Field experiments were conducted to investigate the impact of simulated insect-caused defoliation on irrigated rice. Defoliation levels tested were 0% (control), 25% defoliation at 21 days after ...transplanting (dat), 25% defoliation at 41 dat, 25% defoliation at 21 and 42 dat, 50% defoliation at 21 dat, 50% defoliation at 42 dat, 75% defoliation at 21 dat, 75% defoliation at 42 dat, 75% defoliation at 21 and 42 dat, 100% defoliation at 21 dat, and 100% defoliation at 21 and 42 dat. Tiller height, total number of tillers, per cent panicle-bearing tillers, weight of 100 grains and grain yields were recorded. The rice plant when defoliated just before tillering or in the tillering stage has the ability to compensate for defoliation damage. No yield losses occurred at 25% defoliation. Defoliation of 100% had a significant effect on the total number of tillers and on grain yield. Yield losses at 100% defoliation over the 3 years of the study averaged 40% in the 21 dat treatment and 55% in the 21 and 42 dat treatment. The implications of the development of cultural practices to manage lowland rice defoliating insects are discussed.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Two methods for planting rice in irrigated lowland were evaluated during the wet seasons of 1994 and 1995 to determine their effect on rice arthropod numbers, insect-caused rice plant damage and rice ...grain yield. The six treatments tested were: hand transplanting of seedlings at spacings of 14 cm 2 14 cm, 20 cm 2 20 cm, and 30 cm 2 30 cm; and direct-seeding of rice at 60 kg seeds ha super(-1), 90 kg seeds ha super(-1) and 120 kg seeds ha super(-1). The most abundant arthropods in the study were the diopsid flies, Diopsis longicornis Maquart and D. apicalis Dalman; the green leafhoppers Nephotettix spp.; the white leafhoppers Cofana unimaculata (Signoret) and C. spectra (Distant); spiders; dragonflies and damselflies; and stem borers. There was no overall difference between transplanting and direct-seeding, or between plant densities, in regard to sweep net counts of Cofana spp. and spiders. Diopsis longicornis and D. apicalis adult numbers were highest in the 20 cm 2 20 cm transplanted plots in 1994, but no significant differences occurred in 1995. Nephotetttix spp. adult numbers were highest in the 120 kg seeds ha super(-1) direct-seeded plots in 1995 but no significant differences occurred in 1994. The percentage of tillers infested with stem borers was highest in the three transplanted and the 120 kg seed ha super(-1) direct-seeded treatments in 1994 and the three transplanted treatments in 1995. In 1995, the percentage of whiteheads (empty panicles) caused by stem borer feeding was highest in the directseeded treatments, increasing from the low rate of 60 kg seeds ha super(-1) to the highest rate of 120 kg seeds ha super(-1). Grain yields were generally similar in the transplanted and direct-seeded plots. Implications of planting methods and plant density as management practices in rice IPM and labour requirements for rice production are discussed.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Evidence favors a role for corticotropin-releasing factor (CRF) in learning and memory processes. A binding protein (CRF-BP) with the ability to inactivate CRF provides a novel target to modulate ...endogenous levels of CRF. The present studies employed three measures of information processing in rats in order to examine the impact of CRF system activation resulting from administration of CRF-BP ligand inhibitors, which increase levels of "free CRF." Acquisition of a visual discrimination paradigm and retention of a inhibitory avoidance task were dose dependently facilitated by central administration of a CRF-BP ligand inhibitor. CRF-BP ligand inhibitor treatment also improved performance in an active avoidance paradigm in aged animals. No nonspecific anorexic effects of the active dose of CRF-BP ligand inhibitor were detected in a food intake test. Moreover, the magnitude of in vivo efficacy of the CRF-BP ligand inhibitor peptide in producing a mild increase in motor activity was dissociated from that of a postsynaptic CRF receptor agonist that exerted robust and long-lasting activity increases. Thus, CRF-BP ligand inhibitors appear to elicit generalized learning enhancement effects without mimicking the robust nonspecific behavioral actions of a CRF receptor agonist.
Most free-living organisms require the synthesis and/or acquisition of purines and pyrimidines, which form the basis of nucleotides, to survive. In most bacteria, the nucleotides are synthesized de ...novo and the products are used in many cell functions, including DNA replication, energy storage, and as signaling molecules. Due to their central role in the metabolism of bacteria, both nucleotide biosynthesis pathways have strong links with the virulence of opportunistic and bona fide bacterial pathogens. Recent findings have established a new, shared link in the control of nucleotide biosynthesis and the production of virulence factors. Furthermore, targeting of these pathways forms the basis of interspecies competition and can provide an open source for new antimicrobial compounds. Here, we highlight the contribution of nucleotide biosynthesis to bacterial pathogenesis in a plethora of different diseases and speculate on how they can be targeted by intervention strategies.
De novo nucleotide biosynthesis is essential for the survival and virulence of pathogenic bacterial species in vitro and in vivo.Regulators of nucleotide biosynthesis are emerging as important for control of the expression of virulence factors.De novo nucleotide biosynthesis is targeted by purpose-specific molecules to facilitate bacterial survival during interspecies competition.Targeting of nucleotide biosynthesis can act as an antivirulence strategy, either on its own or in conjunction with existing antimicrobial therapies.
The branched-chain amino acids (BCAAs Ile, Leu, and Val) represent important nutrients in bacterial physiology, with roles that range from supporting protein synthesis to signaling and fine-tuning ...the adaptation to amino acid starvation. In some pathogenic bacteria, the adaptation to amino acid starvation includes induction of virulence gene expression: thus, BCAAs support not only proliferation during infection, but also the evasion of host defenses. A body of research has accumulated over the years to describe the multifaceted physiological roles of BCAAs and the mechanisms bacteria use to maintain their intracellular levels. More recent studies have focused on understanding how fluctuations in their intracellular levels impact global regulatory pathways that coordinate the adaptation to nutrient limitation, especially in pathogenic bacteria. In this minireview, we discuss how these studies have refined the individual roles of BCAAs, shed light on how BCAA auxotrophy might promote higher sensitivity to exogenous BCAA levels, and revealed pathogen-specific responses to BCAA deprivation. These advancements improve our understanding of how bacteria meet their nutritional requirements for growth while simultaneously remaining responsive to changes in environmental nutrient availability to promote their survival in a range of environments.
Iron is a versatile redox-active catalyst and a required cofactor within a diverse array of biological processes. To almost all organisms, iron is both essential and potentially toxic, where ...homeostatic concentrations must be stringently maintained. Within the iron-restricted host, the survival and proliferation of microbial invaders is contingent upon exploiting the host iron pool. Bacteria express a multitude of complex, and often redundant means of acquiring iron, including surface-associated heme-uptake pathways, high affinity iron-scavenging siderophores and transporters of free inorganic iron. Within the last decade, our understanding of iron acquisition by Gram-positive pathogens has expanded substantively, from the discovery of the iron-regulated surface-determinant pathway and numerous unique siderophores through to the detailed elucidation of heme–iron extraction, and heme and siderophore coordination and transfer. This review provides a comprehensive summary of the iron acquisition strategies of notorious Gram-positive pathogens and highlights how both conserved and distinct tactics for acquiring iron contribute to the pathophysiology of these bacteria. Further, a focus on recent structural and mechanistic studies details how these iron acquisition systems may be exploited in the development of novel therapeutics.
In this review, we discuss both the conserved and distinct strategies that Gram-positive pathogens use to acquire iron within the context of the iron-restricted host.
Summary
The success of Staphylococcus aureus as a pathogen is partly attributable to its ability to thwart host innate immune responses, which includes resisting the antimicrobial functions of ...phagocytes. Here, we have studied the interaction of methicillin‐resistant S. aureus (MRSA) strain USA300 with murine RAW 264.7 and primary human macrophages using molecular imaging and single cell analysis to obtain an unprecedented understanding of the interaction between the macrophage and MRSA. Herein we demonstrate that macrophages fail to control intracellular infection by MRSA USA300 despite trafficking the bacteria into mature phagolysosomes. Using fluorescence‐based proliferation assays we also show that intracellular staphylococci proliferate and that replication commences while the bacteria are residing in mature phagolysosomes hours after initial phagocytosis. Finally, live‐cell fluorescence video microscopy allowed for unprecedented visual insight into the escape of MRSA from macrophages, demonstrating that the macrophages die through a pathway characterized by membrane blebbing and activation of caspase‐3 followed by acquisition of the vital dye propidium iodide. Moreover, cell death precedes the emergence of MRSA from infected macrophages, and these events can be ablated by prolonged exposure of infected phagocytes to gentamicin.
Staphylococcus aureus requires branched-chain amino acids (BCAAs; isoleucine, leucine, valine) for protein synthesis, branched-chain fatty acid synthesis, and environmental adaptation by responding ...to their availability via the global transcriptional regulator CodY. The importance of BCAAs for S. aureus physiology necessitates that it either synthesize them or scavenge them from the environment. Indeed S. aureus uses specialized transporters to scavenge BCAAs, however, its ability to synthesize them has remained conflicted by reports that it is auxotrophic for leucine and valine despite carrying an intact BCAA biosynthetic operon. In revisiting these findings, we have observed that S. aureus can engage in leucine and valine synthesis, but the level of BCAA synthesis is dependent on the BCAA it is deprived of, leading us to hypothesize that each BCAA differentially regulates the biosynthetic operon. Here we show that two mechanisms of transcriptional repression regulate the level of endogenous BCAA biosynthesis in response to specific BCAA availability. We identify a trans-acting mechanism involving isoleucine-dependent repression by the global transcriptional regulator CodY and a cis-acting leucine-responsive attenuator, uncovering how S. aureus regulates endogenous biosynthesis in response to exogenous BCAA availability. Moreover, given that isoleucine can dominate CodY-dependent regulation of BCAA biosynthesis, and that CodY is a global regulator of metabolism and virulence in S. aureus, we extend the importance of isoleucine availability for CodY-dependent regulation of other metabolic and virulence genes. These data resolve the previous conflicting observations regarding BCAA biosynthesis, and reveal the environmental signals that not only induce BCAA biosynthesis, but that could also have broader consequences on S. aureus environmental adaptation and virulence via CodY.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this study we report, the synthesis of ZnO and its doping with Transition Metal Oxides -TMO-, such as Cr
O
, MnO
, FeO, CoO, NiO, Cu
O and CuO. Various characterization techniques were employed to ...investigate the structural properties. The X-ray diffraction (XRD) data and Rietveld refinement confirmed the presence of TMO phases and that the ZnO structure was not affected by the doping with TMO which was corroborated using transmission Electron microscopy (TEM). Surface areas were low due to blockage of adsorption sites by particle aggregation. TMO doping concentration in the range of 3.7-5.1% was important to calculate the catalytic activity. The UV-Visible spectra showed the variation in the band gap of TMO/ZnO ranging from 3.45 to 2.46 eV. The surface catalyzed decomposition of H
O
was used as the model reaction to examine the photocatalytic activity following the oxygen production and the systems were compared to bulk ZnO and commercial TiO
-degussa (Aeroxyde-P25). The results indicate that the introduction of TMO species increase significantly the photocatalytic activity. The sunlight photocatalytic performance in ZnO-doped was greater than bulk-ZnO and in the case of MnO
, CoO, Cu
O and CuO surpasses TiO
(P25-Degussa). This report opens up a new pathway to the design of high-performance materials used in photocatalytic degradation under visible light irradiation.
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