Anaerobic metabolism of Nitrosomonas europaea

Nitrosomonas europaea is capable of maintaining an anaerobic metabolism, using pyruvate as an electron donor and nitrite as an electron acceptor; utilization of nitrite depends upon supply of both pyruvate and ammonia. The role of ammonia in this reaction was not determined. N europaea also assimilates CO₂ anaerobically into cell material in the presence of nitrite (0.5–1.0 mM), pyruvate and ammonia. This reaction was partially inhibited by nitrite which apparently competed with CO₂ for reducing power. Anaerobic nitrite respiration is sensitive to ionophores, FCCP being the most effective.Non-standard-abbreviations TCA trichloroacetic acid - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazon     

Mineralization budgets in sediment microcosms: Effect of the infauna and anoxic conditions

Abstract A number of sediment incubations were set up to reproduce some of the conditions used by Kristensen and Blackburn [1] and to make a comparison with their results. There were three types of microcosm: aerobic (OX), anaerobic (AN) and aerobic with Nephtys (NOX). In addition to other measurements, dissolved organic nitrogen (DON) pools and fluxes, were measured. The sediment in this experiment contained more particulate organic matter (POM). Nephtys (NOX) had the same effect as Nereis in increasing the rate of mineralization of POC and PON, compared with the OX-cores (2.1 and 2.6 times, respectively). Again, the AN-cores had a higher mineralization rate (loss of POM) than that of the OX-cores, but in addition, mineralization in NOX-cores was not significantly different from AN-cores. It was thus confirmed that anoxic mineralization could be as high, or higher, than the oxic process. Both the temporal patterns of O₂-and and CO₂-fluxes and their magnitudes were very similar to those reported earlier. This contrasts with the higher loss of POM in the present experiment. However, the loss of C in DOC (associated with the measured DON) can account for the extra POM loss. The pore-water profiles of σCO₂ and NH₄⁺ were similar to those in the earlier report, and the fluxes of σCO₂, O₂, NH₄⁺ and NO₃⁻ followed the same temporal pattern.     

Effects of rapid changes in oxygen concentration on the respiration of carrot roots

Rates of CO₂ production and O₂ consumption from aged disks of carrot ( Daucus carota L.) root tissues were measured for 4 h after they were transferred from 21% to 0, 1, 2, 4 or 8% O₂ in gas mixtures. A transient peak in the rate of CO₂ production started 5 to 7 min after transfer to 2% or lower O₂ mixtures and peaked at 50 min. After the peaks in CO₂ production from the 0, 1 and 2% O₂ treatments and after the stable production from the 4 and 8% O₂ treatments, the rate of CO₂ production from all low O₂ treatments started to decline at 50 min, reaching stable rates by 160 to 240 min. Concentrations of lactate and ethanol that were significantly higher than the 21% O₂ controls had started to accumulate in disks between 10 and 50 min after exposure to atmospheres containing 2% or less O₂. Production of CO₂ started to increase 5 to 7 min after transfer to 0, 1 and 2% O₂, while the initial decline and then rise in pH and the accumulation of ethanol did not occur until 30 min after the change in atmosphere. Ethanol accumulation paralleled the increase in pH; first at 0.4 μmol g⁻¹ h⁻¹ from 30 to 60 min as the pH shifted from 5.97 to 6.11, and then at 0.08 μmol g⁻¹ h⁻¹ from 60 to 100 min as the pH stablized around 6.12. The peak at 50 min in CO₂ production roughly coincided with the shift from the rapid to the slow change in pH and ethanol accumulation.     

Surface heterogeneity of bovine sperm revealed by aqueous two-phase partition

Ejaculated, bovine sperm have been subjected to multiple partition in aqueous two-phase systems. This partition, carried out in a countercurrent fashion, reveals heterogeneity of the sperm population with respect to surface properties. The sperm, when partitioned in phase systems that detect non-change associated surface properties (change-insensitive) are largely distributed as two distinct populations. In charge-sensitive phase systems (which principally detect cell surface molecules carrying charge) the sperm do not show any obvious surface heterogeneity. Considerable heterogeneity is revealed in affinity-ligand phase systems containing palmitic acid coupled to one of the phase components-poly(ethylene glycol). There is a difference in surface heterogeneity between sperm which have been washed in buffer or left unwashed, direct from the ejaculate. This is indicative of weak adsorption of proteins to the sperm surface in seminal fluid. These results show that bovine ejaculated sperm is a heterogeneous cell population having unequal distributions of a number of different surface molecules.     

Adherence of Agrobacterium tumefaciens to the cells of immature wheat embryos

Agrobacterium attached to wheat embryos in vitro. This attachment was plasmid independent, and occurred on both wounded and unwounded cell surfaces. The pattern of attachment clearly demonstrated that bacterial attachment to cereal cells follows the same trends observed for dicotyledonous plants. During the inoculation period the bacterial cells attach to the plant cell walls either with lateral or polar orientation. Wounding (mechanical or enzymatic) preferentially promoted adherence of the bacteria at the wound site, however, attachment was not wound dependent.     

Restriction enzyme digestion of heterochromatin inDrosophila nasuta

In situ digestion of metaphase and polytene chromosomes and of interphase nuclei in different cell types ofDrosophila nasuta with restriction enzymes revealed that enzymes like AluI, EcoRI, HaeIII, Sau3a and SinI did not affect Giemsa-stainability of heterochromatin while that of euchromatin was significantly reduced; TaqI and SalI digested both heterochromatin and euchromatin in mitotic chromosomes. Digestion of genomic DNA with AluI, EcoRI, HaeIII, Sau3a and KpnI left a 23 kb DNA band undigested in agarose gels while withTaqI, no such undigested band was seen. TheAluI resistant 23 kb DNA hybridized insitu specifically with the heterochromatic chromocentre. It appears that the digestibility of heterochromatin region in genome ofDrosophila nasuta with the tested restriction enzymes is dependent on the availability of their recognition sites.     

Dietary modulation of α-amylase activity in eight geographical strains of Sitophilus oryzae and Sitophilus zeamais

Rank transformation of specific activity values of -amylase across four strains of Sitophilus oryzae (L.) and four strains of S. zeamais Motschulsky indicates that levels of these predominant enzymes are highest in adults feeding on hulled barley or long-grain brown rice. Intermediate activity levels are found in weevils feeding on yellow corn (maize) and lowest levels are found in wheat-fed weevils. Although extracts prepared from barley contain inhibitory activity against two purified isoamylases from S. oryzae, levels of the naturally-occurring -amylase inhibitors against these two enzymes are about 2.2-fold and 6.1-fold, respectively, more concentrated in wheat. Ingestion of these amylase inhibitors and formation of an inactive enzyme:inhibitor complex with previously secreted amylase may account for the lower activity of amylase in weevils of both species feeding on wheat. Amylase levels across all strains feeding on a given diet are about 2-fold higher in S. oryzae than in S. zeamais. Significant differences in activity levels were also found between strains in both species. Since -amylase is a predominant digestive hydrolase in these species, the degree to which cereal diets affect amylase levels may indicate their suitability as potential hosts.

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Résumé La transformation de rang des valeur d'activité spécifique de l'-amylase de 4 souches de S. oryzae et de 4 souches de S. zeamais montre que les niveaux les plus élevés de ces enzymes prédominantes s'observent chez les adultes nourris d'orge mondé ou de riz brun á grains longs. Des niveaux intermédiaires d'activité ont été obtenus chez les insectes élevés sur maïs jaune, et les niveaux les plus faibles chez ceux élevés sur blé. Bien que les extraits préparés à partir d'orge présentent une activité inhibitrice de deux isoamylases purifiées de S. oryzae, les niveaux des inhibiteurs naturels -amylase de ces deux enzymes sont environ respectivement 2,2 et 6,1 fois plus concentrés dans le blé. L'ingestion de ces inhibiteurs d'amylase et la formation d'un complexe enzyme inactive/inhibiteur avec l'amylase secrétée antérieurement, peut rendre compte de la plus faible activité de l'amylase chez les charançons consommant du blé. Le niveau d'amylase de S. oryzae est 2 fois plus élevé que celui de S. zeamais pour toutes les souches élevées sur un régime donné. Des niveaux d'activité significativement différents ont été trouvés suivant les souches pour chacune des deux espèces. Puisque l'amylase est la principale hydrolase digestive de ces espèces, l'intensité de la modification des teneurs en amylase par la consommation de céréales peut indiquer leur adéquation comme hôtes potentiels.

     

狗的无氧阈与骨骼肌某些特征在锻炼、脱锻炼动态变化中的关系

本实验在体力锻炼与脱锻炼过程中观察了五条成年雄性杂种狗的无氧阈(AT)、骨骼肌毛细血管密度(cap/mm~2)、毛细血管数与肌纤维数之比(C:F)、肌纤维组成——慢肌纤维百分比(％ST)以及毛细血管弥散距离(弥散距离)的变化。结果表明:锻炼前AT与cap/mm~2、C:F,％ST及弥散距离均分别有显著相关。锻炼后第五周,AT、cap/mm~2、C:F和％ST分别增加了40.9％、12.2％、22.9％和2.4％,弥散距离降低6.3％,其中只有AT的增加有显著意义,锻炼十周后,AT增加68.2％(P<0.001)、cap/mm~2增加37.8％(P<0.05)、C:F增加78.1％(P<0.001),弥散距离降低17.0％(P<0.01)而％ST无显著变化。停止锻炼后第五周,AT等各指标都有降低的趋势,但无显著意义,停止锻炼后第12周,AT、cap/mm~2,C:F,％ST分别降低了18.9％、10.9％、10.5％、2.9％,弥散距离增加5.1％,其中除AT的降低有显著意义外,其余指标的变化均无显著意义。与锻炼前相比,这些指标的变化。除％ST外,仍有显著变化。在锻炼与脱锻炼的过程中,AT与cap/mm~2、C:F、弥散距离在各期或整个过程中均呈显著相关,但与％ST相关不显著。实验结果提示,骨骼肌的毛细血管供应状况是决定无氧阈的重要因素之一。     

Mechanism for Cd2+ inhibition of (K++ Mg2+)ATPase activity and K+ (86Rb+) uptake join roots of sugar beet (Beta vulgaris)

Steady state kinetics were used to examine the influence of Cd²⁺ both on K⁺ stimulation of a membrane-bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K⁺(⁸⁶Rb⁺) uptake in intact or excised beet roots. The in vitro effect of Cd²⁺ was studied both on a 12000–25000 g root fraction of the (Na⁺+K⁺+Mg²⁺)ATPase and on the ATPase when further purified by an aqueous polymer two-phase system. The observed data can be summarized as follows: 1) Cd²⁺ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd²⁺ at concentrations <100 μM inhibits the specific K⁺ activation at both high and low affinity sites for K⁺. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K⁺ <5 mM, the inhibition by Cd²⁺ with respect to K⁺ is uncompetitive. In the presence of MgATP and K⁺ >10 μM, the inhibition by Cd²⁺ is competitive. 3) At the low concentrations of K⁺, Cd²⁺ also inhibits the 2,4-dinitrophenol(DNP)-sensitive (metabolic) K⁺(⁸⁶Rb⁺) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP-insensitive (non metabolic) K⁺(⁸⁶Rb⁺) uptake is little influenced by Cd²⁺. As Cd²⁺ inhibits the metabolic uptake of K⁺(⁸⁶Rb⁺) and the K⁺ activation of the ATPase in the same way at low concentrations of K⁺, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K⁺ is low, the presence of Cd²⁺ could be disadvantageous.     

Molecular analysis of the inheritance and stability of the mitochondrial genome of an inbred line of maize

Summary We have investigated the inheritance of the mitochondrial DNA (mtDNA) restriction endonuclease digestion patterns of maize inbred line B37N in individual plants and pooled siblings in lineages derived from five separate plants in the third generation following successive self-pollinations. The restriction fragment patterns of the different mtDNA samples were compared after digestion with five endonucleases. No differences were visible in the mobilities of the 199 fragments scored per sample. Hybridization analysis with two different cloned mtDNA probes, one of which contains homologies to a portion of the S2 plasmid characteristic of cms-S maize, failed to reveal cryptic variation. The apparent rate of genomic change in maize mtDNA from inbred plants appears to be very slow, compared with the faster rates of change seen in maize tissue cultures and with the documented rapid rate of inter- and intraspecific variation for mammalian mtDNA.