Germination and Emergence of Primed Grass Seeds Under Field and Simulated-field Temperature Regimes

Seed priming may enhance establishment success of cool-seasonrange grasses which must compete with annual weeds for earlyspring moisture. Previous priming studies have confirmed germinationrate enhancement for these species but relative treatment effectsunder field-temperature conditions have not been assessed. Weprimed seeds of thickspike wheatgrass [Elymus lanceolatus(Scribn.and J. G. Smith) Gould], bluebunch wheatgrass [Pseudoroegneriaspicata(Pursh) Löve], Sandberg bluegrass (Poa sandbergiiVasey.) and bottlebrush squirreltail [Elymus elymoides(Raf.)Swezey] and evaluated their relative emergence rate in threesoil types as a function of spring-planting date. Germinationresponse was simultaneously evaluated in laboratory germinatorsthat were programmed to simulate the field-temperature regimeat planting depth. Seed priming enhanced both germination andemergence rate with the greatest effect occurring during theearlier, cooler planting dates. Total emergence and emergencerate in the field were lower than for the equivalent germinationresponse in the laboratory. Thermal-germination response wasmodelled and predictions developed for evaluating potentialgermination under late winter/early spring soil-temperatureregimes. Modelling results predicted that greater germinationenhancement would have been possible at earlier planting datesthan were measured in the field experiment.Copyright 2000 Annalsof Botany Company Bunchgrass, germination, emergence, priming, rate, temperature     

The Ovicidal,Larvacidal and Adulticidal Properties of 5,5′-Dimethyl-2,2′-Bipyridyl against Drosophila melanogaster

Insecticide resistance has limited the number of available chemical options for insect pest control. Hence there is a need for new chemistries with novel modes of action. Here we investigate the mode of action for an insecticide that has not yet been released for commercial use. The ovicidal, larvacidal and adulticidal effects of 5,5′-dimethyl -2, 2′-dipyridyl (termed Ha44), which is being developed as a treatment for head lice, were evaluated in the Drosophila melanogaster model system. Ha44 demonstrated significant activity against embryos and was capable of arresting development at a number of stages of embryogenesis. The effects of Ha44 on embryos was shown to be reversible following the addition of the metal ions Fe(II) and Fe(III), Cu and Zn. When larvae were exposed to Ha44, lethality was recorded at similar concentrations to those observed for embryos. Using an eYFP reporter system it was shown that Ha44 was able to reduce the levels of both copper and zinc in the digestive tract, confirming the binding of Ha44 to these metals in vivo. Ha44 has further been shown to inhibit a zinc containing metalloproteinase in vitro. Exposure of adult flies to Ha44 resulted in lethality, but at higher concentrations than those observed for embryos and larvae. The median lethal dose in adult flies was shown to be associated with the type of exposure, with an LD-50 of 1.57 mM being recorded following the direct contact of flies with Ha44, while an LD-50 of 12.29 mM was recorded following the ingestion of the compound. The capacity of Ha44 to act on all stages of the life-cycle and potentially via a range of targets suggests that target site resistance is unlikely to evolve.     

Population dynamics of a host-specific root-feeding cyst nematode and resource quantity in the root zone of a clonal grass

Recent studies have suggested that root-feeding nematodes influence plant community dynamics, but few studies have investigated the population dynamics of the nematodes. In coastal foredunes, feeding-specialist cyst nematodes ( Heterodera spp.) are dominant in the soil nematode community and greenhouse studies pointed at bottom-up control by their host plant. Here we examine the population dynamics of H. arenaria in the field in relation to resource quantity in the root zone of Ammophila arenaria (marram grass).
Ammophila arenaria is a pioneer grass in mobile coastal foredunes of northwestern and Mediterranean Europe. Every year, the plant expands clonally into freshly deposited layers of wind-blown sand, followed by dispersal and build-up of the nematode population into the new root zone. In a newly developing root zone the first H. arenaria cysts were observed one month after the first new roots were detected, indicating that nematode dispersal is not limiting the initial establishment of new populations. Throughout the growth season, the numbers of cysts, as well as the numbers of eggs and juveniles within cysts, were related to the quantity of roots. However, cyst density varied between years. Therefore, we conclude that in new root layers of A. arenaria cyst nematodes are bottom-up controlled by resource quantity, but that other factors, for example resource quality, influence the relation between nematode abundance and resource quantity.
In deeper root zones the nematode abundance declines over time. Here, numbers of cysts were not related to root biomass, while numbers of eggs and juveniles inside the cysts were weakly related. This points at other factors than resource quantity, for example the quality of the roots or unsuitable abiotic environmental conditions that have a stronger influence on cyst numbers than resource quantity. We discuss how bottom-up control of cyst nematodes may indirectly protect the plant against harmful root knot nematodes.     

In vitro propagation of <Emphasis Type="Italic">Helleborus</Emphasis> species

A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog 1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in a solution of indole-3-butyric acid (IBA -3 mg l⁻¹) and 1-naphthaleneacetic acid (NAA-1 mg l⁻¹) at 5°C.     

Morphiceptin and beta-casomorphin-5 analogues containing a reduced peptide bond: selective mu-receptor agonists and a novel mu antagonist, H-Tyr-Pro psi (CH2-NH)Phe-Pro-Gly-OH.

In order to prevent enzymatic degradation of beta-casomorphin-5 (1) and morphiceptin, reduced peptide bonds were incorporated at the 2-3 and 3-4 bonds, respectively. The analogues were synthesized by a combination of solid phase methodology and reductive alkylation of resin-bound peptide amines with Boc-amino acid aldehydes (Boc: tert-butyloxycarbonyl) in the presence of NaBH3CN. During reversed phase high pressure liquid chromatography purification, peak shape distortions could be observed. Epimerization was excluded, based on gas chromatography/mass spectroscopy analysis, which indicated acceptable levels of racemization (less than 3%) in the crude product. Instead, the phenomena could be attributed to slow cis/trans isomerizations originating from the Xxx-Pro bonds in the sequence. The presence of different conformational isomers was also established by 1H-nmr spectroscopy in DMSO-d6. All analogues showed high stability in blood plasma, enhanced binding affinity for the mu receptor, and very low binding to the delta receptor. While the Phe 3 psi(CH2-N)Pro4 analogues (3) and (5) displayed agonist activity, the Pro 2 psi(CH2-NH)Phe3 modified analogue (2) showed antagonist activity comparable to D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2.     

Effects of cycloheximide on the temperature profile of Sacharomyces cerevisiae

Tmax, the maximum temperature for growth of Saccharomyces cerevisiae, decreased linearly with increasing concentrations of cycloheximide added to the medium, to about 20 degrees C at 2.5 microgram ml-1. In this concentration range thermal death was not enhanced. The Arrhenius plot of growth was shifted to lower temperatures as a function of the cycloheximide concentration and became dissociated from the Arrhenius plot of thermal death. It was concluded that the target site of cycloheximide, the cytoplasmic ribosome, is not identical with the physiological Tmax site of S. cerevisiae and that the binding of cycloheximide to its target sites is strongly enhanced by the temperature.     

Optimal trypsin concentration for rat heart cell cultures

Three concentrations (0.5, 1 and 2 per 1000, w/v) of a single batch of trypsin were compared regarding their influence on cultured cardiac cell of newborn rats. All three allowed to obtain cardiac cells in good conditions, as evidence by beating frequencies and [16-14C]-palmitate beta-oxidation. However the 0.5 per 1000 concentration appeared to be the optimal one, inducing a smaller loss of cells during the first two days in culture.