Characterization of a Synechococcus sp. strain PCC 7002 mutant lacking Photosystem I. Protein assembly and energy distribution in the absence of the Photosystem I reaction center core complex

A Synechococcus sp. strain PCC 7002 psaAB::cat mutant has been constructed by deletional interposon mutagenesis of the psaA and psaB genes through selection and segregation under low-light conditions. This strain can grow photoheterotrophically with glycerol as carbon source with a doubling time of 25 h at low light intensity (10 E m^–2 s^–1). No Photosystem I (PS I)-associated chlorophyll fluorescence emission peak was detected in the psaAB::cat mutant. The chlorophyll content of the psaAB::cat mutant was approximately 20% that of the wild-type strain on a per cell basis. In the absence of the PsaA and PsaB proteins, several other PS I proteins do not accumulate to normal levels. Assembly of the peripheral PS I proteins PsaC,PsaD, PsaE, and PsaL is dependent on the presence of the PsaA and PsaB heterodimer core. The precursor form of PsaF may be inserted into the thylakoid membrane but is not processed to its mature form in the absence of PsaA and PsaB. The absence of PS I reaction centers has no apparent effect on Photosystem II (PS II) assembly and activity. Although the mutant exhibited somewhat greater fluorescence emission from phycocyanin, most of the light energy absorbed by phycobilisomes was efficiently transferred to the PS II reaction centers in the absence of the PS I. No light state transition could be detected in the psaAB::cat strain; in the absence of PS I, cells remain in state 1. Development of this relatively light-tolerant strain lacking PS I provides an important new tool for the genetic manipulation of PS I and further demonstrates the utility of Synechococcus sp. PCC 7002 for structural and functional analyses of the PS I reaction center.Abbreviations ATCC American type culture collection - Chl chlorophyll - DCMU 3-(3,4-dichlorophyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - HEPES N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid] - PCC Pasteur culture collection - PS I Photosystem I - PS II Photosystem II - SDS sodium dodecyl sulfate     

The consequences of chlorophyll deficiency for photosynthetic light use efficiency in a single nuclear gene mutation of cowpea

The light harvesting and photosynthetic characteristics of a chlorophyll-deficient mutant of cowpea (Vigna unguilata), resulting from a single nuclear gene mutation, are examined. The 40% reduction in total chlorophyll content per leaf area in the mutant is associated with a 55% reduction in pigment-proteins of the light harvesting complex associated with Photosystem II (LHC II), and to a lesser extent (35%) in the light harvesting complex associated with Photosystem I (LHC I). No significant differences were found in the Photosystem I (PS I) and Photosystem II (PS II) contents per leaf area of the mutant compared to the wildtype parent. The decreases in the PS I and PS II antennae sizes in the mutant were not accompanied by any major changes in quantum efficiencies of PS I and PS II in leaves at non-saturating light levels for CO₂ assimilation. Although the chlorophyll deficiency resulted in an 11% decrease in light absorption by mutant leaves, their maximum quantum yield and light saturated rate of CO₂ assimilation were similar to those of wildtype leaves. Consequently, the large and different decreases in the antennae of PS II and PS I in the mutant are not associated with any loss of light use efficiency in photosynthesis.Abbreviations LHC I, LHC II light harvesting chlorophyll a/b protein complexes associated with PS I and PS II - A₈₂₀ light-induced absorbance change at 820 nm - ø_{PS I}, ø_{PS II} relative quantum efficiencies of PS I and PS II photochemistry     

Detection of point mutations in chloroplast genes of Antirrhinum majus L. I. Identification of a point mutation in the psaB gene of a photosystem I plastome mutant

A point mutation in the plastome-encoded psaB gene of the mutant en:alba-1 of Antirrhinum majus L. was identified by an analysis of chloroplast DNA with a modified PCR-SSCP technique. Application of this technique is indicated when a gene or a group of genes is known in which the point mutation is located. Analysis of primary photosynthetic reactions in the yellowish white plastome mutant indicated a dysfunction of photosystem (PS) 1. The peak wavelength of PS I-dependent chlorophyll (Chl) fluorescence emission at 77 K was shifted by 4 nm to 730 nm, as compared to fluorescence from wild-type. There were no redox transients of the reaction center Chl P₇₀₀ upon illumination of leaves with continuous far-red light or with rate-saturating flashes of white light. The PS I reaction center proteins PsaA and PsaB are not detectable by SDS-PAGE in mutant plastids. Hence, plastome encoded PS I genes were regarded as putative sites of mutation. In order to identify plastome mutations we developed a modified SSCP (single-strand conformation polymorphism) procedure using a large PCR fragment which can be cleaved with various restriction enzymes. When DNA from wild-type and en:alba-1 was submitted to SSCP analysis, a single stranded Hinf I fragment of a PCR product of the psaB gene showed differences in electrophoretic mobility. Sequence analysis revealed that the observed SSCP was caused by a single base substitution at codon 136 (TAT TAG) of the psaB gene. The point mutation produces a new stop codon that leads to a truncated PsaB protein. The results presented indicate that the mutation prevents the assembly of a functional PS I complex. The applicability to other plastome mutants of the new method for detection of point mutations is discussed.     

Competition between annihilation and trapping leads to strongly reduced yields of photochemistry under ps-flash excitation

Excitation of photosynthetic systems with short intense flashes is known to lead to exciton-exciton annihilation processes. Here we quantify the effect of competition between annihilation and trapping for Photosystem II, Photosystem I (thylakoids from peas and membranes from the cyanobacterium Synechocystis sp.), as well as for the purple bacterium Rhodospirillum rubrum. In none of the cases it was possible to reach complete product saturation (i.e. closure of reaction centers) even with an excitation energy exceeding 10 hits per photosynthetic unit. The parameter introduced by Deprez et al. ((1990) Biochim. Biophys. Acta 1015: 295–303) describing the competition between exciton-exciton annihilation and trapping was calculated to range between 4.5 (PS II) and 6 (Rs. rubrum). The rate constants for bimolecular exciton-exciton annihilation ranged between (42 ps)^-1 and (2.5 ps)^-1 for PS II and PS I-membranes of Synechocystis, respectively. The data are interpreted in terms of hopping times (i.e. mean residence time of the excited state on a chromophore) according to random walk in isoenergetic antenna.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - LHC II light harvesting complex II - P primary donor - PS I Photosystem I - PS II Photosystem II - PSU photosynthetic unit - RC reaction center     

Observations on the photohydrogen producing activity during the synchronous cell cycle of Scenedesmus obliquus

In anaerobically adapted samples of synchronized cultures of the unicellular green alga Scenedesmus obliquus it was observed that both the rate and the maximum volume of hydrogen produced in the light changed in a parallel fashion over the life cycle. These two parameters of cells of the 16th h were 3 times greater than the comparable values for cells of the 8th h. Although both photosystems are involved in photohydrogen production the patterns seen over a complete life cycle (24 h) for hydrogen metabolism was inverse to that noted for changes in the photosynthetic capacity. The provision of either glucose, ethanol or acetate to 8th and 16th h cultures enhanced photohydrogen production of the 8th to the same level as the 16th h. From these findings, and also from the observation that the starch content is low at the 8th but 4 fold at the 16th h, it is apparent that in autotrophic cultures an endogenous organic compound, and not water, serves as the electron donor for photohydrogen production. Since free glucose was not detected the natural substrate is most likely starch. From experiments with monochromatic light and observations on the inhibitory action of DCMU and DBMIB on photohydrogen production we conclude that the major portion of the machinery for photohydrogen production in Scenedesmus requires both PS I and PS II participation and the input of electrons from the natural substrate proceeds through PS II.The alternate possibility that glucose, acetate and ethanol also act as inhibitors of reactions, most probably photophosphorylation, which compete with photohydrogen production was suggested by some experiments. The subsequent modulation of hydrogenase activity was discussed as a possible reason for the enhancement of photohydrogen production.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - Chl chlorophyll - DCMU 3-(3, 4-dichlorophenyl)-1,1-dimethyl-urea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - NAD nicotinamide adenine dinucleotide - PSI photosystem I - PSII photosystem II - PCV packed cell volume     

Decrease of polypeptides in the PS I antenna complex with increasing growth irradiance in the red alga Porphyridium cruentum

Thylakoids isolated from cells of the red alga Porphyridium cruentum exhibit an increased PS I activity on a chlorophyll basis with increasing growth irradiance, even though the stoichiometry of Photosystems I and II in such cells shows little change (Cunningham et al. (1989) Plant Physiol 91: 1179–1187). PS I activity was 26% greater in thylakoids of cells acclimated at 280 mol photons · m^–2 · s^–1 (VHL) than in cells acclimated at 10 mol photons · m^–2 · s^–1 (LL), indicating a change in the light absorbance capacity of PS I. Upon isolating PS I holocomplexes from VHL cells it was found that they contained 132±9 Chl/P700 while those obtained from LL cells had 165±4 Chl/P700. Examination of the polypeptide composition of PS I holocomplexes on SDS-PAGE showed a notable decrease of three polypeptides (19.5, 21.0 and 22 kDa) in VHL-complexes relative to LL-complexes. These polypeptides belong to a novel LHC I complex, recently discovered in red algae (Wolfe et al. (1994a) Nature 367: 566–568), that lacks Chl b and includes at least six different polypeptides. We suggest that the decrease in PS I Chl antenna size observed with increasing irradiance is attributable to changes occurring in the LHC I-antenna complex. Evidence for a Chl-binding antenna complex associated with PS II core complexes is lacking at this point. LHC II-type polypeptides were not observed in functionally active PS II preparations (Wolfe et al. (1994b) Biochimica Biophysica Acta 1188: 357–366), nor did we detect polypeptides that showed immunocross-reactivity with LHC II specific antisera (made to Chlamydomonas and Euglena LHC II).Abbreviations Bis-Tris bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane - DCPIP 2,6-dichlorophenol indophenol - -dm dodecyl--d-maltoside - HL high light of 150 mol photons · m^–2 · s^–1 - LGB lower green band - LHC I light-harvesting complex of PS I - LHC II light-harvesting complex of PS II - LL low light of 10 mol photons · m^–2 · s^–1 - ML medium light of 50 mol photons · m^–2 · s^–1 - MES 2-(N-morpholino) ethanesulfonic acid - P700 reaction center of PS I - PFD photon flux density - Trizma tris(hydroxymethyl)aminomethane - UGB upper green band - VHL very high light of 280 mol photons · m^–2 · s^–1     

Leaf senescence in a non-yellowing mutant of Festuca pratensis: Photosynthesis and photosynthetic electron transport

The photosynthetic capacity of detached leaves of a non-yellowing mutant of Festuca pratensis Huds. declined during senescence at a similar rate to that in a normal cultivar. Respiratory oxygen uptake in the dark continued at similar rates in both genotypes during several days of senescence. In chloroplasts isolated from leaves at intervals after excision, the rate of photosystem I (PS I)-mediated methyl viologen reduction using reduced N,N,N,N-tetramethyl-p-phenylene diamine as electron donor also declined in both genotypes, possibly due to loss of integrity of the photosynthetic apparatus in the cytochrome f-plastocyanin region. There was a similar fall in PS II electron transport using water as electron donor and measured at the rate of reduction of 2,6-dichlorophenolindophenol. Partial restoration of this activity by the addition of diphenyl carbazide was evidence for lability of the oxygen-evolving complex during senescence. An accentuated difference between mutant and normal material in this case indicated that the mutant retains a greater number of functional PS II centres. Changes in the light-saturation characteristics of the two photosystems have been discussed in relation to the organization of the photosynthetic membranes during senescence.Abbreviations and symbols DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolindophenol - DMSO dimethyl sulphoxide - DPC diphenyl carbazide - MV methyl viologen - PS I, PS II photosystem I, II - TMPD N,N,N,N-tetramethyl-p-phenylene diamine     

Light-harvesting pigment-protein complex deficiency in Hosta (Liliaceae)

A yellow-leaved plastome mutant of Hosta (Hosta sieboldii Ingram complex, Liliaceae) known as Wogan Gold lacks normal granal stacks, but has numerous stroma lamellae extending throughout the chloroplast. The chlorophyll a/b ratio is 0.76 in the mutant and 2.9 in wild type. The mutant contains a qualitatively normal pattern of other photosynthetic co-pigments. SDS-polyacrylamide gel electrophoresis showed a deficiency in the photosystem (PS) II light-harvesting complex. Since PS II is localized mainly in the granal region, the absence of the light-harvesting complex may explain the loss of granal stacking in this mutant.Abbreviation PS photosystem     

Thylakoid membrane energization and swelling in photoinhibited Chlamydomonas cells is prevented in mutants unable to perform cyclic electron flow

Photoinhibition of Photosystem II in unicellular algae in vivo is accompanied by thylakoid membrane energization and generation of a relatively high pH as demonstrated by ¹⁴C-methylamine uptake in intact cells. Presence of ammonium ions in the medium causes extensive swelling of the thylakoid membranes in photoinhibited Chlamydomonas reinhardtii but not in Scenedesmus obliquus wild type and LF-1 mutant cells. The rise in pH and the related thylakoid swelling do not occur at light intensities which do not induce photoinhibition. The rise in pH and membrane energization are not induced by photoinhibitory light in C. reinhardtii mutant cells possessing an active Photosystem II but lacking cytochrome b₆/f, plastocyanin or Photosystem I activity and thus being unable to perform cyclic electron flow around Photosystem I. In these mutants the light-induced turnover of the D1 protein of Reaction Center II is considerably reduced. The high light-dependent rise in pH is induced in the LF-1 mutant of Scenedesmus which can not oxidize water but otherwise possesses an active Reaction Center II indicating that PS II-linear electron flow activity and reduction of plastoquinone are not required for this process. Based on these results we conclude that photoinhibition of Photosystem II activates cyclic electron flow around Photosystem I which is responsible for the high membrane energization and pH rise in cells exposed to excessive light intensities.Abbreviations cyt b₆/f cytochrome b₆/f - Diuron 3-(3,4-dichlorophenyl)-1 dimethyl urea - Q_B the secondary quinone acceptor of reaction center II - DNP 2,4,Dinitrophenol - FCCP carbonyl cyanide trifluoromethoxy phenylhydrazone - SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis     

Consequences of LHC II deficiency for photosynthetic regulation in chlorina mutants of barley

The light-harvesting chlorophyll a/b proteins associated with PS II (LHC II) are often considered to have a regulatory role in photosynthesis. The photosynthetic responses of four chlorina mutants of barley, which are deficient in LHC II to varying degrees, are examined to evaluate whether LHC II plays a regulatory role in photosynthesis. The efficiencies of light use for PS I and PS II photochemistry and for CO₂ assimilation in leaves of the mutants were monitored simultaneously over a wide range of photon flux densities of white light in the presence and absence of supplementary red light. It is demonstrated that the depletions of LHC II in these mutants results in a severe imbalance in the relative rates of excitation of PS I and PS II in favour of PS I, which cannot be alleviated by preferential excitation of PS II. Analyses of xanthophyll cycle pigments and fluorescence quenching in leaves of the mutants indicated that the major LHC II components are not required to facilitate the light-induced quenching associated with zeaxanthin formation. It is concluded that LHC II is important to balance the distribution of excitation energy between PS I and PS II populations over a wide range of photon flux densities. It appears that LHC II may also be important in determining the quantum efficiency of PS II photochemistry by reducing the rate of quenching of excitation energy in the PS II primary antennae.Abbreviations Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_p photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - ø_PSI, ø_PSII relative quantum efficiencies of PS I and PS II photochemistry - øCO₂ quantum yield of CO₂ assimilation     

Cloning and sequencing of the hemA gene of Rhodobacter capsulatus and isolation of a δ-aminolevulinic acid-dependent mutant strain

Summary The Rhodobacter capsulatus hemA gene, coding for the enzyme -aminolevulinic acid synthase (ALAS), was isolated from a genome bank by hybridization with a hemT probe from Rhodobacter sphaeroides. Subcloning of the initial 3.9 kb HindIII fragment allowed the isolation of a 2.5 kb HindIII-BglII fragment which was able to complement the -aminolevulinic acid-requiring (ALA-requiring) Escherichia coli mutant SHSP19. DNA sequencing revealed an open reading frame coding for a protein with 401 amino acids which displayed similarity to the amino acid sequences of other known ALASs. However, no resemblance was seen to the HemA protein of E. coli K12. Based on the sequence data, an ALA-requiring mutant strain of R. capsulatus was constructed by site-directed insertion mutagenesis. Introduction of a plasmid, containing the hemA gene of R. capsulatus on the 3.9 kb HindIII fragment, restored ALA-independent growth of the mutant indicating that there is only one gene for ALA biosynthesis in R. capsulatus. Transfer of the R factor pRPS404 and hybridization analysis revealed that the ALAS gene is not located within the major photosynthetic gene cluster.Part of this research was presented at the Symposium on Molecular Biology of Membrane-Bound Complexes in Phototrophic Bacteria, Freiburg, FRG, 2–5 August 1989     

Photochemical activities,pigment distribution and photosynthetic unit size of subchloroplast particles isolated from synchronized cells of Scenedesmus obliquus

Photosystem II (PS II) reactions of chloroplast particles show the same variations during the synchronous life cycle of Scenedesmus obliquus, strain D₃ (Gaffron Biol. Zbl. 59, 302 1939), as the whole cells they derived from. Photosystem I (PS I) reactions of whole cells and of subchloroplast particles show little or no variation in their activity, whereas PS I reactions of chloroplast particles vary like PS II reactions during the life cycle. The variation in chloroplast particles could be attributed to the change in the reoxidation capacity of plastoquinone still attached to PS I. Digitonin-treatment of chloroplast particles from Scenedesmus and subsequent sucrose density gradient separation yielded 3 distinct fractions: Fraction I contained pure PS I particles with the most efficient PS I-mediated methylviologen (MV) reduction with subsequent oxygen uptake (3 mmol O₂/mg Chl·h); no Hill reaction; and a high chlorophyll a/b ratio, and a vast amount of unbound protein xanthophyll complexes. Fraction II is enriched in PS II particles, with little PS I activity (less than 10% of the PS I particles) and a low chlorophyll a/b ratio. The activity of the water-splitting system was completely lost. This fraction must also contain most of the light-harvesting pigment system. Fraction III is also enriched in PS II with even less PS I activity, but the ratio of chlorophyll a/b is slightly higher than in whole cells and the water-splitting system is intact. -carotene was part of all fractions whereas functional xanthophylls seemed to be restricted to the PS II particles. From the constant chlorophyll P/700 ratio we had to conclude that size of the photosynthetic unit does not change during the life cycle of a synchronized Scenedesmus obliquus culture.Abbreviations DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea - DCPIP dichlorphenolindophenol - MV methylviologen (paraquat) - PS I photosystem I - PS II photosystem II - DPC diphenyl-carbazide     

Optimized production of L-β-hydroxybutyric acid by a mutant of Yarrowia lipolytica

A mutant strain of Yarrowia lipolytica was developed which produced 8.0 g l--hydroxybutyric acid l^–1 from butyric acid in a batch culture. The optimum culture conditions in the fermenter for maintenance of a high cell activity, determined by chemostat analyses, were a specific growth rate of 0.06 h^–1, a glucose concentration of 2.0 g l^–1, and a butyric acid concentration of 8.1 g l^–1. A fed-batch fermentation was performed under these conditions resulting in an l--hydroxybutyric acid yield of 31 g l^–1.     

Photosynthetic performance and fluorescence in relation to antenna size and absorption cross-sections in rye and barley grown under normal and intermittent light conditions

The size of the Photosystem II light harvesting antenna and the absorption cross-sections of PS I (_PSI) and PS II (_PSII) were examined in relation to photosynthetic performance fluorescence. Wild-type (WT) rye (Secale cereale) and barley (Hordeurn vulgare) as well as the barley chlorophyllb-less chlorina F2 mutant were grown under control and intermittent light (IML) conditions. (_PSII) in control barley F2 was similar to IML grown WT rye and barley, which, in turn was 2.5 to 3.5 times smaller than for control WT plants. In contrast, _PSI was similar for all control plants. This was 2.5 to 4 times larger than for IML-grown WT plants. IML-grown barley mutant plants had the smallest absorption cross-sections. Photosynthetic light response curves revealed that the barley chlorina F2-mutant had rates of oxygen evolution on a per leaf area basis that were only slightly lower than control WT rye and barley while IML-grown plants had strongly reduced photosynthetic performance. Convexity () for control barley chlorina F2-mutants was equal to the WT controls (0.6–0.7), while all IML-grown plants had a of 0. This indicates that, in contrast to control barley mutants, IML-plants were limited by PS II turn-over rates at all irradiances. However, on a per leaf Chl-basis the IML-grown plants exhibited the highest photosynthetic rates. Thus, the comparatively poor photosynthetic rates for IML-grown plants on a per leaf area basis were not due to less efficient photosynthetic reaction centers, but may rather be due to an increased limitation from PS II turn-over and a reduction in the number of reaction centers per leaf area.     

Heat-induced reversible changes in Photosystem 1 absorption cross-section of pea chloroplasts and sub-chloroplast preparations

Reversible changes in the room temperature fluorescence quenching at 685 nm and light scattering level at 577 nm, indicating about 15% of granal unstacking, induced by high temperature treatment (40°C, for 5 min) of pea chloroplasts were shown. Analysis of the low temperature excitation fluorescence spectra of the 735 nm Photosystem 1 (PS 1) band (F735), in the 635–725 nm region, has revealed the involvement of light-harvesting (LHC 2, maxima at 650 and 676 nm) and the proximal Photosystem 2 antenna (maxima 668, 687 nm) in heat-induced enhancement of the PS 1 long wavelength antenna absorption cross-section. It was found that the two PS 1 sub-chloroplast preparations, achieved by the digitonin method, possessed different characteristics of this enhancement. For the heavier fraction (100 000 g) the additional absorption cross-section was formed mostly at the expense of PS 2 antennas (apparently spillover), but for the lighter PS 1 fraction (145 000 g) the changes have indicated an -transfer mechanism, i.e., participation of only LHC 2 in the energy transfer towards PS 1. This may indicate the heterogeneous character of the temperature-induced energy redistribution across the PS 1-containing chloroplast membrane compartments. The model of heat-induced changes in the pigment-protein complex arrangement is discussed in terms of domain organisation of the thylakoid membrane.Abbreviations Chl a/b ratio between chlorophyll a and chlorophyll b concentrations - CP43 and CP47 proximal Photosystem 2 antenna complexes - D1/D2 complex Photosystem 2 reaction centre complex - EDTA ethylenediaminetetraacetic acid - F685 and F696 Photosystem 2 low temperature fluorescence bands - F735 Photosystem 1 low temperature fluorescence band - Fp free pigment band in green gel electrophoresis - LHC 2 light-harvesting chlorophyll a/b complex - LHCP I, II and III light-harvesting bands in green gel electrophoresis - Cp1 and Cpa bands in green gel electrophoresis which are associated with Photosystem 1 and 2 reaction centre complexes with internal antennas - P700 Photosystem 1 reaction centre - PPC pigment-protein complex - PS 1 and Photosystem 1 alpha and Photosystem 1 beta - PS 2 and Photosystem 2 alpha and Photosystem 2 beta - RC reaction centre - SDS-PAGE sodiumdodecylsulphate-polyacrylamide gel electrophoresis - St1-St2 state-1-state-2 transitions     

Effects of dehydration on the electron transport of Chlorella. An in vivo fluorescence study

Chlorella was used to study the effects of dehydration on photosynthetic activities. The use of unicellular green algae assured that the extent of dehydration was uniform throughout the whole cell population during the course of desiccation. Changes in the activities of the cells were monitored by measurements of fluorescence induction kinetics. It was found that inhibition of most of the photosynthetic activities started at a similar level of cellular water content. They included CO₂ fixation, photochemical activity of Photosystem II and electron transport through Photosystem I. The blockage of electron flow through Photosystem I was complete and the whole transition occurred within a relative short time of dehydration. On the other hand, the suppression of Photosystem II activity was incomplete and the transition took a longer time of dehydration. Upon rehydration, the inhibition of Photosystem II activity was fully reversible when samples were in the middle of the transition, but was not thereafter. The electron transport through Photosystem I was also reversible during the transition, but was only partially afterward.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - F_m maximum fluorescence yield - F₀ non-variable fluorescence level emitted when all PS II centers are open - F_v variable part of fluorescence - PS photosystem - Q_A primary quinone acceptor of Photosystem II     

Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves

Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO₂ assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO₂ assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO₂ assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C₃ leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO₂ assimilation.Abbreviations Fm, Fo, Fv maximal, minimal and variable fluorescence yields - Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_P photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - _{PS I}, _{PS II} relative quantum efficiencies of PS I and PS II photochemistry - _{CO 2} quantum yield of CO₂ assimilation     

Simultaneous and selective production of levan and poly(γ-glutamic acid) by <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Bacillus subtilis(natto) Takahashi, used to prepare the fermented soybean product natto, was grown in a basal medium containing 5% (w/w) sucrose and 1.5% (w/w) l-glutamate and produced 58% (w/w) poly(-glutamic acid) and 42% (w/w) levan simultaneously. After 21 h, 40–50 mg levan ml^-1had been produced in medium containing 20% (w/w) sucrose but without l-glutamate. In medium containing l-glutamic acid but without sucrose, mainly poly(-glutamic acid) was produced. Revisions requested 28 August 2004/14 October 2004; Revisions received 11 October 2004/22 November 2004     

Changes in Photosystem II fluorescence in Chlamydomonas reinhardtii exposed to increasing levels of irradiance in relationship to the photosynthetic response to light

The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200 mol m^–2s^–1 on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were investigated using the unicellular green alga Chlamydomonas reinhardtii. It was established that exposure to high light acts at three different regulatory or inhibitory levels; 1) regulation occurs from 300 to 780 mol m^–2s^–1 where total amount of PS II centers and the shape of the light response curve is not significantly changed, 2) a first photoinhibitory range above 780 up to 1600 mol m^–2s^–1 where a progressive inhibition of the quantum yield and the rate of bending (convexity) of the light response curve can be related to the loss of Q_B-reducing centers and 3) a second photoinhibitory range above 1600 mol m^–2s^–1 where the rate of light saturated photosynthesis also decreases and convexity reaches zero. This was related to a particularly large decrease in PS II centers and a large increase in spill-over in energy to PS I.Abbreviations Chl chlorophyll - DCMU 3,(3,4-dichlorophenyl)-1,1-dimethylurea - F_M maximal fluorescence yield - F_pl intermediate fluorescence yield plateau level - F₀ non-variable fluorescence yield - F_v total variable fluorescence yield (F_M-F₀) - initial slope to the light response curve, used as an estimate of initial quantum yield - convexity (rate of bending) of the light response curve of photosynthesis - LHC light-harvesting complex - P_max maximum rate of photosynthesis - PQ plastoquinone - Q photosynthetically active photon flux density (400–700 nm, mol m^–2s^–1) - PS photosystem - Q_A and Q_B primary and secondary quinone electron acceptor of PS II     

Tepidimonas taiwanensis sp. nov., a novel alkaline-protease-producing bacterium isolated from a hot spring

The bacterial strain designated I1-1^T was isolated from a hot spring located in the Pingtung area, southern Taiwan. Cells of this organism were Gram reaction negative rods, motile by a single polar flagellum. Optimum conditions for growth were 55°C and pH 7. Strain I1-1^T grew well in lower nutrient media such as 5–10% Luria–Bertani broth, and its extracellular products expressed alkaline protease activity. The 16S rRNA gene sequence analysis indicates that strain I1-1^T is a member of -Proteobacteria. On the basis of a phylogenetic analysis of 16S rDNA sequences, DNA–DNA similarity data, whole-cell protein analysis, physiological and biochemical characteristics, as well as fatty acid compositions, the organism belonged to the genus Tepidimonas and represented a novel species within this genus. The predominant cellular fatty acids of strain I1-1^T were 16:0 (about 41%), 18:1 7c (about 13%), and summed feature 3 [16:1 7c or 15:0 iso 2OH or both (about 26%)]. Its DNA base ratio was 68.1 mol%. We propose to classify strain I1-1^T (=BCRC 17406^T=LMG 22826^T) as Tepidimonas taiwanensis sp. nov.