Incompetence of dark-synthesized phycocyanin in excitation transfer to photosystem II chlorophyll

Summary When cells of Anabaena variabilis, all the phycobilin pigments of which had been newly synthesized in the dark, were excited by light absorbed in phycocyanin, the fluorescence emission spectrum showed a peak corresponding to the emission from allophycocyanin, but no emission from chlorophyll. These cells were active in photosynthesis and, when excited by light absorbed by chlorophyll, the emitted fluorescence was characteristic of photosystem II chlorophyll. This indicates that dark synthesized phycocyanin is capable of excitation transfer to allophycocyanin but not to photosystem II chlorophyll.Abbreviation CMU 3-(p-chlorophenyl)-1,1-dimethylurea     

The effect of N-methylprotoporphyrin IX on the synthesis of photosynthetic pigments in Cyanidium caldarium. Further evidence for the role of haem in the biosynthesis of plant bilins

N-Methylprotoporphyrin IX strongly inhibits synthesis of phycocyanobilin, but not chlorophyll a, in the dark. In the light, both phycocyanin and chlorophyll a synthesis are inhibited in parallel. These results are consistent with the intermediacy of haem in algal bilin synthesis and suggest a control mechanism for chlorophyll a synthesis, previously unknown.     

Revised classification of the Cyanidiophyceae based on plastid genome data with descriptions of the Cavernulicolales ord. nov. and Galdieriales ord. nov. (Rhodophyta)

The Cyanidiophyceae, an extremophilic red algal class, is distributed worldwide in extreme environments. Species grow either in acidic hot environments or in dim light conditions (e.g., “cave Cyanidium”). The taxonomy and classification systems are currently based on morphological, eco-physiological, and molecular phylogenetic characters; however, previous phylogenetic results showed hidden diversity of the Cyanidiophyceae and suggested a revision of the classification system. To clarify phylogenetic relationships within this red algal class, we employ a phylogenomic approach based on 15 plastomes (10 new) and 15 mitogenomes (seven new). Our phylogenies show consistent relationships among four lineages (Galdieria, “cave Cyanidium”, Cyanidium, and Cyanidioschyzon lineages). Each lineage is distinguished by organellar genome characteristics. The “cave Cyanidium” lineage is a distinct clade that diverged after the Galdieria clade but within a larger monophyletic clade that included the Cyanidium and Cyanidioschyzon lineages. Because the “cave Cyanidium” lineage is a mesophilic lineage that differs substantially from the other three thermoacidophilic lineages, we describe it as a new order (Cavernulicolales). Based on this evidence, we reclassified the Cyanidiophyceae into four orders: Cyanidiales, Cyanidioschyzonales, Cavernulicolales ord. nov., and Galdieriales ord. nov. The genetic distance among these four orders is comparable to, or greater than, the distances found between other red algal orders and subclasses. Three new genera (Cavernulicola, Gronococcus, Sciadococcus), five new species (Galdieria javensis, Galdieria phlegrea, Galdieria yellowstonensis, Gronococcus sybilensis, Sciadococcus taiwanensis), and a new nomenclatural combination (Cavernulicola chilensis) are proposed.     

Changes in the photosynthetic apparatus in the cyanobacterium Synechocystis sp. PCC 6714 following light-to-dark and dark-to-light transitions

The photosynthetic apparatus of Synechocystis sp. PCC 6714 cells grown chemoheterotrophically (dark with glucose as a carbon source) and photoautotrophically (light in a mineral medium) were compared. Dark-grown cells show a decrease in phycocyanin content and an even greater decrease in chlorophyll content with respect to light-grown cells. Analysis of fluorescence emission spectra at 77 K and at 20 °C, of dark- and light-grown cells, and of phycobilisomes isolated from both types of cells, indicated that in darkness the phycobiliproteins were assembled in functional phycobilisomes (PBS). The dark synthesized PBS, however, were unable to transfer their excitation energy to PS II chlorophyll. Upon illumination of dark-grown cells, recovery of photosynthetic activity, pigment content and energy transfer between PBS and PS II was achieved in 24–48 h according to various steps. For O₂ evolution the initial step was independent of protein synthesis, but the later steps needed de novo synthesis. Concerning recovery of PBS to PS II energy transfer, light seems to be necessary, but neither PS II functioning nor de novo protein synthesis were required. Similarly, light, rather than functional PS II, was important for the recovery of an efficient energy transfer in nitrate-starved cells upon readdition of nitrate. In addition, it has been shown that normal phycobilisomes could accumulate in a Synechocystis sp. PCC 6803 mutant deficient in Photosystem II activity.Abbreviations APC allophycocyanin - CAP chloroamphenicol - Chl chlorophyll - DCMU 3(3,4-dichlorophenyl)-1,1-dimethylurea - CP-47 chlorophyll-binding Photosystem II protein of 47 kDa - EF exoplasmic face - PBS phycobilisome - PC phycocyanin - PS Photosystem     

Metabolism of Oat Leaves during Senescence : VII. The Interaction of Carbon Dioxide and Other Atmospheric Gases with Light in Controlling Chlorophyll Loss and Senescence

In air largely freed from CO₂, senescence of isolated oat (Avena sativa cv Victory) seedling leaves is no longer prevented by white light; instead, the leaves lose both chlorophyll and protein as rapidly as in the dark. Senescence in light is also accelerated in pure O₂, but it is greatly delayed in N₂; 100% N₂ preserves both protein and chlorophyll in light and in darkness. In light in air, most of the compounds tested that had previously been found to delay or inhibit senescence in darkness actually promote the loss of chlorophyll, but they do not promote proteolysis. Under these conditions, proteolysis can therefore be separated from chlorophyll loss. But in light minus CO₂, where chlorophyll loss is rapid in controls, two of these same reagents prevent the chlorophyll loss. Unlike the many reagents whose action in light is thus the opposite of that in darkness, abscisic acid, which promotes chlorophyll loss in the dark, also promotes it in light with or without CO₂. Kinetin, which prevents chlorophyll loss in the dark, also prevents it in light minus CO₂. In general, therefore, the responses to light minus CO₂ are similar to the responses to darkness, and (with the exception of abscisic acid and kinetin) opposite to the response to light in air.     

Photosynthetic oxygen production and the size of the photosynthetic unit in a cell-free preparation from Cyanidium caldarium

A cell-free preparation has been isolated from a mutant of Cyanidium caldarium, grown under conditions such that there is 15 times less chlorophyll per photosynthetic unit than in normal green algae. The preparation is sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea and shows the well-characterized oscillation of O₂ yield, from saturating flashes, following a period of dark adaptation. Greening experiments with dark-grown, wild-type Cyanidium show that the synthesis of photosynthetic units precedes that of bulk chlorophyll and that the O₂-producing system is assembled before the total system coupled to CO₂. No large-scale cooperation of chlorophyll molecules is required for O₂ production.     

A Biochemical Study of Spore Germination in the Blue-green Alga Anabaena doliolum

The spores of Anabaena doliolum formed in light (light spores)and after transfer to darkness (dark spores) are biochemicallydifferent in that the light spores contain chlorophyll a andphycocyanin, while dark spores seem to lack them. The apparentbiosyntheses accompanying dark-spore germination seem to proceedin the following order: RNA, chlorophyll a, phycocyanin andDNA. Results of chloramphenicol treatment indicate that proteinsynthesis precedes RNA synthesis. The biosynthetic events followingRNA synthesis show a requirement for light.     

Acclimation Processes in the Light-Harvesting System of the Cyanobacterium Anacystis nidulans following a Light Shift from White to Red Light

Cyanobacteria acclimate to changes in light by adjusting the amounts of different cellular compounds, for example the light-harvesting macromolecular complex. Described are the acclimatization responses in the light-harvesting system of the cyanobacterium Anacystis nidulans following a shift from high intensity, white light to low intensity, red light.

The phycocyanin and chlorophyll content and the relative amount of the two linker peptides (33 and 30 kilodaltons) in the phycobilisome were studied. Both the phycocyanin and chlorophyll content per cell increased after the shift, although the phycocyanin increased relatively more. The increase in phycocyanin was biphasic in nature, a fast initial phase and a slower second phase, while the chlorophyll increase was completed in one phase. The phycocyanin and chlorophyll responses to red light were immediate and were completed within 30 and 80 hours for chlorophyll and phycocyanin, respectively. An immediate response was also seen for the two phycobilisome linker peptides. The amount of both of them increased after the shift, although the 33 kilodalton linker peptide increased faster than the 30 kilodalton linker peptide. The increase of the content of the two linker peptides stopped when the phycocyanin increase shifted from the first to the second phase. We believe that the first phase of phycocyanin increase was due mainly to an increase in the phycobilisome size while the second phase was caused only by an increase in the amount of phycobilisomes. The termination of chlorophyll accumulation, which indicates that no further reaction center chlorophyll antennae were formed, occurred parallel to the onset of the second phase of phycocyanin accumulation.

     

EFFECT OF LIGHT INTENSITY AND GLYCEROL ON THE GROWTH,PIGMENT COMPOSITION,AND ULTRASTRUCTURE OF CHROOMONAS SP.1,2,3

Growth of Chroomonas sp. increased with light intensity (100, 1800, and 2700 μW/cm²) with a fivefold increase from the lowest to the highest intensity. Chlorophyll and phycocyanin content per cell were greater in cells grown at low light intensity, but the ratio of chlorophyll a and c did not vary appreciably. Cells grown at low light intensity had 30% more phycocyanin than cells grown at high intensities of light. The chloroplast of cells with the higher phycocyanin content had average intrathyla-koidal widths of 300 Å, whereas those cells with the lower phycocyanin content had average intrathylakoidal widths of 200 Å. This result is compatible with the hypothesis that phycocyanin is located in the intrathylakoidal space in the cryptophyte algae. Of the various energy sources tested, only glycerol was able to support limited growth tinder nonphotosynthetic conditions. Under no condition was the chloroplast reduced to an elioplast or proplastid state. Starch accumulation was greatest in cells grown in continuous while light in glycerol. Eye-spots were commonest in cells grown in darkness and interrupted every 24 hr by a few seconds of white light. It was concluded that this organism is an obligate phototroph.     

Chlorosis during nitrogen starvation is altered by carbon dioxide and temperature status and is mediated by the ClpP1 protease in <Emphasis Type="Italic">Synechococcus elongatus</Emphasis>

The interactive effects of inorganic carbon status, temperature and light on chlorosis induced by nitrogen deficiency, and the roles of Clp proteases in this process were investigated. In wild-type cultures grown in high or ambient CO₂, following transfer to media lacking combined nitrogen, phycocyanin per cell dropped primarily through dilution of the pigment through cell division, and also suffered variable degrees of net degradation. When grown at high CO₂ (5%), chlorophyll (Chl) suffered net degradation to a greater extent than phycocyanin. In marked contrast, growth at ambient CO₂ resulted in Chl per cell dropping through dilution. Conditions that drove net Chl degradation in the wild-type resulted in little or no net Chl degradation in a clpPI inactivation mutant, with Chl content dropping largely through growth dilution in the mutant. The chlorotic response of a clpPII inactivation strain was nearly the same as that of wild-type, although phycocyanin degradation may have been slightly accelerated in the former.     

Variations in biochemical parameters of Heterocapsa sp. and Olisthodiscus luteus grown in 12:12 light:dark cycles II. Changes in pigment composition

Photosynthetic pigment composition was studied in batch cultures of Heterocapsa sp. and Olisthodiscus luteus growing exponentially in a 12:12 light:dark cycle. Both species divided in the dark. The synthesis of pigments was continuous for both species. However for chlorophyll c and peridinin, in Heterocapsa sp., and chlorophyll c and fucoxanthin, in O. luteus, (pigments belonging to light harvesting complexes) the synthesis was significantly higher during the light period. Concentrations per total cell volume (TCV) of chlorophyll a, chlorophyll c, peridinin and diadinoxanthin in Heterocapsa sp., and chlorophyll a, chlorophyll c, fucoxanthin and violaxanthin in O. luteus, showed a maximum at the onset of light and decreased during the light period. The values of the chlorophyll a:chlorophyll c, chlorophyll a:peridinin and chlorophyll a:fucoxanthin ratios are compared with data reported in the literature.     

Functional organization and plasticity of the photosynthetic unit of the cyanobacterium Anacystis nidulans

Anacystis nidulans grown under high and low light, 100 and 10 μE m^?2 s^?1, respectively, was analyzed with respect to chlorophyll/P700, phycobiliproteins/P700, chlorophyll/cell, and oxygen evolution parameters. The photosynthetic unit sizes of this cyanobacterium, measured as the ratio of total chromophores (chlorophyll and bilin) to P700, were shown to be similar to those of higher plants and green algae. High light grown cells possessed a photosynthetic unit consisting of a core of 157 ± 6 chlorophyll a molecules per P700 associated with a light harvesting system of 95 ± 3.5 biliprotein chromophores. Low light grown cells had substantially more biliprotein chromophores per P700 (125 ± 3.1) than high light cells, but showed no significant difference in the numbers of chlorophyll a molecules per P700 (149 ± 4). Analyses of aqueous biliprotein extracts indicate that low light grown cells produce proportionately more phycocyanin relative to allophycocyanin than high light cells. Calculations of the molecular weight of biliproteins per P700 suggest that there is less than one phycobilisome per reaction center I under both growth conditions. Differences in chlorophyll/cell ratios and oxygen evolution characteristics were also observed. High light cells contain 6.3 × 10^?12 mg chlorophyll cell^?1, while low light grown cells contain 12.8 × 10^?12 mg chlorophyll cell^?1. Photosynthetic oxygen evolution rate vs. light intensity curves indicate that high light grown cells reach maximal levels of oxygen evolution at higher light intensity than low light grown cells. Maximal rates of oxygen evolution were 16.6 μmol oxygen min^?1 (mg chlorophyll)^?1 for high and 8.4 μmol oxygen min^?1 (mg chlorophyll)^?1 for low light cells. Maximal oxygen evolution rates per cell were equivalent for both cell types, although the amount of P700 per cell was lower in high light cells. High light grown cells are therefore capable of producing more oxygen per reaction center I than low light grown cells.     

Energy Transfer from the Phycobilisomes to Photosystem II Reaction Centers in Wild Type Cyanidium caldarium

Nonsaturating light at 600 or 436 nanometers was used to excite specifically phycocyanin or chlorophyll a, respectively, both of which participate in light capture in photosystem II of Cyanidium caldarium. The ratio of absorption of light by phycocyanin to chlorophyll in photosystem II in this organism is >20 at 600 nanometers and ≤0.2 at 436 nanometers.     

Internal conversion in the photosynthetic mechanism of blue-green algae

1. In Chroococcus a quantum of light absorbed by phycocyanin has 90 per cent the chance of doing photosynthesis that a quantum absorbed by chlorophyll has. 2. By a process analogous to internal conversion in radioactivity (but with the linear dimensions and the wave length 10⁴ times larger) there will be transferred from phycocyanin to chlorophyll See PDF for Equation (a number of the order of 100) quanta for every one emitted as fluorescent light by the phycocyanin in the Chroococcus cell. 3. The yield of fluorescent light in Chroococcus is between 1 and 2 per cent. 4. The transfer of energy by internal conversion can account for the photosynthesis by phycocyanin observed by Emerson and Lewis.     

Untersuchung der Beziehung zwischen Pigmentzusammensetzung und CO2-Gaswechsel bei der Blaualge Anacystis nidulans

Summary Changes in culture conditions caused strong changes in the pigment composition in the blue-green alga Anacystis nidulans. Under normal illumination (white light; 0.6·10³ erg/cm²·sec) the relation between the amounts of chlorophyll a and phycocyanin was 1:6.6. In a high light intensity (20.8·10³ erg/cm²·sec) the phycocyanin content was reduced and the relations thus changed to 1:1.9. Growing the algae in red light of high intensity (20·10³ erg/cm²·sec) increased the phycocyanin content; the chlorophyll a: phycocyanin relation was then 1:12.1.The action spectrum of apparent photosynthesis showed a minimum at 473 nm in all three cultures. The maximum of photosynthesis in low light cultures fell in the absorption region of phycocyanin at 621 nm. The action spectrum of the red light culture showed a reduced rate of photosynthesis in the same region. The strong light culture had an action spectrum similar to that of the red light culture with a maximum at 651 nm. The differing action spectrum of the low light culture may be a result of interruption in the energy transfer from phycocyanin to chlorophyll a within pigment system II.The transients of CO₂ exchange are independent of the pigment composition. Two different types of transients were found depending on the wavelength of the incident light. In red light of 550–650 nm a higher stationary rate was reached after a maximum of photosynthesis at the beginning of the illumination period. In blue and far red light a lower rate was found after the first maximum. Following a illumination period in blue or far red light a CO₂ evolution in the dark was observed. On the other hand, this CO₂ evolution was not found after illumination with red light. These effects are possiblt caused by a decarboxylation reaction (photorespiration) which occurs only in blue and far red light.     

CYCLING OF STOMATAL APERTURE IN LEAVES OF PLANTS WITH CRASSULACEAN ACID METABOLISM UNDER CONSTANT CONDITIONS

When leaves of plants with C₃ metabolism are detached and held in darkness, they senesce and the stomata close. Because the relation of senescence and stomatal closure is very close, if not actually causal, the question arose as to whether in the leaves of plants with Crassulacean acid metabolism whose stomata open at night the relationship to senescence would be reversed. Detached leaves of four species of Hoya, floated on water in constant darkness or constant light, were found to show no large differences in stomatal aperture (measured as diffusion resistance) between those in the light or dark, but the aperture changed in a regular circadian rhythm. In some leaves the rhythm was simple, in others the peak showed small secondary peaks, but in all cases the values were nearly the same in the light as in the dark, throughout the cycle. Previous culture of the intact plants under normal day/night conditions gave results similar to those with plants that had had prolonged culture under constant light or darkness. In those cases when the stomata were more open in the dark, the chlorophyll content was greater than when the stomata were more open in the light; but when they were more open in the light, the chlorophyll content showed little difference between light and dark. When the leaves had only their petioles in water they showed greater senescence in the light than in the dark, and the stomata were more tightly closed in the light, especially at the apical ends. All four species of Hoya gave similar results. We deduce that senescence of these leaves is modified by stomatal aperture, and generally in the same direction as in C₃ leaves, but that in continuous light or darkness the primary control over the aperture is the endogenous cycle.     

Multiple actions of abscisic acid in senescence of oat leaves

The modifications induced by abscisic acid (ABA) on the senescence of oat leaves in darkness have been studied and are compared with its well-known effects in light. Contrary to the action in light, ABA preserves chlorophyll (Chl) in the dark almost as well as kinetin. Chlorophylla is decolorized more extensively thanb, and the content ofb is maintained by ABA almost at its initial level for 4 days. ABA also prevents proteolysis in darkness just as completely as chlorophyll loss, the relationship of both breakdown processes to ABA concentration being strictly log-linear over the range from 1 to 100 M. In line with this action, ABA inhibits formation of the neutral protease in the dark but not in the light. The data suggest that ABA and kinetin operate to preserve chlorophyll and protein by different mechanisms, since their actions are neither independent nor synergistic but actually interfere with one another. In this connection, protein values given by the Lowry and Bradford methods have been compared. In parallel with the effect on senescence, ABA slowly opens the stomata in the dark. This effect increases with time, and by day 3 the stomata in ABA are as open as in leaves on water in light. Thus all these effects of ABA in darkness are strikingly opposite to those commonly observed on leaves in natural lighting. In addition, ABA powerfully inhibits the formation of ethylene in the dark by the detached oat leaves, and this inhibition also tends to increase with time. Finally, a slight antagonism to ABA's action on senescence is exerted byp-coumaric acid in the light but not in the dark.     

Changes in pigment content of the diatom Navicula pelliculosa (Bréb.) Hilse in silicon-starvation synchrony

Summary Exponentially grown cells of the freshwater diatom Navicula pelliculosa (Bréb) Hilse, contained chlorophyll a, chlorophyll c, fucoxanthin, diadinoxanthin, diatoxanthin, neofucoxanthin, -carotene, and an unknown pigment, the absorption spectrum of which is reported. Changes in amounts of chlorophyll a, fucoxanthin and diadinoxanthin were determined during the course of silicon-starvation synchrony carried out in the light or dark. Changes in the rate of chlorophyll a and fucoxanthin syntheses were similar. Synthesis ceased after 5–7 hr of silicon starvation, but recommenced in cultures kept in the light, once silicon was re-introduced. In cultures kept in the dark no significant synthesis was observed after re-introduction of silicon. Diadinoxanthin synthesis continued in the light at all times, although at a lower rate during the silicon-starvation period. In the dark, synthesis of this pigment ceased when cell division stopped, and the amount per unit volume of culture decreased. These results are discussed in relation both to the effect of silicon on the metabolism of the diatom and to the possible function of the carotenoids.Dedicated to Prof. C. B. van Niel on the occasion of his 70th birthday.     

Fluorescence in blue light (FLU) is involved in inactivation and localization of glutamyl‐tRNA reductase during light exposure

Fluorescent in blue light (FLU) is a negative regulator involved in dark repression of 5‐aminolevulinic acid (ALA) synthesis and interacts with glutamyl‐tRNA reductase (GluTR), the rate‐limiting enzyme of tetrapyrrole biosynthesis. In this study, we investigated FLU‘s regulatory function in light‐exposed FLU‐overexpressing (FLUOE) Arabidopsis lines and under fluctuating light intensities in wild‐type (WT) and flu seedlings. FLUOE lines suppress ALA synthesis in the light, resulting in reduced chlorophyll content, but more strongly in low and high light than in medium growth light. This situation indicates that FLU's impact on chlorophyll biosynthesis depends on light intensity. FLU overexpressors contain strongly increased amounts of mainly membrane‐associated GluTR. These findings correlate with FLU‐dependent localization of GluTR to plastidic membranes and concomitant inhibition, such that only the soluble GluTR fraction is active. The overaccumulation of membrane‐associated GluTR indicates that FLU binding enhances GluTR stability. Interestingly, under fluctuating light, the leaves of flu mutants contain less chlorophyll compared with WT and become necrotic. We propose that FLU is basically required for fine‐tuned ALA synthesis. FLU not only mediates dark repression of ALA synthesis, but functions also to control balanced ALA synthesis under variable light intensities to ensure the adequate supply of chlorophyll.     

PLASTID FUNCTION IN PLANT TISSUE CULTURES. I. PORPHYRIN SYNTHESIS BY DARK-GROWN HAPLOID AND DIPLOID ALBINO CULTURES

Tissue cultures lacking chlorophyll formed porphyrins when fed δ-aminolevulinic acid, a precursor of tetrapyrroles. When grown in the dark tissues from Ginkgo biloba L., Taxus, and Rosa formed protoporphyrin and several unidentified compounds. When grown in the light cultures did not form these pigments. The protoporphyrin was detected in the tissues after 3–6 hours incubation with δ-aminolevulinic acid; it was localized in the plastids by ultraviolet light microscopy and was identified by extraction procedures, chromatography, and absorption spectroscopy. No magnesium protoporphyrins were found, suggesting that chlorophyll synthesis was blocked at this point. Both male and female haploid albino tissues from Ginkgo formed protoporphyrin. The female albino tissue was derived from a chlorophyll-containing tissue culture from the female gametophyte by serially subculturing the green tissue in the dark. Upon exposing the female albino tissue to light, no greening occurred. The treatments used thus far have not caused chloroplasts to develop in the haploid albino tissues, even though the tissues contain many amyloplasts. Concurrent with the loss of chloroplasts, the female tissue loses all capacity to differentiate specialized cells, such as tracheids, resin cells, and chlorenchyma.