DOES LIGHT QUALITY AFFECT THE SINKING RATES OF MARINE DIATOMS?1

Although the spectral quality of light in the ocean varies considerably with depth, the effect of light quality on different physiological processes in marine phytoplankton remains largely unknown. In cases where experiments are performed under full spectral irradiance, the meaning of these experiments in situ is thus unclear. In this study, we determined whether variations in spectral quality affected the sinking rates of marine diatoms. Semicontinuous batch cultures of Thalassiosira weissflogii (Gru.) Fryxell et Hasle and Ditylum brightwellii (t. West) Grunow in Van Huerk were grown under continuous red, white, or blue light. For T. weissflogii, sinking rates (SETCOL method) were twice as high (～0.2 m·d^?1)for cells grown under red light as for cells grown under white or blue light (～0.08 m·d^?1), but there were no significant differences in carbohydrate content (～105 fg·μm^?3) or silica content (～ 17 fg·μ^?3) to account for the difference in sinking rates. Thalassiosira weissflogii grown under blue light was significantly smaller (495 μm³) than cells grown under red light (661 μm³), which could contribute to its reduced sinking rate. However, cells grown under white light were similar in size to those grown under red light but had sinking rates not different from those of cells grown under blue light, indicating the involvement of factors other than size. There were no significant differences in sinking rate (～0.054 m·d^?1) or silica content (～20 fg·μm^?3) in D. brightwellii grown under red, white, or blue light, but cells grown under red light were significantly (20%) larger and contained significantly (20%) more carbohydrate per μm³ than cells grown under white or blue light. Spectral quality had no consistent effect on sinking rate, biochemical composition (carbohydrate or silica content), or cell volume in the two diatoms studied. The similarity in sinking rate of cells grown under white light compared to those grown under blue light supports the ecological validity of sinking rate studies done under white light.     

RELATIONSHIP BETWEEN NUCLEOSIDE DIPHOSPHATE KINASE ACTIVITY AND LIGHT-LIMITED GROWTH RATE IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1

Light-limited cultures of the marine diatom Thalassiosira pseudonana (Hustedt) Hasle and Heimdal (3H clone) were grown over a range of growth rates between 0.06 and 1.64 d^?1. Variations in cell volume, cell quotas of carbon, nitrogen, and protein, and maximal activity of the enzyme nucleoside diphosphate kinase (NDPK) were measured and examined as a function of growth rate. NDPK from T. pseudonana showed K_m values of 0.24 and 0.68 mM for thymidine 5′-diphosphate and adenosine 5′-triphosphate (ATP), respectively, which are similar to those found for NDPK from a variety of organisms, from bacteria to mammals. An apparent activation enthalpy of 3.52 kCal·mol^?1 was determined from Arrhenius plots. No thermodynamic transition points were noted over a temperature range from 10° to 25°C. NDPK activity was significantly correlated with growth rate but not with cell volume, carbon, nitrogen, or protein; for interspecific comparisons, normalization of enzyme activity to cell number may be most meaningful. NDPK activity per cell versus growth rate followed a U-shaped relationship, being relatively constant between 0.5 and 1.0 d^?1 and rising at higher and lower growth rates. Over this range, enzyme activity may be regulated by substrate concentration (ATP or other nucleoside triphosphates) or by adenylate energy charge. At higher growth rates where energy charge and substrate concentrations are probably high, changes in enzyme concentration appear to be required. The reasons for a rise in enzyme activity at low growth rate is unclear. Simultaneous measurement of nucleoside di- and triphosphate levels alongside NDPK measurements may help clarify the relationship, but these preliminary experiments indicate that NDPK is of limited usefulness as an index of in situ growth rate.     

An Ustilago maydis Mutant Partially Blocked in P45014DM Activity Is Hypersensitive to Azole Fungicides

An Ustilago maydis ergosterol biosynthesis mutant (A14) which is partially blocked in sterol 14alpha-demethylase (P45014DM) activity is described. This mutant accumulated the abnormal 14alpha-methyl sterols, eburicol, 14alpha-methylfecosterol, and obtusifoliol, along with significant amounts of ergosterol. Although the A14 mutant grew nearly as well as the wild type, it was impaired in cell extension growth, which indicated a dysfunction in apical cell wall synthesis. The mutant was also found to be hypersensitive to the azole fungicides penconazole and tebuconazole.     

Hexazonium pararosaniline as a fixative for animal tissues

Hexazonium pararosaniline is a valuable reagent that has been used in enzyme activity histochemistry for 50 years. It is an aqueous solution containing the tris-diazonium ion derived from pararosaniline, an aminotriarylmethane dye, and it contains an excess of nitrous acid that was not consumed in the diazotization reaction. Other investigators have found that immersion for 2 min in an acidic (pH 3.5) 0.0015 M hexazonium pararosaniline solution can protect cryostat sections of unfixed animal tissues from the deleterious effects of aqueous reagents such as buffered solutions used in immunohistochemistry, while preserving specific affinities for antibodies. In the present investigation hexazonium pararosaniline protected lymphoid tissue and striated muscle against the damaging effects of water or saline. The same protection was conferred on unfixed sections treated with dilute nitrous or hydrochloric acid in concentrations similar to those in hexazonium pararosaniline solutions. Model tissues (solutions, gels or films containing gelatin and/or bovine albumin) responded predictably to well known cross-linking (formaldehyde) or coagulant (mercuric chloride) fixatives. Hexazonium pararosaniline solutions prevented the dissolution of protein gels in water only after 9 or more days of contact, during which time considerable swelling occurred. It is concluded that there is no evidence for a “fixative” action of hexazonium pararosaniline. The protective effect on frozen sections of unfixed tissue is attributable probably to the low pH of the solution.     

Economic evaluation of water loss saving due to the biological control of water hyacinth at New Year’s Dam,Eastern Cape province,South Africa

Water hyacinth Eichhornia crassipes is considered the most damaging aquatic weed in the world. However, few studies have quantified the impact of this weed economically and ecologically, and even fewer studies have quantified the benefits of its control. This paper focuses on water loss saving as the benefit derived from biological control of this plant between 1990 and 2013 at New Year’s Dam, Alicedale, Eastern Cape, South Africa. Estimates of water loss due to evapotranspiration from water hyacinth vary significantly; therefore, the study used three different rates, high, medium and low. A conservative raw agriculture value of R 0.26 per m³ was used to calculate the benefits derived by the water saved. The present benefit and cost values were determined using 10% and 5% discount rates. The benefit/cost ratio at the low evapotranspiration rate was less than one, implying that biological control was not economically viable but, at the higher evapotranspiration rates, the return justified the costs of biological control. However, at the marginal value product of water, the inclusion of the costs of damage to infrastructure, or the adverse effects of water hyacinth on biodiversity, would justify the use of biological control, even at the low transpiration rate.     

The Tau/A152T mutation,a risk factor for frontotemporal‐spectrum disorders,leads to NR2B receptor‐mediated excitotoxicity

We report on a novel transgenic mouse model expressing human full‐length Tau with the Tau mutation A152T (hTau^AT), a risk factor for FTD‐spectrum disorders including PSP and CBD. Brain neurons reveal pathological Tau conformation, hyperphosphorylation, mis‐sorting, aggregation, neuronal degeneration, and progressive loss, most prominently in area CA3 of the hippocampus. The mossy fiber pathway shows enhanced basal synaptic transmission without changes in short‐ or long‐term plasticity. In organotypic hippocampal slices, extracellular glutamate increases early above control levels, followed by a rise in neurotoxicity. These changes are normalized by inhibiting neurotransmitter release or by blocking voltage‐gated sodium channels. CA3 neurons show elevated intracellular calcium during rest and after activity induction which is sensitive to NR2B antagonizing drugs, demonstrating a pivotal role of extrasynaptic NMDA receptors. Slices show pronounced epileptiform activity and axonal sprouting of mossy fibers. Excitotoxic neuronal death is ameliorated by ceftriaxone, which stimulates astrocytic glutamate uptake via the transporter EAAT2/GLT1. In summary, hTau^AT causes excitotoxicity mediated by NR2B‐containing NMDA receptors due to enhanced extracellular glutamate.     

In vitro evaluation of native entomopathogenic fungi and neem (Azadiractha indica) extracts on Spodoptera frugiperda

The control of Spodoptera frugiperda is based on synthetic insecticides, so some alternatives are the use of entomopathogenic fungi (EF) and neem extract. The objective of the study was to evaluate in vitro effectiveness of native EF and neem extracts on S. frugiperda larvae. Six EF were identified by DNA sequencing of ITS regions from three EF (Fusarium solani, Metarrhizium robertsii, Nigrospora spherica and Penicillium citrinum). They were evaluated in concentrations of 1 × 10⁸ spores/ mL. In addition, a second bioassay was carried out evaluating only F. solani, M. robertsii and N. sphaerica and the addition of vegetable oil. On the other hand, extraction of secondary metabolites from neem seed (Azadirachta indica) was carried out by performing, mass (g) and solvent volume (mL ethanol and water) combinations, which were subjected to microwaves and ultrasound. Subsequently, these extracts were evaluated in concentrations of 3%, 4% and 5%. A survival analysis was performed for each of the bioassays. With respect to the results of the first bioassay, F. solani obtained a probability of survival of 0.476 on the seventh day, while in the second bioassay, M. robertsii obtained 0.488 survival probability. This suggests that the expected percentage of larvae that stay alive on the sixth day is 48.8%. However, in the evaluation of the neem extract the combination 1:12/70% to 4% caused 84% mortality of larvae. The use of native HE and neem extracts has potential for the control of S. frugiperda.     

Analysis of the soluble matrix of vaterite otoliths of juvenile herring (Clupea harengus): do crystalline otoliths have less protein?

Otoliths are calcium carbonate concretions laid down in the inner ear of fish and used in fish age estimation. Otoliths precipitate in the form of aragonite but aberrant precipitation may result in vaterite formation instead of aragonite. Vaterite otoliths are more translucent than aragonite. The quantity of HCl-soluble proteins (SP) was measured in the vaterite otoliths and their aragonite pairs of one year old reared herring Clupea harengus to assess the changes induced by the precipitation of vaterite in the amount of soluble proteins in the otolith. Results showed that vaterite otoliths had as much soluble proteins as their aragonite pairs (p>0.05). Due to the lower density of the vaterite, vaterite otoliths were lighter than their aragonite pairs (p<0.05) which explained that protein concentrations were significantly higher (p<0.05) than in aragonite otoliths. These results indicate that the precipitation of vaterite in otoliths did not affect the inclusion of soluble proteins. Furthermore, they suggest that soluble proteins do not affect the translucent or opaque appearance of otoliths. Differences in translucency may instead be caused by the amounts of insoluble proteins or by differences in the physical properties of proteins. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of the otolith proteins revealed two bands at 50 and 62 kDa in both aragonite and vaterite otoliths suggesting that the precipitation of vaterite in the otolith is not controlled by either of these two proteins present in the otolith.