Comparative studies on glucose phosphorylating isoenzymes of vertebrates. Identification and characterization of amphibian liver hexokinases

Glucose phosphorylating activities were measured in liver extracts from two urodeles and twenty-six anurans. Fractionation on diethylaminoethyl-cellulose columns of liver extracts from these amphibians permitted the recognition of four hexokinases which are called A, B, C, and D. However, any given amphibian displays only three liver hexokinases and the profiles so far observed are either of the type A-B-D or C-B-D. The distribution of the amphibians in either type of pattern does not show any simple taxonomic relationship. A wide generic and specific, but not individual, variation of the relative proportion of each isoenzyme was observed. Hexokinases A and B were shown to be low K_{m glucose} isoenzymes (0.06 and 0.15 mm glucose, respectively) with normal hyperbolic kinetics. Hexokinase C, also a low K_m isoenzyme (0.05 mm) was found to be inhibited by excess substrate at physiological levels of glucose. Hexokinases A, B, and C were able to phosphorylate fructose, mannose, and 2-deoxyglucose at equal or higher rates than glucose when assayed at saturating sugar levels. Hexokinase D was found to be a high K_m isoenzyme ($\text{K}{}_{0.5}\text{? 2}\text{mM}$) with sigmoidal saturation curves for glucose (Hill coefficient ? 1.6). Fructose and mannose were also phosphorylated by this isoenzyme at about 70% of the glucose rate when studied at saturating sugar concentrations. The properties of the amphibian hexokinases are thus similar, although not identical, to those of mammalian hexokinases.     

Electrophysiological Responses to Alcohol Cues Are Not Associated with Pavlovian-to-Instrumental Transfer in Social Drinkers

Pavlovian to Instrumental Transfer (PIT) refers to the behavioral phenomenon of increased instrumental responding for a reinforcer when in the presence of Pavlovian conditioned stimuli that were separately paired with that reinforcer. PIT effects may play an important role in substance use disorders, but little is known about the brain mechanisms that underlie these effects in alcohol consumers. We report behavioral and electroencephalographic (EEG) data from a group of social drinkers (n = 31) who performed a PIT task in which they chose between two instrumental responses in pursuit of beer and chocolate reinforcers while their EEG reactivity to beer, chocolate and neutral pictorial cues was recorded. We examined two markers of the motivational salience of the pictures: the P300 and slow wave event-related potentials (ERPs). Results demonstrated a behavioral PIT effect: responding for beer was increased when a beer picture was presented. Analyses of ERP amplitudes demonstrated significantly larger slow potentials evoked by beer cues at various electrode clusters. Contrary to hypotheses, there were no significant correlations between behavioral PIT effects, electrophysiological reactivity to the cues, and individual differences in drinking behaviour. Our findings are the first to demonstrate a PIT effect for beer, accompanied by increased slow potentials in response to beer cues, in social drinkers. The lack of relationship between behavioral and EEG measures, and between these measures and individual differences in drinking behaviour may be attributed to methodological features of the PIT task and to characteristics of our sample.     

Adaptation of tobacco etch potyvirus to a susceptible ecotype of Arabidopsis thaliana capacitates it for systemic infection of resistant ecotypes

Viral pathogens continue to emerge among humans, domesticated animals and cultivated crops. The existence of genetic variance for resistance in the host population is crucial to the spread of an emerging virus. Models predict that rapid spread decreases with the frequency and diversity of resistance alleles in the host population. However, empirical tests of this hypothesis are scarce. Arabiodpsis thaliana—tobacco etch potyvirus (TEV) provides an experimentally suitable pathosystem to explore the interplay between genetic variation in host''s susceptibility and virus diversity. Systemic infection of A. thaliana with TEV is controlled by three dominant loci, with different ecotypes varying in susceptibility depending on the genetic constitution at these three loci. Here, we show that the TEV adaptation to a susceptible ecotype allowed the virus to successfully infect, replicate and induce symptoms in ecotypes that were fully resistant to the ancestral virus. The value of these results is twofold. First, we showed that the existence of partially susceptible individuals allows for the emerging virus to bypass resistance alleles that the virus has never encountered. Second, the concept of resistance genes may only be valid for a well-defined viral genotype but not for polymorphic viral populations.     

Root growth inhibition and ultrastructural changes in radish root tips after treatment with aqueous extracts of Fallopia japonica and F. ×bohemica rhizomes

Allelopathic compounds released by invasive alien plants can suppress the growth of plants in their vicinity. The aim of this study was to investigate changes in tissue and cell structure in roots of radish seedlings treated with 10% aqueous extracts of rhizomes from the invasive knotweeds Fallopia japonica and F. ×bohemica. After 7 days of growth without and with aqueous extracts from these rhizomes, the anatomical and ultrastructural changes in the radish seedling roots were analyzed with light and transmission electron microscopy, and hydrogen peroxide was localized with diaminobenzidine, to define oxidative stress. The roots of radish seedlings treated with the knotweed extracts were shorter and thicker, due to the shorter and wider shapes of their cortex cells, which were organized in more columns than the control roots. There were signs of cell damage and oxidative stress in the root cap cells, and to a lesser extent in the meristematic zone. As well as the irregularly shaped nuclei and plasma membrane detached from the cell wall, the most prominent ultrastructural effects in the root cap cells of these aqueous rhizome extracts were the ring-shaped form of the mitochondria and large endoplasmic reticulum bodies. Excessive vacuolization was seen for the cells of the root apical meristem.

     

Gobius xoriguer,a new offshore Mediterranean goby (Gobiidae), and phylogenetic relationships within the genus Gobius

Ichthyological Research - Gobius xoriguer sp. nov., a new ofshore species of goby (Teleostei: Gobiidae: Gobiinae) is described based on three specimens collected in 2010, 2012 and 2018 in the...     

Inter- and intra-molecular interactions of Arabidopsis thaliana DELLA protein RGL1

The phytohormone gibberellin and the DELLA proteins act together to control key aspects of plant development. Gibberellin induces degradation of DELLA proteins by recruitment of an F-box protein using a molecular switch: a gibberellin-bound nuclear receptor interacts with the N-terminal domain of DELLA proteins, and this event primes the DELLA C-terminal domain for interaction with the F-box protein. However, the mechanism of signalling between the N- and C-terminal domains of DELLA proteins is unresolved. In the present study, we used in vivo and in vitro approaches to characterize di- and tri-partite interactions of the DELLA protein RGL1 (REPRESSOR OF GA1-3-LIKE 1) of Arabidopsis thaliana with the gibberellin receptor GID1A (GIBBERELLIC ACID-INSENSITIVE DWARF-1A) and the F-box protein SLY1 (SLEEPY1). Deuterium-exchange MS unequivocally showed that the entire N-terminal domain of RGL1 is disordered prior to interaction with the GID1A; furthermore, association/dissociation kinetics, determined by surface plasmon resonance, predicts a two-state conformational change of the RGL1 N-terminal domain upon interaction with GID1A. Additionally, competition assays with monoclonal antibodies revealed that contacts mediated by the short helix Asp-Glu-Leu-Leu of the hallmark DELLA motif are not essential for the GID1A-RGL1 N-terminal domain interaction. Finally, yeast two- and three-hybrid experiments determined that unabated communication between N- and C-terminal domains of RGL1 is required for recruitment of the F-box protein SLY1.