Protein induced by bacteriophage T4 which is absent in Escherichia coli infected with nuclear disruption-deficient phage mutants.

A protein induced by wild-type T4 phage which is absent in Escherichia coli infected with nuclear disruption-deficient phage (with mutations in gene ndd) was identified by polacrylamide gel electrophoresis. This protein was synthesized at maximum rate at 3 to 6 min after infection. It had a molecular weight of 15,000 determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was associated with sedimentable fractions of the cell from which it can be dissociated with 1 M guanidine-hydrochloride. The dissociated protein can be partly recovered in a form soluble in dilute buffer after partial purification and dialysis. The occurrence of this protein in a particulate cell fraction is of interest because of the postulated role of the bacterial cell membrane in nuclear disruption.     

Augmented mitogenesis and impaired metabolic signaling mediated by a truncated insulin receptor

Recently, we have described a COOH-terminal deletion mutation of the human insulin receptor (HIR delta CT) that exhibits normal insulin-mediated kinase activity and endocytosis, but is inefficient in stimulating glucose transport and glycogen synthase (McClain, D. A., Maegawa, H., Levy, J., Huecksteadt, T., Dull, T. J., Lee, J., Ullrich, A., and Olefsky, J.M. (1988) J. Biol. Chem. 263, 8904-8911; Maegawa, H., McClain, D. A., Freidenberg, G., Olefsky, J. M., Napier, M., Lipari, T., Dull, T. J., Lee, J., and Ullrich, A. (1988) J. Biol. Chem. 263, 8912-8917). In this paper, we report that despite this defect in metabolic signaling, the truncated receptor exhibits augmented mitogenic activity compared to normal receptors. These results were verified in three independently isolated clones of Rat 1 fibroblasts transfected with the HIR delta CT cDNA. The increase in insulin sensitivity of mitogenic stimulation was proportional to the number of HIR delta CT receptors expressed on the cells. By contrast, only the cells with normal receptors and none of the HIR delta CT clones exhibit increased sensitivity for a metabolic action of insulin, the stimulation of glucose uptake. Stimulation of cells by other mitogens and autoradiographic analysis confirm that the enhanced mitogenic effects seen in HIR delta CT cells are attributable only to the presence of the truncated insulin receptors. These receptors mediate the tyrosine phosphorylation of a number of cellular proteins, and the pattern of these phosphorylations differs quantitatively from that seen in cells with normal receptors. We conclude: 1) The COOH terminus plays a role in signaling metabolic actions of insulin, perhaps through its recognition of substrates for the receptor kinase. 2) By contrast, the COOH terminus is an inhibitory regulator of mitogenesis, and removal of the terminal 43 amino acids converts the receptor from a moderately active growth signaler to a very active one. 3) The changes seen in biologic activities of the HIR delta CT receptor are associated with quantitative changes in substrate phosphorylation by the receptor kinase.     

Poly(ADP-Ribose) Polymerase Inhibition in Oxidant-Stressed Endothelial Cells Prevents Oncosis and Permits Caspase Activation and Apoptosis

Endothelial cells (EC) are subject to oxidative-induced cell death. Activation of poly(ADP-ribose) polymerase (PARP) occurs early in oxidant-induced EC injury and putatively mediates cell death by depleting its substrate, NAD⁺. In this study, the role of PARP in H₂O₂-induced EC death was investigated. EC were exposed to oxidant stress and viability continuously monitored using fluorescent dye exclusion. Inhibition of PARP with 1,5-dihydroxyisoquinoline (DIQ) delayed the time course of oxidant-induced EC death. Concurrent addition of the protein synthesis inhibitor, cycloheximide, or the endonuclease inhibitor, aurintricarboxylic acid, to PARP-inhibited cells further delayed the onset and attenuated the extent of H₂O₂-induced cell lysis, consistent with an active mode of cell death. Caspase-3-like activity, a hallmark of apoptosis, was negligible in oxidant-treated EC alone, however, inhibition of PARP by 3-aminobenzamide or DIQ dramatically increased caspase-3-like activity. Morphological assessment confirmed that the primary mode of death in oxidant-stressed EC was oncosis. However, following PARP inhibition, the cells switched to apoptosis. Since inflammation is associated with oncosis and not apoptosis, the results presented here could explain the beneficial effects seen with PARP inhibition in various in vivo models of oxidant injury and provide a mechanism to manipulate this injury into a state of cell death that could ultimately be controlled.     

Orchard floor management practices that maintain vegetative or biomass groundcover stimulate soil microbial activity and alter soil microbial community composition

Groundcover management systems (GMS) are important in managing fruit-tree orchards because of their effects on soil conditions, nutrient availability, tree growth and yields. We employed a polyphasic approach, incorporating measures of soil microbial abundance, activity and community composition, to study the long-term effects of different GMS on biotic and abiotic factors in an orchard soil. Four GMS treatments – Pre-emergence residual herbicides (Pre-H), post-emergence herbicide (Post-H), mowed-sod (Grass), and hardwood bark mulch (Mulch) – were established in 2-m-wide strips within tree rows in an apple orchard in 1992, and have been maintained and monitored annually until the present. We have measured soil water and nutrient availability, tree growth, and yields annually from 1993 to 2003. Soil nematode numbers and trophic groups were evaluated in July and Oct. 2001, and Sept. 2003. Numbers of culturable bacteria and fungi, soil respiratory activity, eubacterial and fungal community composition were determined in May and Sept. 2003. The Pre-H treatment soil had the fewest culturable bacteria, while the Grass treatment had the largest population of culturable fungi. Soil nematode population size and diversity were also affected by GMS treatments; the Pre-H treatment had the lowest ratio of (bacteriovores + fungivores) to plant parasitic nematodes. Soil respiration rates were higher in the Mulch than in other treatments during a 40-day incubation period. Hierarchical cluster dendrograms of denaturing gradient gel electrophoresis (DGGE) fingerprints for eubacterial community 16S rRNA genes indicated that Post-H and Grass treatments clustered together and separately from the Pre-H and Mulch treatments, which were also grouped together. The influence of GMSs on the fungal community, as assessed by PCR-DGGE of the internal transcribed spacer (ITS) region, was not as pronounced as that observed for bacteria. Soil fungal community composition under the Mulch differed from that under other treatments. The effects of GMS on soil microbial community abundance, activity, and composition were associated with observed differences in soil organic matter inputs and turnover, nutrient availability, and apple tree growth and yields under the different GMS treatments.     

Independent roles of Rho‐GTPases in growth cone and axonal behavior

Many external signals influence growth cone motility, pathfinding, and the formation of synapses that lead to the final map formation of the retinotectal system. Chick temporal retinal ganglion cell axons (RGCs) collapse and retract after encountering posterior tectal cells in vitro. During this process lateral extensions appear along the RGC axonal shaft. Lateral extensions appear as nascent interstitial axonal branches and also as defasciculating growth cones that are trailing along the pioneer axon. RGC branching controlled by repellent tectal cues has recently been shown to be the critical event in retinotectal map development. The intracellular mechanism underlying this phenomenon, however, is not understood. Inhibiting RhoA with either C3 toxin or inhibiting p160Rock kinase, an effector of RhoA, with Y27632 inhibited collapse, retraction, and the number of axons that showed lateral extensions. Lateral extension length increased significantly. Inhibiting Rac1A and cdc42 with cell permeable peptide inhibitors did not inhibit collapse of growth cones, but did inhibit axon retraction. In addition, the number of axons that showed lateral extensions and lateral extension length were significantly reduced. A dynamic cytoskeleton is necessary to react to incoming guidance information. This study addresses the problems of how growth cone motility and branching or defasciculation are affected by Rho‐GTPases as extracellular signals are transmitted to the cytoskeleton. © 2002 Wiley Periodicals, Inc. J Neurobiol 54: 358–369, 2003     

Spatial aggregation facilitates coexistence and diversity of wild plant species in field margins

European agri-environment schemes encourage farmers to establish sown field margin strips to protect and enhance wild plant diversity. However, plant diversity in such wild plant sowings based on seed mixtures is often low due to the high competitiveness of few, common species. Here we analysed whether intraspecific aggregation could enhance the performance of less competitive species, and how plant performance is influenced by the number of species in a mixture. We focused on inter- and intraspecific competition between six agricultural wild plant species (Centaurea cyanus, Calendula arvensis, Melilotus officinalis, Poa annua, Bromus mollis, Medicago lupulina), and tested (i) two different seeding patterns (intraspecifically aggregated vs. randomly dispersed) and (ii) three different species mixtures (monocultures, three-species, and six-species mixtures). Plant performance was measured in terms of number of individuals, biomass per individual, and biomass per m². Intraspecific aggregation resulted in higher numbers of individuals of all species, while mixtures generated lower numbers of individuals. The performance of plant species differed depending on their position in the competitive hierarchy. Competitively weak species suffered much less from intraspecific than interspecific competition in terms of biomass, and the competitively weakest species became even excluded in the most species rich and randomly dispersed sowings with high interspecific competition. In conclusion, the performance of wild plant species was influenced by both seeding pattern and number of species in a mixture. Intraspecific aggregation enabled the coexistence of competitively weak species by reducing interspecific competitive exclusion processes. Consequently, agri-environmental schemes designed to preserve and enhance biodiversity should consider small-scale processes influencing the distribution and abundance of plants, and develop new agricultural sowing technologies to cultivate competitively weak and endangered wild plant species.     

Seed dormancy release and germination characteristics of <i>Corispermum lehmannianum</i> Bunge,an endemic species in the Gurbantunggut desert of China

Seed dormancy release and germination of Corispermum lehmannianum Bunge were tested using various treatments: temperature, cold stratification, gibberelins (GA3), dry storage and sand burial. Results showed that temperature and light did not affect the germination of fresh seeds, cold stratification and GA3 could improve seed germination, whereas dry storage and sand burial did not. The germination percentage was highest at 35/20 °C after the cold stratification and GA3 treatments. Corispermum lehmannianum seeds were classified as non-deep, Type-2, physiological dormancy (PD), whose seed dormancy could be released by cold stratification and GA3.