Synergistic effects of ethanol and temperature on yeast mitochondria

At temperatures lower than 37°C, the ethanol inhibition constant (Ki) for growth or fermentation inrho ⁺ cells of theSaccharomyces cerevisiae strain S288C was always higher (1.1M) than inrho ^– mutants (0.7M). At 37°C these differences disappeared, and both strains were equally inhibited by ethanol (Ki=0.7m). Mitochondrial activity can be inhibited by high ethanol concentration and temperature. In fact, the stronger inhibition by ethanol of therho ⁺ strain at 37°C was due to the fact that, under these conditions, this strain loses the advantage conferred by mitochondrial activity since the induction ofrho ^– cells in the population is very high. This does not result in an increase in the frequency ofrho ^– mutants because of the poor viability of these mutants in conditions of high temperature and ethanol. In consequence, S288C strain becomes as strongly inhibited by ethanol as therho ^– mutant strains. Differences in viability were not related to the fatty acids and ergosterol composition of the strain. In the presence of ethanol, bothrho ⁺ andrho ^– strains modified their lipids in the same way, but these changes did not improve their ethanol tolerance. They were not due to differences in adaptation to ethanol either, since after successive transfers in ethanol, growth () and fermentation () rates in therho ^– mutants were increasingly inhibited with time, whereas in the S288C strain inhibition of and by ethanol remained unaltered. Rather,rho ^– mutants are less viable thanrho ⁺ cells because of the inability of the former to respire. At 37°C the Ki increased to 0.9M ethanol either when mitochondrial from highly ethanol-tolerant wine yeasts were transferred torho ^– mutants of the strain S288C or when the mitochondria of strain S288C were preadapted by growing the strain in glycerol instead of glucose before it was cultivated in ethanol.     

Nucleotide sequences of the tolA and tolB genes and localization of their products, components of a multistep translocation system in Escherichia coli.

Various mutations in the tolQRAB gene cluster of Escherichia coli render the bacteria tolerant to high concentrations of the E, A, or K colicins as well as tolerant to infection by the single-stranded filamentous bacteriophage. The nucleotide sequence of a 2.8-kilobase fragment containing the tolA and tolB genes was determined. This sequence predicts TolA to be a 421-amino-acid protein of molecular mass 44,190 daltons. Studies using minicells show it to be associated with the inner membrane, presumably via a 21-amino-acid hydrophobic sequence between residues 13 and 35. The remaining 387 residues on the carboxyl side of this region are located in the periplasm. Within this region of TolA is a 230-residue portion that is predicted to form a very long helical segment. This region is rich in alanine, lysine, and glutamic and aspartic acids. The TolB protein is predicted to contain 431 amino acids. Localization studies using minicells show two proteins encoded by this open reading frame. The larger protein of 47.5 kilodaltons appears to be associated with the membrane fractions. The smaller protein is 43 kilodaltons in size and is found with the periplasmic components of the cell.     

Short-term influence of nitrate on acetylene reduction, net photosynthesis and nodule respiration in black alder (alnus glutinosa L. gaertn.) seedlings

The use of nitrogen-fixing trees such as black alder (Alnus glutinosa L. Gaertn.) as forest silvicultural tools has recently been recognized. The potential benefit of black alder in silvicultural practices may be reduced by nitrate fertilization. Fifteen-month-old, nodulated, black alder rooted cuttings were fertilized for 6 days with 0, 7.5 or 15 mM NO₃ to determine the influence of nitrate on acetylene reduction, nodule respiration and net photosynthesis. Acetylene reduction, net photosynthesis and nodule respiration were measured on the second, fourth and sixth days of nitrate application. Nitrate treatment significantly reduced acetylene reduction and nodule respiration by day 4. Acetylene reduction was 75% lower and nodule respiration 36% lower for the 15 mM NO₃ treatment when compared to that of the control treatment. By day 6, net photosynthesis and nodule respiration were significantly reduced by 29 and 59%, respectively, for seedlings treated with 15 mM NO₃. This study suggests that nitrate fertilization has a profound influence on nitrogenase activity and that nitrogen-fixing tree species may respond to nitrate fertilization by shifting photosynthetic rates.     

Interplay between carbohydrate in the stalk and the length of the connecting peptide determines the cleavability of influenza virus hemagglutinin.

The ability of many viruses to replicate in host cells depends on cleavage of certain viral glycoproteins, including hemagglutinin (HA). By generating site-specific mutant HAs of two highly virulent influenza viruses, we established that the relationship between carbohydrate in the stalk and the length of the connecting peptide is a critical determinant of cleavability. HAs that lacked an oligosaccharide side chain in the stalk were cleaved regardless of the number of basic amino acids at the cleavage site, whereas those with the oligosaccharide side chain resisted cleavage unless additional basic amino acids were inserted. This finding suggests that the oligosaccharide side chain interferes with HA cleavage if the number of basic amino acids at the cleavage site is not adequate to nullify this effect. Similar interplay could influence cleavage of other viral glycoproteins, such as those of human and simian immunodeficiency viruses and paramyxoviruses.     

Presence of the bacterial hemoglobin gene improves α-amylase production of a recombinantEscherichia coli strain

A recombinant plasmid (pMK57) was constructed by cloning theBacillus stearothermophilus α-amylase gene into pUC8; plasmid pMK79 was then derived from pMK57 by inserting the bacterial (Vitreoscilla) hemoglobin gene into the latter plasmid. Both pMK57 and pMK79 were transformed intoEscherichia coli strain JM103 to make strains MK57 and MK79, respectively. Both MK57 and MK79 produced α-amylase and MK79 produced hemoglobin. MK79 outgrew MK57 in shake flasks in LB medium, the advantage of the former appearing in late log phase. MK79 produced more α-amylase than MK57, on both per cell and per volume bases, in both mid and late log phases; the maximum advantage of MK79 (on a per volume basis) occurred in late log phase, at which time it produced 3.3 times as much α-amylase as MK57. The numbers of copies per cell of both pMK57 and pMK79 were significantly lower than that of pUC8.     

Quantitative analysis of the combined effects of temperature, evaporative demand and light on leaf elongation rate in well-watered field and laboratory-grown maize plants

The respective effects of meristem temperature, vapour pressuredeficit (VPD) and photosynthetic photon flux density (PPFD)on leaf elongation rate (LER) of maize, in the absence of waterdeficit in the soil have been quantified. This analysis wascarried out in a series of field experiments in northern andsouthern France over several seasons and years, and in growthchamber experiments. LER was measured with 10 min steps, togetherwith meristem temperature, VPD and PPFD at leaf level in threetypes of experiments: in growth chamber experiments with stepsin PPFD or VPD at constant meristem temperature, in growth chamberexperiments with several combinations of constant, but contrasting,PPFDs, VPDs and meristem temperatures, and in the field withfluctuating conditions, (i) When evaporative demand was low(night or day with low air VPD), LER was only linked to meristemtemperature, regardless of other climatic conditions, (ii) Lighthad no effect per se on LER in the range from 0 to 1500 molm^–2 s^–1 for time-scales longer than 2 h, providedthat its indirect effects on meristem temperature and on evaporativedemand were corrected (in the growth chamber) or taken intoaccount (in the field), and provided that cumulated PPFD overa weekly time-scale was compatible with field conditions, (iii)Evaporative demand sensed by growing leaves, as estimated bymeristem-to-air vapour pressure difference, markedly affectedLER in the range from 1–4 kPa, at all time-scales understudy, with a unique relationship in the growth chamber (constantconditions) and in the field (fluctuating conditions). Thiseffect was only observed when PPFD was high enough for stomatato open. The negative effect of evaporative demand on LER wasprobably not due to long distance root-to-shoot signalling,since soil was wet, calculated root water potential remainedclose to 0 MPa and concentration of ABA in the xylem sap wasvery low. Therefore, it is proposed to model maize LER witha two-step process, involving the calculation of the maximumLER at a given meristem temperature and then the calculationof the reduction in LER due to evaporative demand. Joint analysisof the whole set of data by using the two equations yieldeda r² of 0.75. This two-step process would be more accurate thanthe provision of LER from temperature only in cases where airVPD frequently exceeds 2 kPa. Key words: Leaf growth, light, evaporative demand, temperature, thermal time, water deficit, ABA, Zea mays L.     

Distribution and breeding biology of offshore cichlids in Lake Malawi/ Niassa

Synopsis Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km², and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. bigeye, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the large Rhamphochromis group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices.