NUTRIENT TRANSFER IN VESICULAR-ARBUSCULAR MYCORRHIZAS: A NEW MODEL BASED ON THE DISTRIBUTION OF ATPases ON FUNGAL AND PLANT MEMBRANES

In this paper we review the membrane transport processes that are involved in the transfer of mineral nutrients and organic  carbon between  the  symbiotic partners  in mycorrhizas.  In particular, we  reassess  the prevailing hypothesis that transfer in vesicular-arbuscular (VA) mycorrhizas occurs  simultaneously and bidirectionally across the same interface and that arbuscules are the main sites of transfer. Using cytochemical techniques, we and our collaborators have reexamined the distribution of ATPases in the arbuscular and intercellular hyphal interfaces in VA mycorrhizas formed between roots of Allium cepa (onion) and the fungus Glomus intraradices. The results showed that H+-ATPases have different localisation on plant and fungal membranes in arbuscular and hyphal interfaces (Gianinazzi-Pearson et al. 1991). While some arbuscular interfaces had H+-ATPase activity on both fungal and plant membranes, in most cases the fungal membrane lacked this activity.  In contrast, the plasma membranes of intercellular hyphae always had H+-ATPase and the adjacent root cells did not. This suggests that the different interfaces in a VA mycorrhiza may have different functions. We propose that passive loss of P from the arbuscules is associated with active uptake by the energised (ATPase-bearing) plant membrane and that passive loss of carbohydrate from the root cells is followed by active uptake by the intercellular hyphae. If this model is correct, then variations in "mycorrhizal efficiency" (i.e. the extent to which mycorrhizal plants grow better than non-mycorrhizal controls) might be determined by differences in the numbers of active arbuscules as a proportion of the total fungal biomass within the root. As  a  first  step  towards  investigating  this  possibility, we  have  developed methods  for measuring  the surface areas of arbuscular and hyphal interfaces in different fungus-host combinations, Glomus spp./ Allium porrum (leek). We have also measured fluxes of P from fungus to plant and have been able to partition these between the arbuscular and total (arbuscular plus hyphal) interfaces.  The implications of this work, and suggestions for future investigations of the molecular mechanisms involved in nutrient transfer in mycorrhizas, are discussed.Key words: Mycorrhizas/Glomus intraradices/ATPases/Allium cepa

Suppression of monocyte and neutrophil function by recombinant IL-2

Little IS known about the influence of IL-2 on phagocytes. We now describe the effects of human recombinant IL-2 on human neutrophil and monocyte functions related to mobility, phagocytosis, glucose uptake, respiration and degranulation. Neutrophil adherence and hexose monophosphate shunt activities were both suppressed after incubation with IL-2. IL-2 had no effect on neutrophil migration, phagocytosis, deoxyglucose uptake or degranulation, ionocytes demonstrated a greater sensitivity to IL-2 with suppression of monocyte adherence, random and stimulated migration, glucose uptake and hexose monophosphate shunt activity, even after addition of phorbol myristate acetate. Monocyte phagocytosis and degranulation were not affected. All of the effects observed were dose-dependent within a biologically active range for IL-2. These studies suggest that IL-2 may have an important down-regulatory role across a broad range of monocyte functions including movement, deoxyglucose uptake and respiration. However, its role in regulation of neutrophil function is limited to adherence and respiration. IL-2 may be a more versatile cytokine than has previously been appreciated

Are silica defences in grasses driving vole population cycles?

Understanding the factors that drive species population dynamics is fundamental to biology. Cyclic populations of microtine rodents have been the most intensively studied to date, yet there remains great uncertainty over the mechanisms determining the dynamics of most of these populations. For one such population, we present preliminary evidence for a novel mechanism by which herbivore-induced reductions in plant quality alter herbivore life-history parameters and subsequent population growth. We tested the effect of high silica levels on the population growth and individual performance of voles (Microtus agrestis) reared on their winter food plant (Deschampsia caespitosa). In sites where the vole population density was high, silica levels in D. caespitosa leaves collected several months later were also high and vole populations subsequently declined; in sites where the vole densities were low, levels of silica were low and population density increased. High silica levels in their food reduced vole body mass by 0.5% a day. We argue that silica-based defences in grasses may play a key role in driving vole population cycles

Bat and pig IFN-induced transmembrane protein 3 restrict cell entry by influenza virus and lyssaviruses

IFN-induced transmembrane protein 3 (IFITM3) is a restriction factor that blocks cytosolic entry of numerous viruses that utilize acidic endosomal entry pathways. In humans and mice, IFITM3 limits influenza-induced morbidity and mortality. Although many IFITM3-sensitive viruses are zoonotic, whether IFITMs function as antiviral restriction factors in mammalian species other than humans and mice is unknown. Here, IFITM3 orthologues in the microbat (Myotis myotis) and pig (Sus scrofa domesticus) were identified using rapid amplification of cDNA ends. Amino acid residues known to be important for IFITM3 function were conserved in the pig and microbat orthologues. Ectopically expressed pig and microbat IFITM3 co-localized with transferrin (early endosomes) and CD63 (late endosomes/multivesicular bodies). Pig and microbat IFITM3 restricted cell entry mediated by multiple influenza haemagglutinin subtypes and lyssavirus glycoproteins. Expression of pig or microbat IFITM3 in A549 cells reduced influenza virus yields and nucleoprotein expression. Conversely, small interfering RNA knockdown of IFITM3 in pig NPTr cells and primary microbat cells enhanced virus replication, demonstrating that these genes are functional in their species of origin at endogenous levels. In summary, we showed that IFITMs function as potent broad-spectrum antiviral effectors in two mammals – pigs and bats – identified as major reservoirs for emerging viruses

Excited-State Dynamics of a Two-Photon-Activatable Ruthenium Prodrug

We present a new approach to investigate how the photodynamics of an octahedral ruthenium(II) complex activated through two-photon absorption (TPA) differ from the equivalent complex activated through one-photon absorption (OPA). We photoactivated a RuII polypyridyl complex containing bioactive monodentate ligands in the photodynamic therapy window (620–1000 nm) by using TPA and used transient UV/Vis absorption spectroscopy to elucidate its reaction pathways. Density functional calculations allowed us to identify the nature of the initially populated states and kinetic analysis recovers a photoactivation lifetime of approximately 100 ps. The dynamics displayed following TPA or OPA are identical, showing that TPA prodrug design may use knowledge gathered from the more numerous and easily conducted OPA studies

Double marking revisited

In 2002, the Qualifications and Curriculum Authority (QCA) published the report of an independent panel of experts into maintaining standards at Advanced Level (A-Level). One of its recommendations was for: ‘limited experimental double marking of scripts in subjects such as English to determine whether the strategy would signi-ficantly reduce errors of measurement’ (p. 24). This recommendation provided the impetus for this paper which reviews the all but forgotten literature on double marking and considers its relevance now

Effect of headlocks on milk production and feed intake of dairy cattle

Cows previously trained with headlocks did not increase milk production or feed intake when headlocks were removed. Twoyear- old and older cows did not differ in response to headlocks and neckrails. Prudent use of headlocks increases labor efficiency of a commercial dairy. Managing a dairy without headlocks is a challenge because cows must be sorted and worked off the milking parlor flow. In the case of large milking parlors, it may be necessary to process 50-200 cows per hour. Depending upon the treatment facilities, this number of cows may create a bottleneck in the dairy. For many routine procedures, headlocks offer the simplest and most cost-effective alternative. It is important to note that headlocks can be mismanaged. This is especially true during summer months. Locking up cows for extended periods without access to water or shade may have adverse effects during summer heat stress. It is important to minimize lock-up time. Consideration should also be given to training heifers to headlocks prior to calving. It is very likely that untrained heifers may be reluctant to be placed in headlocks. If this occurs, intake could be limited during their first exposure to headlocks. If heifers are not trained to headlocks prior to calving, one should determine if they should be locked-up each day during the first week of lactation. Headlocks can be successfully used on a dairy. The critical question is how will they be managed. Successful managers of headlocks minimize restraint time, push-up or feed pens often (6- 8 times per day), and avoid use of headlocks during late morning and afternoon hours during the summer months

Systematics of Charged-Particle Products from Reactions Induced by 95-MeV 6-Li

This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit

Hosts of Type II Quasars: an HST Study

Type II quasars are luminous Active Galactic Nuclei whose centers are obscured by large amounts of gas and dust. In this contribution we present 3-band HST images of nine type II quasars with redshifts 0.25<z<0.4 selected from the Sloan Digital Sky Survey based on their emission line properties. The intrinsic luminosities of these quasars are thought to be in the range -24>M_B>-26, but optical obscuration implies that host galaxies can be studied unencumbered by bright nuclei. Each object has been imaged in three filters (`red', `green' and `blue') placed between the strong emission lines. The spectacular, high quality images reveal a wealth of details about the structure of the host galaxies and their environments. Most galaxies in the sample are ellipticals, but strong deviations from de Vaucouleurs profiles are found, especially in the blue band. We argue that most of these deviations are due to the light from the nucleus scattered off interstellar material in the host galaxy. This scattered component can make a significant contribution to the broad-band flux and complicates the analysis of the colors of the stellar populations in the host galaxy. This extended component can be difficult to notice in unobscured luminous quasars and may bias the results of host galaxy studies.Comment: 6 pages including 2 color figures; proceedings of the 'QSO host galaxies: evolution and environment' conference, Leiden, August 200

Resolving the ‘Nitrogen Paradox’ of arbuscular mycorrhizas : fertilization with organic matter brings considerable benefits for plant nutrition and growth

Arbuscular mycorrhizal fungi (AMF) can transfer nitrogen (N) to host plants but the ecological relevance is debated, as total plant N and biomass do not generally increase. The extent to which the symbiosis is mutually beneficial is thought to rely on the stoichiometry of N, phosphorus (P) and carbon (C) availability. While inorganic N fertilisation has been shown to elicit strong mutualism, characterised by improved plant and fungal growth and mineral nutrition, similar responses following organic N addition are lacking. Using a compartmented microcosm experiment, we determined the significance to a mycorrhizal plant of placing a 15N‐labelled, nitrogen‐rich patch of organic matter in a compartment to which only AMF hyphae had access. Control microcosms denied AMF hyphal access to the patch compartment. When permitted access to the patch compartment, the fungus proliferated extensively in the patch and transferred substantial quantities of N to the plant. Moreover, our data demonstrate that allowing hyphal access to an organic matter patch enhanced total plant N and P contents, with a simultaneous and substantial increase in plant biomass. Moreover, we demonstrate that organic matter fertilization of arbuscular mycorrhizal plants can foster a mutually beneficial symbiosis based on nitrogen transfer, a phenomenon previously thought irrelevant