Zymomonas mobilis mutants blocked in fructose utilization

Summary A mutant ofZymomonas mobilis deficient in the utilization of fructose for growth and ethanol formation was shown to lack fructokinase activity. When grown in media which contained glucose+fructose or sucrose, both the mutant and wild type produced sorbitol in amounts up to 60 g·l^-1, depending on the initial concentrations of sugars. Sorbitol formation was accompanied by an accumulation of acetaldehyde, gluconate, and acetoin. A ferricyanide-dependent sorbitol dehydrogenase could be localized in the cell membrane; it thus resembles the sorbitol dehydrogenase ofGluconobacter suboxydans. Neither a NAD(P)H dependent reduction of fructose nor a NAD(P) dependent dehydrogenation of sorbitol could be detected in cell-free extracts. The use of fructose-negative mutants ofZ. mobilis for the enrichment of fructose in glucose+fructose mixtures is discussed.     

Use of calcium to optimize long-term proliferation of friable embryogenic calluses and plant regeneration in Hevea brasiliensis (Mll. Arg.)

In Hevea brasiliensis (Mll. Arg.), increasing the calcium contentof the friable callus maintenance medium from 3 to 9 mM stimulatedregeneration potential through somatic embryogenesis. This stimulationcould be attributed to the homogeneous cytological structureof calluses, which were formed of undifferentiated cells capableof somatic embryogenesis in optimal culture conditions. Thevery marked increase in the active cell population was sufficientto cause a decrease and a stabilization of water and osmoticpotentials of the calluses, whereas their water content increased.The regeneration capacity of calluses cultured on a medium withadditional CaCl₂ was greater in terms of both quantity (numberof somatic embryos produced was increased 2-fold) and quality(germination efficiency trebled). High CaCl₂ concentrations (9 mM CaCl₂) in the embryogenesisinduction medium favoured somatic embryo development when calluseswere maintained 2 months on the same medium. In this case, additionof benzylaminopurine (BAP) and 3,4-dichlorophenoxy- acetic acid(3,4-D) increased the number of embryos produced (243 embryosg^–1 FW callus) and their germination capacity (27%). These culture conditions were used to determine the optimumembryogenesis induction period. The length of the period affectedboth the intensity of embryogenesis (maximum 56–77 d)and somatic embryo quality (maximum 49–70 d). The bestresults were obtained with a 70 d embryogenesis induction period,within which 355 embryos g^–1 FW callus were obtained,with 35% germination. Key words: Calcium, somatic embryogenesis, long-term culture, water status, histology     

Ionophore-mediated Ca2+ countertransport: role of Na+, Li+ or H+ gradient

Summary In an artificial system, the ionophore A23187, which transports Ca²⁺ but not Na⁺, is able to mediate the uphill translocation of Ca²⁺ from one aqueous medium to another across an organic immiscible phase, provided that a Na⁺, Li⁺ or H⁺ gradient is imposed on the system. Therefore, in the process known as Na-Ca countertransport, the downhill influx of Na⁺ may not be necessary for causing Ca²⁺ extrusion against its electrochemical gradient.     

The genetics of phenotypic plasticity. IV. Chromosomal localization

The contributions of each chromosome to the traits thorax size and plasticity of thorax size as affected by temperature in Drosophila melanogaster were measured. A composite stock was created from lines previously subjected to selection on thorax size or plasticity of thorax size. A chromosome extraction was performed against a uniform background lacking genetic variation, provided by a stock of marked balancer flies. With regard to amount of plasticity, chromosome I and the balancer stock showed no plasticity, the composite stock showed the greatest plasticity, and chromosomes II and III were intermediate. Chromosome I showed significant genetic variation for thorax size at both 19° C and 25° C, but not for plasticity, while chromosome II showed significant genetic variation for plasticity, but not for thorax size. Chromosome III showed significant genetic variation for both thorax size and plasticity. We tested the predictions of three models of the genetic basis of phenotypic plasticity: overdominance, pleiotropy, and epistasis. The results support the epistasis model, in agreement with earlier work. The amount of developmental noise was correlated with phenotypic plasticity at 25° C, in agreement with earlier work. A negative correlation was found at 19° C for chromosome II, contrary to earlier work.     

Binding of epithelial cells to lectin-coated surfaces

Summary Epithelial cells may relate to their basement membrane substrates via lectin-like interactions. In a model system for study of this type of interaction, lectin-coated bacteriological plastic petri dishes were presented as substrates for epithelial cell adhesion. Of 21 lectins tested by mixed agglutination against two epithelial cell types, Madin-Darby canine kidney (MDCK), and human embryonic kidney cells (HEK), nine gave less than 5% rosettes and 12 gave 5 to 50% rosettes. Wheat germ agglutinin (WGA) andGeodia cydonium lectin gave the highest percentage of rosettes. Wheat germ agglutinin was readily adsorbed to plastic surfaces and maintained specificity in binding interactions. Both MDCK and HEK cells attached as well to WGA coated petri dishes as to conventional tissue culture dishes. Furthermore, both spread over the lectin-coated surfaces. The MDCK cells grew to confluence and could be subcultured and maintained indefinitely on such surfaces, although WGA in solution was toxic to the cells in concentrations as low as 0.1 to 1.0 μg/ml. Cell attachment to WGA coated dishes was blocked by cycloheximide only if the cells had been preincubated with the inhibitor for several hours. Cell attachment was not inhibited by pretreatment of cells with neuraminidase. Precoating cells with WGA blocked binding to both WGA-coated surfaces and untreated tissue culture dishes. Cells attached to WGA-coated dishes could not be readily dislodged by trypsin-EDTA for the first 2 h after subculture. By 4 h, attachment was again trypsin sensitive, suggesting that the cells synthesized a trypsin-sensitive material that was laid down between the cell surface and the WGA-coated dish. Regeneration of trypsin sensitivity was not blocked by cycloheximide. This work was supported by Research Grant AG01986 from the National Institutes of Health, Bethesda, Maryland.     

In vivo activation of blood and arterial prophospholipase by an activator of blood platelet origin]

When partially purified platelet-rat lysate is injected in the rat aorta, transformation of prophospholipase into phospholipase is observed. Blood prophospholipases are activated almost entirely during about 15 minutes; aortic phospholipase are entirely activated for a longer time.     

The breakthrough paradox: How focusing on one form of innovation jeopardizes the advancement of science

Research needs a balance of risk‐taking in “breakthrough projects” and gradual progress. For building a sustainable knowledge base, it is indispensable to provide support for both. Subject Categories: Careers, Economics, Law & Politics, Science Policy & Publishing

Science is about venturing into the unknown to find unexpected insights and establish new knowledge. Increasingly, academic institutions and funding agencies such as the European Research Council (ERC) explicitly encourage and support scientists to foster risky and hopefully ground‐breaking research. Such incentives are important and have been greatly appreciated by the scientific community. However, the success of the ERC has had its downsides, as other actors in the funding ecosystem have adopted the ERC’s focus on “breakthrough science” and respective notions of scientific excellence. We argue that these tendencies are concerning since disruptive breakthrough innovation is not the only form of innovation in research. While continuous, gradual innovation is often taken for granted, it could become endangered in a research and funding ecosystem that places ever higher value on breakthrough science. This is problematic since, paradoxically, breakthrough potential in science builds on gradual innovation. If the value of gradual innovation is not better recognized, the potential for breakthrough innovation may well be stifled.

While continuous, gradual innovation is often taken for granted, it could become endangered in a research and funding ecosystem that places ever higher value on breakthrough science.

Concerns that the hypercompetitive dynamics of the current scientific system may impede rather than spur innovative research have been voiced for many years (Alberts et al, 2014). As performance indicators continue to play a central role for promotions and grants, researchers are under pressure to publish extensively, quickly, and preferably in high‐ranking journals (Burrows, 2012). These dynamics increase the risk of mental health issues among scientists (Jaremka et al, 2020), dis‐incentivise relevant and important work (Benedictus et al, 2016), decrease the quality of scientific papers (Sarewitz, 2016) and induce conservative and short‐term thinking rather than risk‐taking and original thinking required for scientific innovation (Alberts et al, 2014; Fochler et al, 2016). Against this background, strong incentives for fostering innovative and daring research are indispensable.     

A physiological and molecular study of the effects of nickel deficiency and phenylphosphorodiamidate (PPD) application on urea metabolism in oilseed rape (Brassica napus L.)

Background and aims

Urea is the major nitrogen (N) form supplied as fertilizer in agriculture. However, urease, a nickel-dependent enzyme, allows plants to use external or internally generated urea as a nitrogen source. Since a urease inhibitor is frequently applied in conjunction with urea fertilizer, the N-metabolism of plants may be affected. The aim of this study was to determine physiological and molecular effects of nickel deficiency and a urease inhibitor on urea uptake and assimilation in oilseed rape.

Methods

Plants were grown on hydroponic solution with urea as the sole N source under three treatments: plants treated with nickel (+Ni) as a control, without nickel (?Ni) and with nickel and phenylphosphorodiamidate (+Ni+PPD). Urea transport and assimilation were investigated.

Results

The results show that Ni-deficiency or PPD supply led to reduced growth and reduced ¹⁵N-uptake from urea. This effect was more pronounced in PPD-treated plants, which accumulated high amounts of urea and ammonium. Thus, Ni-deficiency or addition of PPD, limit the availability of N and decreased shoot and root amino acid content. The up-regulation of BnDUR3 in roots indicated that this gene is a component of the stress response to nitrogen-deficiency. A general decline of glutamine synthetase (GS) activity and activation of glutamate dehydrogenase (GDH) and increases in its expression level were observed in control plants. At the same time, in (?N) or (+Ni+PPD) treated plants, no increases in GS or GDH activities and expression level were found.

Conclusions

Overall results showed that plants require Ni as a nutrient (while most widely used nutrient solutions are devoid of Ni), whether they are grown with or without a urea supply, and that urease inhibitors may have deleterious effects at least in hydroponic grown oilseed rape.