Identification of ‘Amigo’ and ‘Kavkaz’ translocations in Ohio soft red winter wheats (Triticum aestivum L.)

One cultivar (GR876) and two advanced Ohio soft red winter wheat lines (OH413 and OH414), with Kavkaz in their pedigrees, were examined for the presence of the Kavkaz, 1RS/1BL rye/wheat chromosome translocation. Another advanced line (OH416), with Amigo in its pedigree, was examined for the presence of the Amigo, 1RS/1AL translocation. Only two satellited chromosomes were observed in most mitotic root-tip cells from GR876, OH413, and OH414, compared to four in most cells from OH416. Heteromorphic bivalents were observed in most PMCs from hybrids produced by crossing GR876, OH413, and OH414 as females to Chinese Spring. No heteromorphic bivalents were observed in PMCs from OH416 x Chinese Spring hybrids. When GR876 and the Ohio lines were hybridized with Chinese Spring dimonotelosomic-1B, telosomic trivalents, consisting of the short- and longarm telosomes paired with chromosome 1B, were only observed in PMCs from 43-chromosome hybrids involving OH416. The long-arm telosome paired with the translocation chromosome, while the short-arm telosome remained unpaired in all other 43-chromosome hybrids. Separation of gliadin proteins from GR876 and the Ohio lines by PAGE revealed that secalin bands for GR876, OH413, and OH414, migrated similarly to the secalins for Kavkaz. Bands for OH416, identified as possible secalins, migrated similarly to those for Amigo. Cultivar GR876 and advanced Ohio soft red winter wheat lines OH413 and OH414 carry the Kavkaz translocation, while OH416 carries the Amigo translocation.Communicated by K. Tsunewaki     

\4 integrin expression onin vitro andin vivo metastatic variants of lewis lung carcinoma

The expression of 4, 6, and 1 integrin subunits has been investigated on somein vitro andin vivo murine metastatic variants derived from Lewis lung carcinoma (3LL). By the use of monoclonal antibodies which recognizes different epitopes of 6, 1, and 4 subunits we demonstrate that 6 and 1 subunits are expressed in all metastatic variants of 3LL irrespective of their metastatic potential, whereas 4 subunit is expressed only in highly metastasizing cells of 3LL. Northern blots of different metastatic variants probed with 1 and 4 subunits demonstrate thata) significant amounts of 1 mRNA were detected in all metastatic variants of 3LL;b) mRNA corresponding to the described entire coding sequence of 4 subunit is expressed only on highly metastasizing cells of 3LL. We conclude that 4 subunit is specifically expressed in highly metastasizig cells of 3LL while is undetectable in lower metastasizing ones.     

The relationship between Photosystem II intrinsic quantum yield and millisecond luminescence in thylakoids

The relationship between charge recombination at Photosystem II (PS II), as indicated by millisecond luminescence, and PS II quantum yield was studied in spinach thylakoids during electron flow to methylviologen. Under the low magnesium conditions used, a decrease in quantum yield was observed in the absence of non-photochemical excitation quenching, and therefore cannot be due to a restriction in excitation delivery to the reaction centre. It was found that the decrease of the parameter _p, which is a measure of the intrinsic quantum yield of open PS II centers, correlates with an increase in luminescence per open center. The relationship between these two parameters was the same whether _p was manipulated by dissipation of the transthylakoid pH gradient or of the electrical potential. This indicates that the mechanism by which _p decreases depends in the same way on the two components of the protonmotive force as does the charge recombination at PS II. Calculation of the yield of luminescence with respect to the back reaction will be necessary to determine whether the charge recombination occurs at a sufficiently high rate to be directly responsible for the _p decrease.     

Mechanisms for controlling balance between light input and utilisation in the salt tolerant alga Dunaliella C9AA

The yield of photosynthetic O₂ evolution was measured in cultures of Dunaliella C9AA over a range of light intensities, and a range of low temperatures at constant light intensity. Changes in the rate of charge separation at Photosystem I (PS I) and Photosystem II (PS II) were estimated by the parameters _{PS I} and _{PS II} . _{PS I} is calculated on the basis of the proportion of centres in the correct redox state for charge separation to occur, as measured spectrophotometrically. _{PS II} is calculated using chlorophyll fluorescence to estimate the proportion of centres in the correct redox state, and also to estimate limitations in excitation delivery to reaction centres. With both increasing light intensity and decreasing temperature it was found that O₂ evolution decreased more than predicted by either _{PS I} or _{PS II}. The results are interpreted as evidence of non-assimilatory electron flow; either linear whole chain, or cyclic around each photosystem.Abbreviations F₀ dark level of chlorophyll fluorescence yield (PS II centres open) - F_m maximum level of chlorophyll fluorescence yield (PS II centres closed) - F_v variable fluorescence (F_m-F₀) - PS I Photosystem I - PS II Photosystem II - P₇₀₀ reaction centre chlorophyll(s) of PS I - q_N coefficient of non-photochemical quenching of chlorophyll fluorescence - q_P coefficient of photochemical quenching of fluorescence yield - q_E high-energy-state quenching coefficient - _{PS I} yield of PS I - _{PS II} yield of PS II - _S yield of photosynthetic O₂ evolution - _P intrinsic yield of open PS II centres     

Functional size of Photosystem II determined by radiation inactivation

The functional size of Photosystem II (PS II) was investigated by radiation inactivation. The technique provides an estimate of the functional mass required for a specific reaction and depends on irradiating samples with high energy -rays and assaying the remaining activity. The analysis is based on target theory that has been modified to take into account the temperature dependence of radiation inactivation of proteins. Using PS II enriched membranes isolated from spinach we determined the functional size of primary charge separation coupled to water oxidation and quinone reduction at the Q_B site: H₂O (Mn)₄ Y_z P680 Pheophytin Q phenyl-p-benzoquinone. Radiation inactivation analysis indicates a functional mass of 88 ± 12 kDa for electron transfer from water to phenyl-p-benzoquinone. It is likely that the reaction center heterodimer polypeptides, D1 and D2, contribute approximately 70 kDa to the functional mass, in which case polypeptides adding up to approximately 20 kDa remain to be identified. Likely candidates are the and subunits of cytochrome b ₅₅₉and the 4.5 kDa psbI gene product.Abbreviations Cyt cytochrome - PS Photosystem - P680 primary electron donor of Photosystem II - Q_A primary quinone acceptor of Photosystem II - Q_B secondary quinone acceptor of Photosystem II - Y_z tyrosine donor to P680     

The appearance of quenching centres in photosystem II

The variable fluorescence quenching found in the presence of DCMU with isolated chloroplasts which have been exposed previously to a prolonged low light intensity (Sinclair and Spence 1988), is accompanied by a loss of the sigmoidal appearance of the fluorescence induction transient. About 80% of the fluorescence decrease is due to the PS II units and 50% of the centres are inactivated by light exposure. Light incubation slows the PS II partial reaction while the PS I partial reaction is unaffected. We propose that in the light, normal PS II centres change into quenching centres which degrade excitation energy to thermal energy. This change can be reversed by 30 min of darkness. A higher flash intensity is needed to saturate the steady state O₂ flash yield from light-incubated chloroplasts indicating a light-induced decrease of the average photosynthetic unit size as would happen if PS II units were preferentially inactivated. These light-induced changes may relate to an adaptation in leaves to increasing light intensity.Abbreviations Chl Chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-Dichlorophenol-Indophenol - EDTA ethylaminediaminetetraacetic acid - F_v Level of variable fluorescence emission - F_o Initial level of fluorescence - Hepes buffer N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]     

Light dependence of quantum yields of Photosystem II and CO2 fixation in C3 and C4 plants

The light dependence of quantum yields of Photosystem II (_II) and of CO₂ fixation were determined in C₃ and C₄ plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO₂ fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=_CO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+R_l)/I_a=_CO2·], where R_L is the rate of respiration in the light. The dependence of the _II/_CO2 and _II/_CO2 ^* ratios on light intensity was then evaluated. In both C₃ and C₄ plants there was little change in the ratio of _II/_CO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of _II/_CO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO₂ fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO₂ fixation under low light intensity may be due to respiratory loss of CO₂. Using dark respiration as an estimate of R_L, the calculated _II/_CO2 ^* ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO₂ fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and _II were made by illuminating upper versus lower leaf surfaces of representative C₃ and C₄ monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of _II/_CO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower _II values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of _II/_CO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO₂ fixation.Abbreviations A measured rate of CO₂ assimilation - A+R_L true rate of CO₂ assimilation; e - CO₂ estimate of electrons transported through PSII per CO₂ fixed by RuBP carboxylase - f fraction of light absorbed by Photosystem II - F'_m yield of PSII chlorophyll fluorescence due to a saturating flash of white light under steady-state photosynthesis - F_s variable yield of fluorescence under steady-state photosynthesis; PPFD-photosynthetic photon flux density - I_a absorbed PPFD - PS II Photosystem II - R_d rate of respiration in the dark - R_I rate of respiration in the light estimated from measurement of R_d or from analysis of quantum yields - apparent quantum yield of CO₂ assimilation under a given condition (A/absorbed PPFD) - true quantum yield of CO₂ assimilation under a given condition [(A+R_L)/(absorbed PPFD)] - quantum yield for photosynthetic O₂ evolution - electrons transported via PS II per quantum absorbed by PS II Supported by USDA Competitive Grant 90-37280-5706.     

Monitoring the mitochondrial transmembrane potential with the JC-1 fluorochrome in programmed cell death during mesophyll leaf senescence

Summary. Analysis of the mitochondrial transmembrane potential (_m) with the help of the JC-1 fluorochrome (5,5,6,6-tetrachloro-1,1,3,3-tetraethylbenzimidazolcarbocyanine iodide) during mesophyll leaf senescence was performed in order to determine whether a reduction of _m takes place during mesophyll senescence and whether plant mitochondria, like mammalian ones, might be involved in the induction of programmed cell death. Fluorescence analysis of mesophyll protoplasts of Pisum sativum in a confocal microscope, fluorescent spectra analysis and time dependence of fluorescence intensity of monomers and of J-aggregates revealed that JC-1 is incorporated and accumulated specifically in plant mitochondria. Analysis of _m during mesophyll protoplast senescence revealed that two subpopulations of mitochondria which differ in _m exist in all analyzed stages of leaf senescence. The first subpopulation contains mitochondria with red fluorescence of J-aggregates due to an unperturbed high _m. The second subpopulation comprises mitochondria with green fluorescence of monomers due to a low _m, proving total depolarization of mitochondrial membranes. Fluorescence analysis demonstrated that even in the latest analyzed stages of leaf senescence, mitochondria with a high _m still exist. Fluorometric measurements revealed that the fluorescence intensity of J-aggregates decreases with the age of plants, which indicates that a reduction of _m during the mesophyll senescence process takes place; however, it does not take place within the whole population of mitochondria of the same protoplast. The reason of this can be due to a dramatic reorganization of mitochondria in mesophyll cells and the appearance of large mitochondria with local heterogeneity of _m in the oldest analyzed stages. All mitochondria in every stage of senescence maintained their membrane organization even when their size, distribution, and spatial organization in protoplasts changed dramatically. We stated that the reduction of _m does not directly induce programmed cell death in mesophyll cells, as opposed to animal apoptosis.Correspondence and reprints: Department of Plant Anatomy and Cytology, Institute of Experimental Biology of Plants, Warsaw University, Miecznikowa 1, 02-096 Warszawa, Poland.     

Characterization of photosystem II in stroma thylakoid membranes

The functional state of the PS II population localized in the stroma exposed non-appressed thylakoid region was investigated by direct analysis of the PS II content of isolated stroma thylakoid vesicles. This PS II population, possessing an antenna size typical for PS II, was found to have a fully functional oxygen evolving capacity in the presence of an added quinone electron acceptor such as phenyl-p-benzoquinone. The sensitivity to DCMU for this PS II population was the same as for PS II in control thylakoids. However, under more physiological conditions, in the absence of an added quinone acceptor, no oxygen was evolved from stroma thylakoid vesicles and their PS II centers were found to be incapable to pass electrons to PS I and to yield NADPH. By comparison of the effect of a variety of added quinone acceptors with different midpoint potentials, it is concluded that the inability of PS II in the stroma thylakoid membranes to contribute to NADPH formation probably is due to that Q_A of this population is not able to reduce PQ, although it can reduce some artificial acceptors like phenyl-p-benzoquinone. These data give further support to the notion of a discrete PS II population in the non-appressed stroma thylakoid region, PS II, having a higher midpoint potential of Q_A than the PS II population in the appressed thylakoid region, PS II. The physiological significance of a PS II population that does not produce any NADPH is discussed.Abbreviations pBQ p-benzoquinone - Chl chlorophyll - DCBQ 2,6-dichloro-p-benzoquinone - DCIP 2,6-dichloroindophenol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DMBQ 2,5-dimethyl-p-benzoquinone - DQ duroquinone(tetramethyl-p-benzoquinone) - FeCN ferricyanide (potassium hexacyanoferrat) - MV methylviologen - NADPH,NADP⁺ reduced or oxidized form of nicotinamide adenine dinucleotide phosphate respectively - PpBQ phenyl-p-benzoquinone - PQ plastoquinone - PS II photosystem II - PS I photosystem I - Q_A primary quinone acceptor of PS II - Q_B secondary quinone acceptor of PS II - E microEinstein     

Compartmentation and flux characteristics of ammonium in spruce

Using ¹³NH ₄ ⁺ as a tracer, compartmental analyses for NH ₄ ⁺ were performed in non-mycorrhizal roots of intact Picea glauca (Moench) Voss. seedlings at four different concentration regimes of external NH ₄ ⁺ ([NH ₄ ⁺ ]_o), i.e. 0, 10, 100, and 1500 M. Three kinetically distinct compartments were identified, with half-lives of exchange of approximately 2 s, 30 s, and 14 min, assumed to represent surface adsorption, Donnan free space, and cytoplasm, respectively. No significant differences were found in half-lives of exchange with changes in [NH ₄ ⁺ ]_o. Influx was calculated to be 0.96 mol·g^–1·h^–1 in N-deprived plants (measured at 10 M [NH ₄ ⁺ ]_o), while under steady-state conditions it was 0.21 mol·g^–1h^–1 at 10 M [NH ₄ ⁺ ]_o, 1.96 mol·g^–1h·^–1 at 100 M [NH ₄ ⁺ ]_o, and 6.45 mol·g^–1·h^–1 at 1.5 mM [NH ₄ ⁺ ]_o. Efflux measured over the same range constituted approximately 9% of influx in N-deprived plants, 10% at 10 M, 28% at 100 M, and 35% at 1.5 mM [NH ₄ ⁺ ]_o. Cytoplasmic [NH ₄ ⁺ ] was estimated at 6 m M in N-deprived plants, 2 mM at 10 M [NH ₄ ⁺ ]_o, 14 mM at 100 M, and 33 mM at 1.5 mM. Free-space [NH ₄ ⁺ ] was 84 M, 50 M, 700 M, and 8 mM, respectively. In comparison with previously published data on fluxes and compartmentation of NO ₃ ^– in white-spruce seedlings, results of this study identify a pronounced physiological preference of this species for NH ₄ ⁺ over NO ₃ ^– as an inorganic N source in terms of uptake and intracellular accumulation. The significant ecological importance of this N-source preference is discussed.The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia campus for providing ¹³N, to Drs. R.D. Guy and S. Silim for providing plant material, and to Dr. M.Y. Wang, Mr. J. Bailey, Mr. J. Mehroke and Mr. P. Poon for essential assistance in experiments.     

Absorbance difference spectra of the S-state transitions in Photosystem II core particles

Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S₀ S₁ S₂ S₃ S₀, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S₃ state with an inactive state, perhaps related to Ca²⁺-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 nm, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the S₁ S₂ transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation. The spectrum of absorbance changes associated with the S₂ S₃ transition was similar to that reported by Lavergne 1991 for PS II membranes. The S₀ S₁ transition was associated with a smaller but still substantial absorbance increase in the UV. Differences with the spectra reported by Lavergne 1991 are attributed to electrostatic effects on electron transfer at the acceptor side associated with the S-state dependence of proton release in PS II membranes.Abbreviations Bis-Tris (bis[2-hydroxyethyl]imino-tris[hydroxymethyl]methane) - DCBQ 2,5-dichloro-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PS II Photosystem II - Q_A secondary electron acceptor of PS II - S₀ to S₄ redox state of the oxygen evolving complex - Z secondary electron donor of PS II     

Synthetic substrate analogues for UDP-GlcNAc: Manα1-6R β(1-2)-N-acetylglucosaminyltransferase II. Substrate specificity and inhibitors for the enzyme

UDP-GlcNAc: Man1-6R (1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man1-6(GlcNAc1-2Man1-3)Man-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in 1-2 linkage to the 2-OH of the Man1-6 residue. The 2-deoxy analogue is a competitive inhibitor (K _i=0.13mm). The 2-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3-, 4- and 6-OH groups are not essential for binding or catalysis since the 3-, 4- and 6-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3-position to pentyl and substituted pentyl groups causes competitive inhibition (K _i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3-O-(4,4-azo)pentyl group and a 3-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man1-6 residue are essential for binding although the 2- and 3-OH face the catalytic site of the enzyme. The 4-OH group of the Man-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Man- substrate analogue. The data are compatible with our previous observations that a bisectingN-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3-OH of the Man1-3 is an essential group for GlcNAc-T II since the 3-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAc1-2Man1-3Man-O-octyl is a good inhibitor (K _i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAc1-2Man1-3Man- arm of the branched substrate to the enzyme is essential for catalysis. Abbreviations: GlcNAc-T I, UDP-GlcNAc:Man1-3R (1-2)-N-acetylglucosaminyltransferase I (EC 2.4.1.101); GlcNAc-T II, UDP-GlcNAc:Man1-6R (1-2)-N-acetylglucosaminyltransferase II (EC 2.4.1.143); MES, 2-(N-morpholino)ethane sulfonic acid monohydrate.     

Dose-dependent nonlinear response of the main phase-transition temperature of phospholipid membranes to alcohols

Summary The effect of 1-alkanols upon the main phase-transition temperature of phospholipid vesicle membranes between gel and liquid-crystalline phases was not a simple monotonic function of alkanol concentration. For instance, 1-decanol decreased the transition temperature at low concentrations, but increased it at high concentrations, displaying a minimal temperature. This concentration-induced biphasic effect cannot be explained by the van't Hoff model on the effect of impurities upon the freezing point. To explain this nonlinear response, a theory is presented which treats the effect of 1-alkanols (or any additives) on the transition temperature of phospholipid membranes in a three-component mixture. By fitting the experimental data to the theory, the enthalpy of the phase transition H ^* and the interaction energy, _AB ^* between the additive and phospholipid molecules may be estimated. The theory predicts that when _AB ^* >2 (where _AB ^* = _AB,/RT _o,T _o being the transition temperature of phospholipid), both maximum and maximum transition temperatures should exist. When _AB ^* = 2, only one inflection point exists. When _AB ^* < 2, neither maximum nor minimum exists. The alkanol concentration at which the transition temperature is minimum (X _min) depends on the _AB ^* value: the larger the _AB ^* values, the smaller theX _min. When _AB ^* is large enough,X _min values become so small that the plot T vs.X shows positive T in almost all alkanol concentrations. The interaction energy between 1-alkanols and phospholipid molecules increased with the increase in the carbon chain-length of 1-alkanols. In the case of the dipalmitcylphosphatidylcholine vesicle membrane, the carbon chain-length of 1-alkanols that caused predominantly positive T was about 12.     

Light-dependent modification of Photosystem II in spinach leaves

In dark-adapted spinach leaves approximately one third of the Photosystem II (PS II) reaction centers are impaired in their ability to transfer electrons to Photosystem I. Although these inactive PS II centers are capable of reducing the primary quinone acceptor, Q_A, oxidation of Q_A ^– occurs approximately 1000 times more slowly than at active centers. Previous studies based on dark-adapted leaves show that minimal energy transfer occurs from inactive centers to active centers, indicating that the quantum yield of photosynthesis could be significantly impaired by the presence of inactive centers. The objective of the work described here was to determine the performance of inactive PS II centers in light-adapted leaves. Measurements of PS II activity within leaves did not indicate any increase in the concentration of active PS II centers during light treatments between 10 s and 5 min, showing that inactive centers are not converted to active centers during light treatment. Light-induced modification of inactive PS II centers did occur, however, such that 75% of these centers were unable to sustain stable charge separation. In addition, the maximum yield of chlorophyll fluorescence associated with inactive PS II centers decreased substantially, despite the lack of any overall quenching of the maximum fluorescence yield. The effect of light treatment on inactive centers was reversed in the dark within 10–20 mins. These results indicate that illumination changes inactive PS II centers into a form that quenches fluorescence, but does not allow stable charge separation across the photosynthetic membrane. One possibility is that inactive centers are converted into centers that quench fluorescence by formation of a radical, such as reduced pheophytin or oxidized P680. Alternatively, it is possible that inactive PS II centers are modified such that absorbed excitation energy is dissipated thermally, through electron cycling at the reaction center.Abbreviations A518 absorbance change at 518 nm, reflecting the formation of an electric field across the thylakoid membrane - A_FL1 amplitude of the fast (<100 ms) phase of A518 induced by the first of two saturating, single-turnover flashes spaced 30 ms apart - A_FL2 amplitude of the fast (<100 ms) phase of A518 induced by the second of two saturating, single-turnover flashes spaced 50 ms apart - DCBQ 2,6-dichloro-p-benzoquinone - Fo yield of chlorophyll fluorescence when Q_A is fully oxidized - Fm yield of chlorophyll fluorescence when Q_A is fully reduced - Fx yield of chlorophyll fluorescence when Q_A is fully reduced at inactive PS II centers, but fully oxidized at active PS II centers - Pheo pheophytin - P680 the primary donor of Photosystem II - PPFD photosynthetic photon flux density - Q_A Primary quinone acceptor of PS II - Q_B secondary quinone acceptor of PS II     

AgNO3 increases type II callus production from immature embryos of maize inbred B73 and its derivatives

Incorporating 10 to 100 M AgNO₃ into Phytagel (0.2%) solidified N6 medium containing 1 mg/L 2,4-D, 100 mg/L casamino acids and 25 mM praline (N6 1-100-25) promoted type II callus production from cultured Zea mays L. immature embryos of FRB73, B73 X A188 and a proprietary B73 BC6 genotype. Under these conditions, approximately 15, 80 and 80% of the respective FRB73, B73 X A188 and B73 BC6 explants produced type II calli after 2 to 3 weeks incubation in the dark at 28 C. In the absence of AgNO₃, the type II culture response from B73BC6 immature embryos was 25% on N6 1 100-25 solidified with Phytagel (0.2%) as compared to 0% for that solidified with 0.8% agar. Duncan's medium was tested using 10 to 100 m AgNO₃ and generally promoted type I callus initiation, although up to 6% of the explants produced type II cultures in the presence of 0.2% Phytagel. Ethylene emanation rates of up to 370 and 115 nL g-1 h-1 were detected from B73 X A188 immature embryos and calli, respectively, cultured on N6 1-100-25.     

Fluorescence studies on interaction between phospho-LHC II and subchloroplast Photosystem 1 preparations

Chloroplast proteins were phosphorylated under two test conditions: white light irradiance alone and white light irradiance with the addition of glucose and glucose oxidase, used to produce an anaerobic medium. The interaction of phospho-LHC II with Photosystem 1 (PS 1) was studied for two types of PS I preparation. Changes in the chlorophyll a/b ratio and the ratio of 650 and 680 nm band intensities (E650/E680) in fluorescence excitation spectra were used in calculating the phospho-LHC II portion which became associated with PS 1. It is shown that the associated portion of phospho-LHC II varies for each of the PS 1 preparations and phosphorylation procedures. Possible conclusions as regards the transfer of various sets of LHC II subpopulations under different phosphorylation procedures and the differences of interaction with PS 1 are discussed.Abbreviations PS 1 Photosystem 1 - PS 2 Photosystem 2 - LHC II light-harvesting chlorophyll a/b protein complex II - Chl chlorophyll - fluorescence quantum yield - _f life time of fluorescence at =685 nm - F735 fluorescence band with a maximum at 735 nm - F685 fluorescence band with a maximum at 685 nm - E650/E680 ratio of amplitudes in excitation fluorescence spectrum at 650 and 680 nm     

Photosynthetic oxygen evolution: H/D isotope effects and the coupling between electron and proton transfer during the redox reactions at the oxidizing side of Photosystem II

The oxygen evolving complex (OEC) of Photosystem II (PS II) incorporates a Mn-cluster and probably a further redox cofactor, X. Four quanta of light drive the OEC through the increasingly oxidized states S0 S1 S2 S3 S4 to yield O2 during the transition S4 S0. It has been speculated that the oxidation of water might be kinetically facilitated by the abstraction of hydrogen. This implied that the respective electron acceptor is deprotonated upon oxidation. Whether YZ and X fulfill this expectation is under debate. We have previously inferred a 'chemical' deprotonation of X based on the kinetics of proton release (Haumann M, Drerenstedt W, Hundelt M and Junge W (1996) Biochim Biophys Acta 1273: 237–250. Here, we investigated the rates of electron transfer and proton release as function of the D2O/H2O ratio, the pH, and the temperature both in thylakoids and PS II core particles. The largest kinetic isotope effect on the rate of electron transfer (factor of 2.1–2.4) and the largest pH-dependence (factor of about 2 between pH 5 and 8) was found on S2 S3 where X is oxidized. During the other transitions both factors were much smaller ( 1.4). Electron transfer is probably kinetically steered by proton transfer only during S2 S3. These results corroborate the notion that X serves as a hydrogen acceptor for bound water during S4 S0. We propose a consistent scheme for the final reaction with water to yield dioxygen: two two-electron (hydrogen) transfers in series with a peroxide intermediate.