and a 15.2-kDa polypeptide, were labelled with radioactive amino acids in isolated pea chloroplasts incubated in the light with added Mg-ATP. The assembly of cytochrome b-563 (19.5 kDa) into the cytochrome complex required the presence of added Mg-ATP whereas cytochrome f (37.3 kDa) and the 15.2-kDa polypeptide were assembled in its absence. Incorporation of [35S]methionine into the polypeptide chain of cytochrome b-563 and the 15.2-kDa component was confirmed by peptide mapping of the products of partial digestion with papain.

Protein synthesis during chloroplast development in Spirodela oligorhiza. Coordinated synthesis of chloroplast-encoded and nuclear-encoded subunits of ATPase and ribulose-1,5-bisphosphate carboxylase

We have studied qualitative and quantitative changes of several parameters during chloroplast development in Spirodela oligorhiza (duckweed). On a dry weight basis, the amount of protein increases from 2.5% (w/w) in dark-grown to 7.8% (w/w) in light-grown fronds. At the same time the amount of starch drops from 50% to 27% (w/w). Using an immunochemical quantification method we have found that during greening of etiolated plants the amount of all subunits of the ATPase complex per frond increases 10-fold, whereas the level of the subunits of ribulose-1,5-biphosphate carboxylase increases 50-fold. Cytochrome f was found to be present in dark-grown Spirodela and the amount of this polypeptide per frond increases about 30-fold. The concentration of a polypeptide that possibly represents a cytochrome b6 subunit increases about 10-fold upon greening. The molar ratio of the CF1-beta and CF1-gamma subunits of the ATPase complex varies over 2-3, while in all stages of chloroplast development studied the molar ratio of the carboxylase subunits is about 1. As these values are in agreement with the stoichiometrical amounts in the native protein complexes, we conclude that the synthesis of CF1-beta and CF1-gamma, as well as the synthesis of the large and small carboxylase subunits, are strictly coordinated during chloroplast biogenesis in Spirodela oligorhiza.

Thylakoid protein kinase activity and associated control of excitation energy distribution during chloroplast biogenesis in wheat

The activity of thylakoid protein kinase and the regulation of excitation energy distribution between photosystems I and II was examined during chloroplast biogenesis in light-grown Triticum aestivum (wheat) leaves. The specific activity of the thylakoid protein kinase decreased some six-fold during development from the young plastids at the base of the 7-d-old leaf to the mature chloroplasts at the leaf tip. Appreciable activity was also detected in plastids isolated from etiolated leaves. In mature chloroplasts the majority of phosphate was incorporated into the Mr=26,000 apo-proteins of the light-harvesting chlorophyll a/b-protein complex (LHCP). However, at early stages of chloroplast development and in the etioplast, the phosphate was predominantly incorporated into a polypeptide of Mr=9,000 dalton. Immature thylakoids, isolated from the base of the leaf, had relatively low concentrations of LHCP and could perform a State 1-State 2 transition, as demonstrated by ATP-induced quenching of photosystem II fluorescence. Analyses of photosystem I and photosystem II fluorescence-induction curves from intact leaf tissue demonstrated that this transition occurs in vivo at early stages of leaf development and, therefore, may play an important role in regulating energy transduction during chloroplast biogenesis.

Cooperation of cytoplasmic and plastidial translation in formation of the photosynthetic apparatus and its stage-specific efficiency

In synchronized Euglena gracilis, strain Z, the synthesis of the apoproteins for the chlorophyll-protein-complexes CPI, CPa, and LHCP is light-dependent and takes place in the light period in a characteristic consecutive fashion: CPI at 1 to 2 hours, CPa at 7 to 12 hours, and LHCP at 8 to 12 hours. The syntheses sequence of the chlorophyll-protein-complexes coincides with the efficiency alterations of the photosynthetic apparatus of E. gracilis during the light period of the cell cycle. In particular, the synthesis onset of the photosystem II-related polypeptides CPa and LHCP aligns with the decrease of oxygen evolution at 6 hours of the light period and is discussed as reorganization process in the thylakoids.

Rate-Limiting Steps of Electron Transport in Chloroplasts during Ontogeny and Senescence of Barley

Partial photochemical activities and concentrations of electron carriers were measured relative to chlorophyll in barley (Hordeum vulgare L.) thylakoids, isolated from primary leaves during ontogeny and senescence. Thylakoids from mature leaves generated somewhat higher quantum efficiencies than thylakoids from premature or senescing leaves; this phenomenon did not appear to be caused by any deficiency of water-splitting enzyme. Under conditions of saturating light, the noncyclic electron flux from water to the reducing side of photosystem I increased during leaf ontogeny, peaked at maturity, and declined during senescence. However, electron fluxes appeared to be limited at different steps before and after leaf maturity. Before leaf maturity, the rate-limiting step was located prior to the reoxidation of plastohydroquinone. After leaf maturity, the decline in noncyclic electron flux correlated with a decrease in the concentration of cytochromes f and b(6). This correlation, together with a consideration of mechanisms of entry and exit of electrons in 3-(3,4-dichlorophenyl)-1,1-dimethylurea-treated thylakoids, suggests that the cytochrome f/b(6)-containing complex, and not plastocyanin or P700, is the site of entry of electrons from the reduced forms of 2,6-dichlorophenolindophenol and diaminodurene. It is therefore proposed that in senescing leaves the cytochrome f/b(6)-containing complex limited electron transport by constraining the rate of reduction of cytochrome f by plastohydroquinone.

Iron nutrition-mediated chloroplast development

Membrane development in chloroplasts was explored by resupplying iron to iron-deficient sugar beet (Beta vulgaris L. cv F58-554H1) and monitoring changes in lamellar components during regreening. The synthesis of chlorophyll a, chlorophyll b, and Q, the first stable electron acceptor of photosystem II, exhibited a lag phase during the first 24 to 48 hours of resupply. In contrast, the per area amounts of P(700) and cytochrome f increased linearly over the first 48 hours. During the early regreening period, the Q to P(700) ratio was 2.6 and decreased to 0.7 after 96 hours of regreening. The rate of photosynthesis (net CO(2) uptake) per chlorophyll increased during the first 48 hours of resupply, then by 96 hours decreased to values typical of control plants. The results suggest that there was preferential synthesis of the measured photosystem I components during the first 24 to 48 hours, while from 48 to 96 hours there was rapid synthesis of all components. The iron nutrition-mediated chloroplast development system provides a useful experimental approach for studying biomembrane synthesis and structural-functional relations of the photosynthetic apparatus.

Development of photochemical activity in relation to pigment and membrane protein accumulation in chloroplasts of barley and its virescens mutant

The development of photochemical activity in relation to pigment and membrane protein accumulation in chloroplasts of greening wild-type barley (Hordeum vulgare L. cv. Gateway) and its virescens mutant were studied. The rate of chlorophyll accumulation per plastid was faster in the wild-type than in the mutant seedlings upon illumination after 6 days of etiolation, but was not different after 8 days. Although the protein content per plastid did not vary during greening, there was a change in the sodium dodecyl sulfate-polyacrylamide gel polypeptide profiles. High molecular weight proteins of 96,000 and 66,000 decreased whereas those at 34,000, 27,000 and 22,000 increased in relative quantity as a function of greening. The fully greened mutant seedlings were not deficient in the light-harvesting chlorophyll protein complex (LHC) or the reaction centers of photosystem I and photosystem II. Photosystem I-associated photochemical activities appeared within the first hour of plastid development and photosystem II associated activities and O(2) evolution within the next 6 hours. In all cases, the developmental rates per unit protein were slower in the mutant following 6 days of etiolation, but no differences between the two genotypes could be seen after 8 days due to a decrease in the developmental rate of the wild-type chloroplasts. An increase in photosynthetic unit size associated with plastid morphogenesis was faster in the wild-type seedlings after 6 days, but again the difference was negligible after 8 days. It was concluded that no single measured photochemical parameter is affected by this mutation, but rather, all aspects of chloroplast development are affected similarly by an overall reduction in the rate of chloroplast morphogenesis. This mutant, therefore, undergoes the normal pattern of proplastid to chloroplast development, but at a markedly reduced rate.

Light-induced increase in the number and activity of ribosomes bound to pea chloroplast thylakoids in vivo

Within 8 to 10 minutes of illumination, chloroplast thylakoids of pea (Pisum sativum) became enriched 30 to 100% in ribosomes bound by nascent chains. Following (or, in some experiments, coincident with) this apprarent redistribution was a 25 to 65% increase in the total bound ribosome population, which was then maintained at this higher level during the normal light period. On transfer of plants to darkness, the bound ribosome population decreased to the lower dark level. White, blue (400 to 520 nanometers), and orange (545 to 690 nanometers) light were all effective in producing an increase in the bound ribosome population. The level of bound ribosomes in the oldest leaves of 16-day-old plants was 15-fold less than in the still-maturing leaf but was still increased by illumination.In vivo experiments with chloramphenicol and lincomycin indicated a requirement for protein synthesis by the 70S ribosomes both for the light-induced shift to the population bound by nascent chains and for the increase in the total thylakoid-bound population. When thylakoids from plants in darkness or exposed to light for increasing periods were incubated in an Eschericia coli cell-free protein synthesizing system, 15 minutes of prior illumination in vivo produced a 60% increase in [(3)H]leucine incorporation. This stimulation preceded the increase in total bound ribosomes but corresponded in time to observed increases in the ribosomes bound by nascent chains.A light intensity of 100 micromoles per meter(2) per second, but not 25 micromoles per meter(2) per second, caused a significant increase in bound ribosomes over a 30-minute period. Strong inhibition in vivo by 3',4'-dichlorophenyl-1, 1-dimethylurea suggests that noncyclic electron flow is essential for light-induced ribosome redistribution.

Appearance of photochemical function in prothylakoids during plastid development

1. A method to separate the vesicles of prothylakoids from prolamellar body preparations obtained from etiolated and rapidly greening Avena laminae (0.25--4 h illumination ) is described. The prothylakoid preparations were found to be free from contaminating prolamellar bodies but enriched prolamellar body preparations (enriched prolamellar body preparations) still contained some adhering prothylakoid material. 2. Only existing beta-carotene appears to be transferred from the prolamellar bodies to the prothylakoids during early development and this ceases when freshly synthesized beta-carotene becomes available. 3. Prolamellar body structures proper show no positive association of existing or developing photochemical activities; these are only to be found in the developing prothylakoids. 4. Using methylviologen-linked electron transport-dependent oxygen consumption, Photosystem I activities may be detected with added diaminodurene within 15 min of illumination and within 30 min and 1 h with added tetramethylphenylenediamine and dichlorophenolindophenol, respectively. 5. During the 2nd, and 3rd. h of greening, proton-pumping capability and later ATP formation increased in prothylakoids in the presence of diaminodurene. 6. The first indications of Photosystem II activity using diphenylcarbazide as electron donor are shown at a similar time (2 h) with prothylakoids. The last photochemical activity to appear is the capacity to split water (3 h) and consequently the diphenylcarbazide activity diminished to zero before 8 h of illumination have passed. 7. The lack of effect of uncouplers such as NH4+ prior to 2 h suggests that in spite of some proton-pumping ability there is the possibility of proton-leaky areas existing within prothylakoids. This lack of a persistent proton gradient before 2 h of illumination may explain the different starting times of phenazine methosulfate- and diaminodurene-dependent photophosphorylation (0.25 and 2 h, respectively).

Cytochrome f function in photosynthetic electron transport

The questions of whether the stoichiometry of the turnover of cytochrome f, and the time-course of its reduction subsequent to a light flash, are consistent with efficient function in noncyclic electron transport have been investigated. Measurements were made of the absorbance change at the 553-nm alpha-band maximum relative to a reference wavelength. In the dark cytochrome f is initially fully reduced, oxidized by a 0.3-s flash, and reduced again in the dark period after the flash. In the presence of gramicidin at 18 degrees C, the dark reduction was characterized by a half-time of 25-30 ms, stoichiometries of cytochrome f:chlorophyll and P700:chlorophyll of 1:670 and 1:640, respectively, and a short time delay. The time delay in the dark reduction of cytochrome f, which is expected for a component in an intermediate position in the chain, becomes more apparent in the presence of valinomycin and K+. Under these conditions the half-time for cytochrome f dark reduction is 130-150 ms, and the delay is approximately equal to 20 ms. The measured value for the activation energy of the dark reduction of cytochrome f (11 +/- 1 kcal/mol) is the same as that for noncyclic electron transport in steady-state light. A sigmoidal time-course for the reduction of cytochrome f has been calculated for a simple linear electron transport chain. The kinetics for reduction of cytochrome f predicted by the calculation, in the presence of valinomycin and K+, are in reasonably good agreement with the experimental data. There is an appreciable amount of data in the literature to document complex properties of cytochrome f after illumination with short flashes, and evidence for complexity in a light-minus-dark transition. The data presented here, obtained after a long flash that should establish steady-state conditions, either fulfill or are consistent with the basic criteria for efficient function of cytochrome f in noncyclic electron transport.

Interaction of Chloroplasts with Inhibitors: Location of Carotenoid Synthesis and Inhibition during Chloroplast Development

The inhibitor SAN 6706 [4-chloro-5-(dimethylamino)-2-(alpha,alpha,alpha,-trifluoro- m-tolyl-3(2H)-pyridazinone] has been used to study the synthesis of carotenes and xanthophylls during the conversion of etioplasts to chloroplasts in developing barley (Hordeum vulgare) shoots. SAN 6706 inhibits carotenoid synthesis and causes an accumulation of phytoene, but it is also a potent inhibitor of chloroplast electron transport. When developing barley is treated with SAN 6706, carotenoid synthesis is inhibited but total photosynthesis is unaffected. The ability of SAN 6706 to inhibit carotenoid synthesis becomes progressively less if etiolated shoots are illuminated for increasing lengths of time before treatment. During the greening of treated barley shoots only light-induced beta-carotene synthesis is immediately inhibited; xanthophyll synthesis is not affected until after about 8 hours. The hypothesis that SAN 6706 cannot enter the chloroplast but inhibits carotenoid synthesis from the cytoplasm is discussed, and the question as to whether there are not two separate groups of enzymes for the synthesis of carotenes and xanthophylls is considered.

Changes in Chloroplast Membrane Lipids during Adaptation of Barley to Extreme Salinity

During adaptation of barley (Hordeum vulgare L.) seedlings to extremely high concentrations of sodium chloride in the root space, the content of galactolipids of chloroplast membranes decreased considerably. Alterations in membrane lipids were due to the high concentration of ions rather than to the increase in the water potential. Sodium chloride was accumulated in the leaf cells and affected lipid-synthesizing enzymes such as galactosyl transferase and acylase which are attached to the chloroplast envelope. The return of salt-adapted barley seedlings to a nutrient solution with low salt concentration resulted in a reversal of the observed changes. It is suggested that the decrease in content of galactolipids in biomembranes is one of the factors causing increased salt resistance in barley plants which are adapted to extreme salinity.

Interactions between photosystem II components in chloroplast membranes. A correlation between the existence of a low potential species of cytochrome b-559 and low chlorophyll fluorescence in inhibited and developing chloroplasts

1. Chloroplasts inhibited by incubation with hydroxylamine in the light exhibit a low fluorescence yield upon illumination in the presence of dithionite sufficient to completely reduce the primary acceptor, Q. In the absence of magnesium ions, the fluorescence yield is the same as in control chloroplasts, suggesting that the reason for the low yield is a defect in the mechanism by which Mg2+ enhances the fluorescence. These chloroplasts were previouly shown to contain only low potential (Em7.8 = +80 mV) cytochrome b-559 (Horton, P. and Croze, E (1977) Biochim. Biophys. Acta 462, 86-101). 2. In Photosystem II particles, in heat-treated chloroplasts and in trypsin-digested chloroplasts, high potential cytochrome b-559 is absent and the variable fluorescence yield is again low. 3. Peas grown under intermittent light contain only one-fifth of the content of high potential cytochrome b-559 seen in fully greened plants, yet show high rates of water to methyl viologen electron transport. Aquisition of the high potential cytochrome b-559 accompanies synthesis of chlorophyll b, the onset of Mg-stimulated fluorescence and an increased variable yield of fluorescence. A similar correlation was seen during greening of dark-grown barley. 4. It is proposed that the high potential state of cytochrome b-559 is due to the same membrane properties which allow cation enhanced variable fluorescence, so that the presence of low potential cytochrome b-559 is accompanied by a decrease in variable fluorescence yield.

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. II. Formation of system II photosynthetic units during greening under optimal light intensity

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a long lag phase. (2) As a consequence, the chlorophyll reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperatively between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.

Characterization of protoheme levels in etiolated and greening plant tissues

The protoheme content of etiolated, greening, and fully greened bean (Phaseolus vulgaris L. var. Light Red Kidney) leaves has been studied. The protoheme level in etiolated and fully greened leaf tissue stays relatively constant from age 7 to 14 days. In agreement with the studies reported for barley (Castelfranco and Jones 1975 Plant Physiol 55: 485-490), the protoheme content of greening bean and barley (Hordeum vulgare var. Larker) leaves does not change appreciably during the first 9 hours of illumination, but the level rises significantly by the 24th hour of illumination (cf. Hendry and Stobart 1977 Phytochemistry 16: 1545-1548). This increase also occurs in seedlings returned to the dark for 24 to 48 hours following a 10-minute pulse of light. These results demonstrate a limited correlation with previous studies on the development of b-type cytochromes during greening of these tissues (Gregory and Bradbeer 1973; Planta 109: 317-326).

Development of Photosystem I and Photosystem II Activities in Leaves of Light-grown Maize (Zea mays)

To compare chloroplast development in a normally grown plant with etiochloroplast development, green maize plants (Zea mays), grown under a diurnal light regime (16-hour day) were harvested 7 days after sowing and chloroplast biogenesis within the leaf tissue was examined. Determination of total chlorophyll content, ratio of chlorophyll a to chlorophyll b, and O(2)-evolving capacity were made for intact leaf tissue. Plastids at different stages of development were isolated and the electron-transporting capacities of photosystem I and photosystem II measured. Light saturation curves were produced for O(2)-evolving capacity of intact leaf tissue and for photosystem I and photosystem II activities of isolated plastids. Structural studies were also made on the developing plastids. The results indicate that the light-harvesting apparatus becomes increasingly efficient during plastid development due to an increase in the photosynthetic unit size. Photosystem I development is completed before that of photosystem II. Increases in O(2)-evolving capacity during plastid development can be correlated with increased thylakoid fusion. The pattern of photosynthetic membrane development in the light-grown maize plastids is similar to that found in greening etiochloroplasts.

Appearance of Membrane-bound Iron-Sulfur Centers and the Photosystem I Reaction Center during Greening of Barley Leaves

Dark-grown barley (Hordeum vulgare) etioplasts were examined for their content of membrane-bound iron-sulfur centers by electron paramagnetic resonance spectroscopy at 15K. They were found to contain the high potential iron-sulfur center characterized (in the reduced state) by an electron paramagnetic resonance g value of 1.89 (the "Rieske" center) but did not contain any low potential iron-sulfur centers. Per mole of cytochrome f, dark-grown etioplasts and fully developed chloroplasts had the same content of the Rieske center. During greening of etioplasts under continuous light, low potential bound iron-sulfur centers appear. In addition, the photosystem I reaction center, as measured by the photooxidation of P700 at 15K, also became functional; during greening the appearance of a photoreducible low potential iron-sulfur center paralleled the appearance of P700 photoactivity.These findings indicate the close association of the low potential iron-sulfur centers with the photosystem I reaction center; they also support the concept that the development of stable charge separation in the photosystem I reaction center requires, in addition to P700, a low potential iron-sulfur center.