Grapevine powdery mildew (Erysiphe necator): a fascinating system for the study of the biology, ecology and epidemiology of an obligate biotroph

Few plant pathogens have had a more profound effect on the evolution of disease management than Erysiphe necator, which causes grapevine powdery mildew. When the pathogen first spread from North America to England in 1845, and onwards to France in 1847, 'germ theory' was neither understood among the general populace nor even generally accepted within the scientific community. Louis Pasteur had only recently reported the microbial nature of fermentation, and it would be another 30 years before Robert Koch would publish his proofs of the microbial nature of certain animal diseases. However, within 6 years after the arrival of the pathogen, nearly 6 million grape growers in France were routinely applying sulphur to suppress powdery mildew on nearly 2.5 million hectares of vineyards (Campbell, 2006). The pathogen has remained a focus for disease management efforts ever since. Because of the worldwide importance of the crop and its susceptibility to the disease, and because conventional management with modern, organic fungicides has been compromised on several occasions since 1980 by the evolution of fungicide resistance, there has also been a renewed effort worldwide to explore the pathogen's biology and ecology, its genetics and molecular interactions with host plants, and to refine current and suggest new management strategies. These latter aspects are the subject of our review. Taxonomy: The most widely accepted classification follows. Family Erysiphaceae, Erysiphe necator Schw. [syn. Uncinula necator (Schw.) Burr., E. tuckeri Berk., U. americana Howe and U. spiralis Berk. & Curt; anamorph Oidium tuckeri Berk.]. Erysiphe necator var. ampelopsidis was found on Parthenocissus spp. in North America according to Braun (1987), although later studies revealed isolates whose host range spanned genera, making the application of this taxon somewhat imprecise (Gadoury and Pearson, 1991). The classification of the genera before 1980 was based on features of the mature ascocarp: (i) numbers of asci; and (ii) morphology of the appendages, in particular the appendage tips. The foregoing has been supplanted by phylogeny inferred from the internal transcribed spacer (ITS) of ribosomal DNA sequences (Saenz and Taylor, 1999), which correlates with conidial ontogeny and morphology (Braun et al., 2002). Host range: The pathogen is obligately parasitic on genera within the Vitaceae, including Vitis, Cissus, Parthenocissus and Ampelopsis (Pearson and Gadoury, 1992). The most economically important host is grapevine (Vitis), particularly the European grape, V. vinifera, which is highly susceptible to powdery mildew. Disease symptoms and signs: In the strictest sense, macroscopically visible mildew colonies are signs of the pathogen rather than symptoms resulting from its infection, but, for convenience, we describe the symptoms and signs together as the collective appearance of colonized host tissues. All green tissues of the host may be infected. Ascospore colonies are most commonly found on the lower surface of the first-formed leaves near the bark of the vine, and may be accompanied by a similarly shaped chlorotic spot on the upper surface. Young colonies appear whitish and those that have not yet sporulated show a metallic sheen. They are roughly circular, ranging in size from a few millimetres to a centimetre or more in diameter, and can occur singly or in groups that coalesce to cover much of the leaf. Senescent colonies are greyish, and may bear cleistothecia in various stages of development. Dead epidermal cells often subtend the colonized area, as natural mortality in the mildew colony, the use of fungicides, mycoparasites or resistance responses in the leaf result in the deaths of segments of the mildew colony and infected epidermal cells. Severely affected leaves usually senesce, develop necrotic blotches and fall prematurely. Infection of stems initially produces symptoms similar to those on leaves, but colonies on shoots are eventually killed as periderm forms, producing a dark, web-like scar on the cane (Gadoury et al., 2011). Inflorescences and berries are most susceptible when young, and can become completely coated with whitish mildew. The growth of the berry epidermal tissue stops when severely infected, which may result in splitting as young fruit expand. Berries in a transitional stage between susceptible and resistant (generally between 3 and 4 weeks after anthesis) develop diffuse, nonsporulating mildew colonies only visible under magnification. Diffuse colonies die as berries continue to mature, leaving behind a network of necrotic epidermal cells (Gadoury et al., 2007). Survival over winter as mycelium in buds results in a distinctive foliar symptom. Shoots arising from these buds may be heavily coated with fungal growth, stark white in colour and stand out like white flags in the vine, resulting in the term 'flag shoots'. More commonly, colonization of a flag shoot is less extensive, and infection of a single leaf, or of leaves on one side of the shoot only, is observed (Gadoury et al., 2011).     

Magnitude of head impact exposures in individual collegiate football players

The purpose of this study was to quantify the severity of head impacts sustained by individual collegiate football players and to investigate differences between impacts sustained during practice and game sessions, as well as by player position and impact location. Head impacts (N = 184,358) were analyzed for 254 collegiate players at three collegiate institutions. In practice, the 50th and 95th percentile values for individual players were 20.0 g and 49.5 g for peak linear acceleration, 1187 rad/s2 and 3147 rad/s2 for peak rotational acceleration, and 13.4 and 29.9 for HITsp, respectively. Only the 95th percentile HITsp increased significantly in games compared with practices (8.4%, p = .0002). Player position and impact location were the largest factors associated with differences in head impacts. Running backs consistently sustained the greatest impact magnitudes. Peak linear accelerations were greatest for impacts to the top of the helmet, whereas rotational accelerations were greatest for impacts to the front and back. The findings of this study provide essential data for future investigations that aim to establish the correlations between head impact exposure, acute brain injury, and long-term cognitive deficits.     

Thermodynamics of Ni2+, Cu2+, and Zn2+ binding to the urease metallochaperone UreE

The two Ni2+ ions in the urease active site are delivered by the metallochaperone UreE, whose metal binding properties are central to the assembly of this metallocenter. Isothermal titration calorimetry (ITC) has been used to quantify the stoichiometry, affinity, and thermodynamics of Ni2+, Cu2+, and Zn2+ binding to the well-studied C-terminal truncated H144*UreE from Klebsiella aerogenes, Ni2+ binding to the wild-type K. aerogenes UreE protein, and Ni2+ and Zn2+ binding to the wild-type UreE protein from Bacillus pasteurii. The stoichiometries and affinities obtained by ITC are in good agreement with previous equilibrium dialysis results, after differences in pH and buffer competition are considered, but the concentration of H144*UreE was found to have a significant effect on metal binding stoichiometry. While two metal ions bind to the H144*UreE dimer at concentrations <10 microM, three Ni2+ or Cu2+ ions bind to 25 microM dimeric protein with ITC data indicating sequential formation of Ni/Cu(H144*UreE)4 and then (Ni/Cu)2(H144*UreE)4, or Ni/Cu(H144*UreE)2, followed by the binding of four additional metal ions per tetramer, or two per dimer. The thermodynamics indicate that the latter two metal ions bind at sites corresponding to the two binding sites observed at lower protein concentrations. Ni2+ binding to UreE from K. aerogenes is an enthalpically favored process but an entropically driven process for the B. pasteurii protein, indicating chemically different Ni2+ coordination to the two proteins. A relatively small negative value of DeltaCp is associated with Ni2+ and Cu2+ binding to H144*UreE at low protein concentrations, consistent with binding to surface sites and small changes in the protein structure.     

Using gigartinine to track the distribution of an alien species of <Emphasis Type="Italic">Gracilaria</Emphasis> in New Zealand

The presence of gigartinine has been used previously as a taxonomic marker for the positive identification in Manukau Harbour (west coast, Auckland) of Gracilaria sp., which has apparently been introduced to New Zealand waters and is easily confused morphologically with the native species, G. chilensis. Thirty two estuarine/harbour populations of Gracilaria in New Zealand were screened for the presence of gigartinine to further test the utility of gigartinine as a reliable species marker. DNA fingerprinting was used to confirm the identity of a subset of the specimens surveyed. Using genetic rather than chemical characterisation, it was discovered that Gracilaria sp. is also present in Orakei Basin (east coast, Auckland). Although a sample from the wild did not have the anticipated gigartinine content, tank cultivation of thalli from this population in an artificially elevated nitrogen environment allowed the plant to accumulate nitrogen as gigartinine. This confirmed the unusual ability of this species of Gracilaria to store nitrogen in this form, unlike the widespread, morphologically similar, G. chilensis.     

Roles of vasoconstrictor prostaglandins, COX-1 and -2, and AT1, AT2, and TP receptors in a rat model of early 2K,1C hypertension

Angiotensin (ANG) II activating type 1 receptors (AT(1)Rs) enhances superoxide anion (O(2)*(-)) and arachidonate (AA) formation. AA is metabolized by cyclooxygenases (COXs) to PGH(2), which is metabolized by thromboxane (Tx)A(2) synthase to TxA(2) or oxidized to 8-isoprostane PGF(2alpha) (8-Iso) by O(2)*(-). PGH(2), TxA(2), and 8-Iso activate thromboxane-prostanoid receptors (TPRs). We investigated whether blood pressure in a rat model of early (3 wk) two-kidney, one-clip (2K,1C) Goldblatt hypertension is maintained by AT(1)Rs or AT(2)Rs, driving COX-1 or -2-dependent products that activate TPRs. Compared with sham-operated rats, 2K,1C Goldblatt rats had increased mean arterial pressure (MAP; 120 +/- 4 vs. 155 +/- 3 mmHg; P < 0.001), plasma renin activity (PRA; 22 +/- 7 vs. 48 +/- 5 ng x ml(-1) x h(-1); P < 0.01), plasma malondialdehyde (1.07 +/- 0.05 vs. 1.58 +/- 0.16 nmol/l; P < 0.01), and TxB(2) excretion (26 +/- 4 vs. 51 +/- 7 ng/24 h; P < 0.01). Acute graded intravenous doses of benazeprilat (angiotensin-converting enzyme inhibitor) reduced MAP at 20 min (-36 +/- 5 mmHg; P < 0.001) and excretion of TxA(2) metabolites. Indomethacin (nonselective COX antagonist) or SC-560 (COX-1 antagonist) reduced MAP at 20 min (-25 +/- 5 and -28 +/- 7 mmHg; P < 0.001), whereas valdecoxib (COX-2 antagonist) was ineffective (-9 +/- 5 mmHg; not significant). Losartan (AT(1)R antagonist) or SQ-29548 (TPR antagonist) reduced MAP at 150 min (-24 +/- 6 and -22 +/- 3 mmHg; P < 0.001), whereas PD-123319 (AT(2)R antagonist) was ineffective. Acute blockade of TPRs, COX-1, or COX-2 did not change PRA, but TxB(2) generation by the clipped kidney was reduced by blockade of COX-1 and increased by blockade of COX-2. 2K,1C hypertension in rats activates renin, O(2)*(-), and vasoconstrictor PGs. Hypertension is maintained by AT(1)Rs and by COX-1, but not COX-2, products that activate TPRs.     

Hydrogen peroxide mediates a transient vasorelaxation with tempol during oxidative stress

Tempol catalyzes the formation of H(2)O(2) from superoxide and relaxes blood vessels. We tested the hypothesis that the generation of H(2)O(2) by tempol in vascular smooth muscle cells during oxidative stress contributes to the vasorelaxation. Tempol and nitroblue tetrazolium (NBT) both metabolize superoxide in vascular smooth muscle cells, but only tempol generates H(2)O(2). Rat pressurized mesenteric arteries were exposed for 20 min to the thromboxane-prostanoid receptor agonist, U-46619, or norepinephrine. During U-46619, tempol caused a transient dilation (22 +/- 2%), whereas NBT was ineffective (2 +/- 1%), and neither dilated vessels constricted with norepinephrine, which does not cause vascular oxidative stress. Neither endothelium removal nor blockade of K(+) channels with 40 mM KCl affected the tempol-induced dilation, but catalase blunted the tempol dilation by 53 +/- 7%. Tempol, but not NBT, increased H(2)O(2) in rat mesenteric vessels detected with dichlorofluorescein. To test physiological relevance in vivo, topical application of tempol caused a transient dilation (184 +/- 20%) of mouse cremaster arterioles exposed to angiotensin II for 30 min, which was not seen with NBT (9 +/- 4%). The vasodilation to tempol was reduced by 68 +/- 6% by catalase. We conclude that the transient relaxation of blood vessels by tempol after prolonged exposure to U-46619 or angiotensin II is mediated in part via production of H(2)O(2) and is largely independent of the endothelium and potassium channels.     

Montane Meadows: A Soil Carbon Sink or Source?

Ecosystems - As the largest biogeochemically active terrestrial reserve of carbon (C), soils have the potential to either mitigate or amplify rates of climate change. Ecosystems with large C stocks...