Identification of Photosynthetic Mutants of Arabidopsis by Automatic Screening for Altered Effective Quantum Yield of Photosystem 2

Quantification of chlorophyll (Chl) fluorescence is a versatile tool for analysing the photosynthetic performance of plants in a non-intrusive manner. A pulse-amplitude modulated fluorometer was combined with a CNC router for the automated measurement of the effective quantum yield of photosystem 2 (₂) of Arabidopsis thaliana plants. About 90 000 individual plants representing 7 500 lines derived from En-transposon and T-DNA mutagenised Arabidopsis populations were screened for mutants with altered ₂. Forty-eight recessive ₂ mutations were identified of which most exhibit also altered pigmentation and increased photosensitivity. For three ₂ mutants the corresponding mutated genes were identified that code all for chloroplast-located proteins. Comparison of the ₂ mutant screen with other screening methods based on the measurement of Chl fluorescence shows that the ₂ mutants identified are different to mutants identified by high Chl fluorescence. Some ₂ mutants, on the contrary, are common to mutants identified by screens based on non-photochemical quenching.     

Physiological relationship between the temperate phages lambda and phi80

Summary This work deals with the ability of phage 80 to provide defective mutants of with their missing functions. Functions Involved in Recombination. As shown by others, the Int mechanism of 80 cannot excise prophage . However, 80 efficiently excises recombinants from tandem dilysogens, using its Ter mechanism. Likewise, the nonspecific mechanism Red is interchangeable between 80 and . Maturation of DNA by 80. The Ter recombinants excised by 80 from tandem dilysogens are packaged into a 80 protein coat. This contrasts with the fact, already mentionned by Dove, that 80 is extremely inefficient for packaging phage superinfecting a -lysogen. The latter result is also found when the helper phage is a hybrid with the left arm of (80hy4 or 80hy41 — see Fig. 1). However, the maturation of the superinfecting is much more efficient if the 80hy used as a helper has the att-N region of (like 80hy1). Conversely a with the att-N region of 80 (hy6 — see Fig. 1) is packaged more efficiently by 80 or 80hy4 than by 80hy1. It is suggested that the maturation of chromosome superinfecting an immune cell requires a recombination with the helper phage. Vegetative Functions. Among the replicative functoons O and P, the latter only can be supplied by 80. That N mutants are efficiently helped by 80 does not tell that 80 provides the defective with an active N product; the chromosomes are simply packaged into a 80 coat. This shows that 80 is unable to switch on the late genes of . That neither 80 nor any of the 80hy tested can provide an active N product is shown in a more direct way by their complete failure to help N ^-r₁₄; this phage carries a polar mutation which makes the expression of genes O and P entirely N-dependant. The maturation of a N ^- by 80 contrasts with the fact that mutants affected in late genes (A, F or H) are not efficiently helped by 80. This suggests that the products coded by these genes are not interchangeable between 80 and , and that packaging of DNA into 80 coats is possible but inhibited when late proteins are present in the cell. Activation of the Late Genes. Among the im ₈₀ h ⁺ hybrids tested, only 80hy41 is able to switch on the late genes of a N defective mutant. This hybrid differs from the other hybrids studied here, by the fact that it has the Q-S-R region of (see Fig. 1). The results are consistant with the view that the product of Q gene is sufficient for activating the late genes of a DNA. N would thus control the expression of late genes only indirectly by controlling the expression of gene Q (Couturier & Dambly have independantly reached the same conclusion, 1970). Furthermore the failure of 80 and of the 80hy1 and 80hy4 to activate the late genes of would imply that these phages are unable to provide an Q product active on the chromosome Reciprocally, switches on the late genes of prophage 80hy41, but not of prophages 80hy1 and 80hy4. This suggests that the initiation of late genes expression takes place at a main specific site located in the Q-S-R region of the chromosome. The expression of the late genes would thus be sequential, and proceed through the left arm only when steaky ends cohere. Similar conclusions were reached independantly by Toussaint (1969) and by Herskowitz and Signer (1970).

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Ce travail a été réalisé dans le cadre du contrat d'association Euratom-U. L. B. 007-61-10 ABIB et avec l'aide du Fonds de la Recherche Fondamentale Collective.     

Host factor requirements and some properties of ΦXtB

Summary Replication of XtB, a capsid mutant of bacteriophage X174, depends on the host functions directed by the E. coli genes dnaE, dnaF, dnaG, dnaZ, lig and rep. The cellular products of dnaA, dnaB, dnaC(D), dnaI, dnaP, polA, polB and xth genes are, however, dispensable for the viral growth. In these host factor requirements, XtB resembles phages K and St-1, rather than X174. Host ranges of XtB, St-1 and K overlap considerably, and growth temperature of the three phages is somewhat higher than that of X174. Furthermore, XtB is, like K, inactivated by antiserum against St-1. XtB may thus fill an evolutionary gap between the X174 group and the St-1 group.     

Ecology of Proteus flagellar phages

Summary Phages identical to X ₇ in host range and serological properties are liberated by several Proteus strains. Another Proteus flagellar phage, X ₈, differs from X ₇ antigenically and in host range.     

Sinking properties of some phytoplankton shapes and the relation of form resistance to morphological diversity of plankton – an experimental study

Form resistance () is a dimensionless number expressing how much slower or faster a particle of any form sinks in a fluid medium than the sphere of equivalent volume. Form resistance factors of PVC models of phytoplankton sinking in glycerin were measured in a large aquarium (0.6 × 0.6 × 0.95 m). For cylindrical forms, a positive relationship was found between and length/width ratio. Coiling decreased in filamentous forms. Form resistance of Asterionella colonies increased from single cells up to 6-celled colonies than remained nearly constant. For Fragilaria crotonensis chains, no such upper limit to was observed in chains of up to 20 cells (longer ones were not measured). The effect of symmetry on was tested in 1–6-celled Asterionella colonies, having variable angles between the cells, and in Tetrastrum staurogeniaeforme coenobia, having different spine arrangements. In all cases, symmetric forms had considerably higher form resistance than asymmetric ones. However, for Pediastrum coenobia with symmetric/asymmetric fenestration, no difference was observed with respect to symmetry. Increasing number and length of spines on Tetrastrum coenobia substantially increased . For a series of Staurastrum forms, a significant positive correlation was found between arm-length/cell-width ratio and : protuberances increased form resistance. Flagellates (Rhodomonas, Gymnodinium) had a < 1: they sank faster than the spheres of equivalent volume. Ceratium ( = 1.61) proved an exception among flagellates: in most forms tested in this study (ellipsoid flagellates, Staurastrum forms with no or very short protuberances, and Cosmarium forms), > 1. The highest value ( = 8.1) was established for a 20-celled Fragilaria crotonensis chain. Possible origin of the so-called `vital component' (a factor that shows how much slower viable populations sink than morphologically similar senescent or dead ones) is discussed, as is the role of form resistance in evolution of high diversity of plankton morphologies.An erratum to this article can be found at     

Mapping of temperature sensitive mutants of bacteriophage phi 29

Summary Temperature-sensitive mutants of eleven complementation groups of phage 29 have been mapped by means of two-factor crosses. The results show the existence of a single non-circular linkage map. Cistrons expressed early after infection are clustered at the left end of the map.     

Noradrenaline induced secretion of nonelectrolytes through frog skin

Summary Addition of noradrenaline (4×10^–5 m) to the inner bathing fluid in the skin of the frogRana esculenta results in increased unidirectional fluxes of urea, thiourea, N-methyl-thiourea, N-N-dimethylthiourea and mannitol. Fluxes towards the external medium ( ₀) undergo a much greater increase than those moving in the opposite direction ( _i ). The effect of noradrenaline on ( ₀) is higher for urea and thiourea than mannitol, while its effect on ( ₀) thiourea derivatives is related to lipid solubility. This phenomenon does not occur for ( _i ) of the same molecules.FCCP (10^–6 m) pretreatment strongly inhibits the noradrenaline effect on ( ₀). In skin pretreated whith colchicine (2×10^–5 m) both urea fluxes are increased to the same extent by noradrenaline. Noradrenaline is concluded to exert two separate effects: (1) a change in permeability in both directions; (2) a secretion of nonelectrolytes towards the external fluid. Such secretion is most probably associated with the hormone-induced secretion of fluid and electrolytes, perhaps mediated by an exocytotic mechanism.     

Isolation of a halobacterial phage with a fully cytosine-methylated genome

Summary A new bacteriophage from Halobacterium halobium has been isolated and partially characterized. It is not homologous to the phage H (Schnabel, et al. 1982) which infects the same bacterium, though it appeared spontaneously in a culture of H adapted to H. halobium NRL/JW. The size and morphology of N are comparable to that of other known halophages. The genome of N consists of linear double-stranded DNA, 56 kb in size, whose dCMP is totally replaced by 5-methyl-dCMP. This is the second case of a fully cytosine-methylated genome, the bacteriophage XP12 from Xanthomonas oryzae, being so far the only one reported. Like H, the N, genome seems to have terminal redundancy and circular permutation. N is the first halobacterial phage which survives prolonged exposure to low ionic strength environments. After 48 h incubation in distilled water a loss in infectivity of less than 50% is observed.     

Different Relationship Between Electron Transport and CO2 Assimilation in two Zea mays Cultivars as Influenced by Increasing Irradiance

Gas exchange and fluorescence parameters were measured simultaneously in two Zea mays L. cultivars (Liri and 121C D8) to assess the relationship between the quantum yield of electron transport (_PS2) and the quantum yield of CO₂ assimilation (_CO2) in response to photosynthetic photon flux density (PPFD). The cv. Liri was grown under controlled environmental conditions in a climate chamber (CC) while cv. 121C D8 was grown in CC as well as outdoors (OT). By exposing the two maize cultivars grown in CC to an increasing PPFD, higher photosynthetic and photochemical rates were evidenced in cv. Liri than in cv. 121C D8. In Liri plants the _PS2/_CO2 ratio increased progressively up to 27 with increasing PPFD. This suggests that the reductive power was more utilised in non-assimilatory processes than in CO₂ assimilation at high PPFD. On the contrary, by exposing 121C D8 plants to increasing PPFD, _PS2/_CO2 was fairly constant (around 11–13), indicating that the electron transport rate was tightly down regulated by CO₂ assimilation. Although no significant differences were found between _PS2/_CO2 of the 121C D8 maize grown under CC and OT by exposing them to high PPFD, the photosynthetic rate and photochemical rates were higher in OT maize plants.     

Leaf anthocyanin content changes in Zea mays L. grown at low temperature: Significance for the relationship between the quantum yield of PS II and the apparent quantum yield of CO2 assimilation

The quantum yield of non-cyclic electron transport from PS II (PS II) and the apparent quantum yield of CO2 fixation (CO2) were measured in the maize genotype, R-CH HOPI, which shows a high leaf anthocyanin content when grown at a temperature slightly below 20 °C. Thus, the leaf anthocyanin content was thirty-five times higher in plants grown at 18 °C when compared to plants grown at 23 °C. The relationship between PS II and CO2 obtained at different CO2 partial pressure was linear for plants with both high and low leaf anthocyanin content. The PS II/CO2 ratio was about 16 in plants with high leaf anthocyanin content and about 10 in plants with low leaf anthocyanin content. The leaf light absorptance in the 400–700 nm region was higher in plants with higher leaf anthocyanin content. Since leaf absorptance between 400 and 600 nm and leaf anthocyanin content also resulted in a strict linear relationship, an indirect estimation of the absorbed light by leaf anthocyanins and thus at chloroplasts was derived. Using the correct estimation of the absorbed light at chloroplasts, to obtain CO2, differences in PS II/CO2 ratios between plants with different leaf anthocyanin content were eliminated. The modulation of leaf anthocyanin content by growth temperature is regarded as an effective strategy to modulate the light available at the chloroplasts.     

Virulence as a consequence of genome instability of a novel temperate bacteriophage, ΦRsG1, of Rhodobacter sphaeroides Y

A novel temperate bacteriophage, designated RsG1, was isolated from Rhodobacter sphaeroides Y (previously designated Rhodopseudomonas sphaeroides) following exposure to mitomycin C. The phage morphology, as revealed from electron microscopy, showed a hexagonal head (90 by 46.5 nm) connected with a tail (116 by 9.4 nm), to which a collar was proximally attached. A morphologically similar phage was also produced by spontaneous lysis of the cells. While RsG1 did not grow on any other bacterial strain tested, spontaneously produced phage particles propagated (and formed plaques) on R. sphaeroides Y still carrying RsG1 in the prophage state. The genome of RsG1 consisted of double stranded linear DNA with cohesive ends and a GC-content of 71.8 mol%. The DNA molecules formed circles in vitro with a mean contour length of 17.18±0.4 m, which corresponds to a size of 49 kbase pairs (kb). On the other hand, DNA extracted from the virulent phage particles was heterogeneous and consisted of two DNA species of different size, occurring in a ratio of about 1:1. These molecules also circularized having contour lengths of 17.18±0.4 m and 14.02±0.41 m corresponding to 49 and 40 kb, respectively. Restriction digest analysis of the two DNA species and DNA from RsG1 indicated that they are similar, and allowed the indentification of an 11.5 kb EcoRI fragment that carries the cohesive ends. Because DNA from RsG1 and the 49 kb DNA of the virulent phage particles were indistinguishable with the criteria applied, it is suggested that phage particles containing the 40 kb DNA represent the virulent type of phage, termed RsG1.1.     

Photosynthetic capacity and nitrogen partitioning among species in the canopy of a herbaceous plant community

Partitioning of nitrogen among species was determined in a stand of a tall herbaceous community. Total amount of nitrogen in the aboveground biomass was 261 mmol N m^–2, of which 92% was in three dominant species (Phragmites, Calamagrostis and Carex) and the rest was in the other eight subordinate species. Higher nitrogen concentrations per unit leaf area (n _L) with increasing photosynthetically active photon flux density (PPFD) were observed in all species except for three short species. The changes in n _L within species were mainly explained by the different nitrogen concentrations per unit leaf mass, while the differences in n _L between species were explained by the different SLM (leaf mass per unit leaf area). Photon absorption per unit leaf nitrogen ( _N ) was determined for each species. If photosynthetic activity was proportional to photon absorption, _N should indicate in situ PNUE (photosynthetic nitrogen use efficiency). High _N of Calamagrostis (dominant) resulted from high photon absorption per unit leaf area ( _area ), whereas high _N of Scutellaria (subordinate) resulted from low n _L although its _area was low. Species with cylinder-like leaves (Juncus and Equisetum) had low _N , which resulted from their high n _L. Light-saturated CO₂ exchange rates per unit leaf area (CER) and per unit leaf nitrogen (potential PNUE) were determined in seven species. Species with high CER and high n _L (Phragmites, Carex and Juncus) had low potential PNUE, while species with low CER and low n _L showed high potential PNUE. NUE (ratio of dry mass production to nitrogen uptake) was approximated as a reciprocal of plant nitrogen concentration. In most species, three measures of nitrogen use efficiency (NUE, _N and potential PNUE) showed strong conformity. Nitrogen use efficiency was high in Calamagrostis and Scutellaria, intermediate in Phragmites and relatively low in Carex. Nitrogen use efficiency of subordinate species was as high as or even higher than that of dominant species, which suggests that growth is co-limited by light and nitrogen in the subordinate species.     

Unigenic and multigenicI region control of the immune responses of mice to the GAT10 and GLΦ-GLT terpolymers

Recombinant strains of mice with known alleles in theI region of theH-2 complex were used to map theH-2 linked immune response genes controlling responsiveness to random terpolymers GAT¹⁰ and GL. TheIr-GAT gene was mapped to either theIA orIB subregions. In contrast, data obtained in the GL-GLT system indicated multigenic control. The responsiveness of the B10.A(3R), B10.A(5R), and B10.S(9R) recombinants indicated that one immune response gene,IrGL-GLT _A, mapped to the right ofIB, i.e., in theIC subregion. The nonresponsiveness of the B10.A(1R), B10.A(2R), B10.M(17R), and AQR mice having responderIC ^d alleles butIA ^k-IB ^k nonresponder alleles and the positive response of a (C57BL/6 × A/J)F₁ hybrid derived from two nonresponder parental strains indicated the presence of a second gene inIA-IB subregions,Ir-GL-GLT _B. The interaction between these two genes, each present in a differentI subregion, controls the immune response.     

The isolation and characterization of TabR bacteria: Hosts that restrict bacteriophage T4 rII mutants

Summary We have isolated mutants of Escherichia coli B (called TabR) that restrict the growth of bacteriophage T4 rII mutants at high temperature. TabR strains lysed very rapidly after infection with rII mutants, and no progeny phage were produced. T4⁺-infected TabR cells also lysed quickly, but the cells remained intact long enough to give a small burst. We have selected pseudorevertants of rII deletion mutants that grow on TabR at high temperature; tk (thymidine kinase) is a component of one class of these pseudorevertants.T4 strains harboring mutations in genes 12, 16, 25, 34, 36, 45 and 63 were also specifically restricted on TabR strains at high temperature. Bacteriophages T2, T4, T5, T6, and T7 grew normally on TabR, while , 80, and P1 failed to grow at any temperature. The most restrictive TabR strains were auxotrophic for methionine at high temperature, and most spontaneous Met⁺ revertants had also lost the ability to restrict rII mutants, suggesting that the TabR phenotype and methionine auxotrophy result from the same mutation.Although the mechanism by which TabR strains exert their restriction has not been determined, one model is described. The potential uses of these and similar strains is discussed.     

Quantifying Protein Folding Transition States with ΦT

A number of reaction coordinates have been proposed for reduced-dimensionalityrepresentations of a protein's folding free energy surface. We discuss in detail the entropic reaction coordinate _T = SS, recently introduced to quantify the conservation of mutations and the location of the folding transition state based on experimental temperature-tuning data. Numerical simulations illustrate the advantages as well as the limitations of _T. _T can be determined from experiment,computation, and analytical theory; _T can also be used to investigate structurally localized perturbations of the free energy surface. However, _T is only a relative reaction cordinate; furthermore, proteins undergo cold denaturation at sufficiently low temperatures, and care must be taken ininterpreting _T near the region where G/T = 0, particularly if the heat capacity change upon folding is small.     

The Instron technique as a measure of immediate-past wall extensibility

The relationship between the plastic-extensibility values (PEx) obtained in the Instron technique and the growth parameter, wall extensibility () has been evaluated for Avena sativa L. coleoptile cell walls. The possibility that PEx is proportional to the growth rate rather than to has been eliminated by showing that turgor-driven changes in the growth rate do not cause comparable changes in PEx. For Avena coleoptiles, PEx appears to be a measure of the average over the previous 60–90 min rather than a measure of the instantaneous of the growth equation. This is indicated by the fact that while PEx and the growth rate start to change simultaneously after addition of indole-3-acetic acid or KCN, the growth rate reaches a new, constant value 60–90 min before a new plateau value of PEx is obtained. Similar results are obrained with soybean (Glycine max L.) hypocotyl walls, indicating that the relationship between PEx and the parameter is a general one, although the period over which is averaged differs from tissue to tissue. In addition, it is shown that PEx can be measured more than once on the same section; a new potential for plastic extension is regenerated whenever the force vectors are changed even slightly. It is concluded that PEx is a measure of those domains in the wall where a wall-loosening event has occurred which has not been eliminated by further wall synthesis or other biochemical events.Abbreviations and symbols DP Instron plastic compliance - IAA indole-3-acetic acid - PEx Instron plastic extensibility - instantaneous wall extensibility     

Molecular Dynamics Simulations on the Coenzyme Thiamin Diphosphate in Apoenzyme Environment

Thiamin diphosphate (ThDP) is an essential cofactor for a number of enzymes, and especially involved in the nonoxidative decarboxylation of -keto acids by pyruvate decarboxylase (PDC). Recently the crystal structure of PDC bound ThDP has been determined. Based on these X-ray data MD simulations of the isolated coenzyme as well as of ThDP in its enzymatic environment were performed, using the GROMOS87 software package. For the ThDP-apoenzyme modelling all significant amino acid residues with a cut-off radius less than 8.5 Å from the cofactor were taken into account.Because the activity of the coenzyme mainly depends on the formation of a specific structure, the conformational behavior of ThDP and enzyme bound ThDP were investigated within the MD simulations in more detail. Therefore, trajectories of significant structural parameters such as the ring torsion angles _T and _P as well as essential hydrogen bonds were analyzed by our graphics tool. Moreover, Ramachandran-like plots with respect to the torsion angles _T and _P were used for the illustration of preferred orientations of the two aromatic rings in ThDP.Finally, MD simulations on ThDP analogs with less or none catalytic activity and apoenzyme mutants were included, in order to get hints of conformational effects and significant interactions in relation to cofactor-apoenzyme binding and the catalytic mechanism.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s0089460020312     

Two useful dimensionless parameters that combine physiological, operational and bioreactor design parameters for improved control of dissolved oxygen

Two new dimensionless parameters ( and ) are proposed for calculating the proportional, integral, and derivative constants of a dissolved oxygen proportional integral-derivative (PID) feed-back control algorithm from knowledge of the growth rate, bioreactor design and operation variables. The values of and were determined for a broad range of Reynolds numbers (between 1000 to 40 000) during the exponential growth phase of two highly different processes: fermentations of recombinant Escherichia coli and cultures of human hematopoietic cells. The utility of and for use in dissolved oxygen self-tunning adaptive control algorithms is discussed.