Absence of Eclipse Phase in Scrapie Mice

Field, Joyce and Keith¹ have claimed that the scrapie agent shows a viral characteristic by having an eclipse phase after being inoculated into the intracerebral region of mice. Three experiments, studying the accumulation of scrapie agent in spleen after intracerebral and intraperitoneal inoculation of mice, have not verified the conclusions of Field et al. A typical curve for the progression of scrapie activity after intracerebral inoculation (Fig. 1) shows no eclipse phase, nor was any observed in an experiment where the titre was examined every 2 days for the first 14 days after inoculation. Moreover, Field and his colleagues have not referred to similar studies with different results from theirs. Four independent groups of workers^2–6 have now examined the levels of scrapie activity in brain and spleen during the early stages after infection by three different routes and in none of these studies was there any clear indication of an eclipse phase in scrapie.     

A Germination Inhibitor from Sugar-Beet

There is present in the water extract of sugar-beet seed ballsan unsaturated yellow oil which is capable of inhibiting germinationof various seeds. It also inhibits salt uptake and the respirationof sugar-beet tissue disks. The activity of the polyphenolaseenzyme present in beet tissue is also depressed. The role ofthe oil in inhibition of sugar-beet germination is discussed.     

2-Methylhopanoids are maximally produced in akinetes of Nostoc punctiforme: geobiological implications

2-Methylhopanes, molecular fossils of 2-methylbacteriohopanepolyol (2-MeBHP) lipids, have been proposed as biomarkers for cyanobacteria, and by extension, oxygenic photosynthesis. However, the robustness of this interpretation is unclear, as 2-methylhopanoids occur in organisms besides cyanobacteria and their physiological functions are unknown. As a first step toward understanding the role of 2-MeBHP in cyanobacteria, we examined the expression and intercellular localization of hopanoids in the three cell types of Nostoc punctiforme : vegetative cells, akinetes, and heterocysts. Cultures in which N. punctiforme had differentiated into akinetes contained approximately 10-fold higher concentrations of 2-methylhopanoids than did cultures that contained only vegetative cells. In contrast, 2-methylhopanoids were only present at very low concentrations in heterocysts. Hopanoid production initially increased threefold in cells starved of nitrogen but returned to levels consistent with vegetative cells within 2 weeks. Vegetative and akinete cell types were separated into cytoplasmic, thylakoid, and outer membrane fractions; the increase in hopanoid expression observed in akinetes was due to a 34-fold enrichment of hopanoid content in their outer membrane relative to vegetative cells. Akinetes formed in response either to low light or phosphorus limitation, exhibited the same 2-methylhopanoid localization and concentration, demonstrating that 2-methylhopanoids are associated with the akinete cell type per se . Because akinetes are resting cells that are not photosynthetically active, 2-methylhopanoids cannot be functionally linked to oxygenic photosynthesis in N.   punctiforme .     

Two new genera, Crassoseta and Brachysternopsis, of the family Diplogyniidae (Acari, Mesostigmata, Trigynaspida)

The genus Crassoseta is erected for three new species of diplogyniid mites taken from passalid beetles collected in Mexico, Brazil and Costa Rica; Brachysternum cornutum Hyatt, 1964 is transferred to this genus and a key to species is given. Brachysternopsk gen.n. is established for B. flechtmanni gen. et sp.n. taken from an ant, Atrica capiguara. in Brazil.     

Susceptibility of willow clones (Salix spp.) to herbivory by Phyllodecta vulgatissima (L.) and Galerucella lineola (Fab.) (Coleoptera, Chrysomelidae)

Levels of damage by mixed natural infestations of the leaf-feeding chrysomelid beetles, Phyllodecta vulgatissima (L.) (the blue willow beetle) and Galerucella lineola (Fab.) (the brown willow beetle), were determined in replicated field plots of 24 Salix clones at Long Ashton (Bristol, UK) during 1993–94. Over the same period, the host plant preferences of both chrysomelids were investigated in a standard multiple-choice laboratory procedure, where beetles were enclosed in Petri dishes with leaf discs cut from young pot-grown trees propagated from shoot cuttings taken from 20 of the 24 willow clones represented in the field study. The laboratory experiments indicated that P. vulgatissima and G. lineola had similar host plant preferences in the range of willows examined (r >0.85). In both field and laboratory, the least preferred Salix clones and hybrids were those of 5. eriocephala, followed by S. purpurea, S. burjatica, S. dasyclados and S. triandra. Clones of S. eriocephala and S. purpurea were frequently rejected altogether in laboratory tests. Most preferred were clones of S. viminalis and several hybrids of S. viminalis, S. aurita, S. caprea and S. cinerea. These results substantiate the reports that P. vulgatissima and G. lineola are deterred from feeding on willows which have relatively high concentrations of phenolic (salicylate) glucosides in the leaves. The least preferred willows, particularly S. eriocephala, S. purpurea and S. burjatica, could be of great potential value in plant breeding for resistance to these willow beetle pests.