Indirect assessment of callus fresh weight by non-destructive methods

The size of callus of Nicotiana plumbaginifolia was measured by determinations of fresh weight (FW), area (electronic planimeter and a point-counting method) and width (standard width and greatest width). All these methods, with the exception of the standard width measurements, were found to produce adequate substitutes for fresh weight.Particular advantages apply to the use of the point-counting method, but the relationship between callus area and point interval was found to be critically important in determining the accuracy of measurements. The use of surface dimensions rather than FW permits continuous measurement of callus size without disturbance of the callus or its environment within the containers.Abbreviation FW fresh weight     

17O]oxygen hyperfine structure for the hydroxyl and superoxide radical adducts of the spin traps DMPO, PBN and 4-POBN

[17O]oxygen hyperfine coupling constants are reported for the superoxide and hydroxyl radical adducts with the spin traps 5,5-dimethyl-1-pyrroline N-oxide, N-t-butyl-alpha-phenylnitrone and alpha-(4-pyridyl 1-oxide)-N-t-butylnitrone. These couplings provide spectroscopic evidence that the spin adducts have been correctly identified.     

Linking Mosquito Infestation to Resident Socioeconomic Status, Knowledge, and Source Reduction Practices in Suburban Washington, DC

Eliminating water-holding containers where mosquitoes oviposit and develop (source reduction) can help manage urban disease-vector mosquitoes. Source reduction requires residents to be knowledgeable of effective practices and motivated to implement them. We tested relationships between demographics, resident knowledge, attitudes, and practices (KAP), and mosquito infestation by administering larval mosquito surveys and KAP questionnaires in Washington, DC. Respondents who reported practicing source reduction had lower numbers of pupae-positive containers and Culex pipiens-positive containers, but not Aedes albopictus-positive containers or water-holding containers, in their yards. When controlling for numbers of water-holding containers in statistical models, residents who reported source reduction had lower numbers of A. albopictus-positive containers in addition to numbers of pupae-positive containers and C. pipiens-positive containers. These results suggest that while active container reduction may be effective at reducing C. pipiens and overall pupal production, it may be offset by other resident activities that add containers to yards, and that source reduction that involves mosquito habitat management without outright container removal can also be effective at reducing A. albopictus. Source reduction was related to respondent knowledge of mosquitoes and, in particular, specific knowledge of mosquito development, which both varied with demographics alongside respondent motivation to control mosquitoes. Respondents from high socioeconomic status households reported greater knowledge but lower motivation than respondents from middle and low socioeconomic-status households. We conclude that mosquito-related education will help promote community-based container management as part of integrated mosquito management programs, particularly in middle and low socioeconomic status neighborhoods with lower knowledge and high motivation.     

Revisiting the interaction of the radical anion metabolite of nitrofurantoin with glutathione.

There have been several conflicting reports as to the scavenging nature of glutathione toward the nitro radical anion of the drug nitrofurantoin. We produced the radical anion enzymatically using the xanthine oxidase/hypoxanthine system at pH 7.4 and pH 9.0 in the presence of various levels of glutathione from 10 to 100 mM and monitored any changes in the radical concentration via electron spin resonance spectroscopy. Independent of glutathione concentration, there was no decrease in the steady-state concentration of the radical. In fact, there was an average 30% increase in the concentration of the radical anion, which suggests enhanced enzyme activity in the presence of glutathione (GSH). These results, together with observations of the effects of glutathione on the stability of the radical anion generated by radiolysis or dithionite, rule out any detectable reaction between the nitrofurantoin radical anion and GSH under physiologically relevant conditions.     

A direct electron spin resonance and spin-trapping investigation of peroxyl free radical formation by hematin/hydroperoxide systems

Direct electron spin resonance was used to detect tert-alkylperoxyl radicals generated by hematin and the corresponding hydroperoxides at near-physiological pH values. The spin-trapping method was necessary to detect the less persistent primary ethylperoxyl radical. Under a nitrogen atmosphere, the electron spin resonance signal of the tert-alkylperoxyl radicals decreased, and the ethylperoxyl spin-adduct concentration did not change. Concomitant studies, using a Clark oxygen electrode, show that oxygen was consumed by the hematin-tert-alkyl hydroperoxide systems, but was released by the hematin-ethyl hydroperoxide reaction. Thus, molecular oxygen seems to play a subsidiary role in the hematin-catalyzed decomposition of hydroperoxides. Based on the electron spin resonance and oxygen electrode results, a mechanism for the continuous production of the peroxyl free radicals is proposed for hematin/hydroperoxide systems. The present spectroscopic methodology can be used to search for peroxyl free radical formation by hemoprotein/hydroperoxide systems.     

Experimental evidence that group foragers can converge on predicted producer-scrounger equilibria

When foraging together, animals are often observed to feed from food discoveries of others. The producer-scrounger (PS) game predicts how frequently this phenomenon of food parasitism should occur. The game assumes: (1) at any moment all individuals can unambiguously be categorized as either playing producer (searching for undiscovered food resources) or scrounger (searching for exploitation opportunities), and (2) the payoffs received from the scrounger tactic are negatively frequency dependent; a scrounger does better than a producer when the scrounger tactic is rare, but worse when it is common. No study to date has shown that the payoffs of producer and scrounger conform to the game's assumptions or that groups of foragers reach the predicted stable equilibrium frequency (SEF) of scrounger, whereby both tactics obtain the same payoff. The current study of three captive flocks of spice finches, Lonchura punctulata, provides the first test of the PS game using an apparatus in which both assumptions of the PS game are met. The payoffs to the scrounger, measured as feeding rate (seeds/s), were highly negatively frequency dependent on the frequency of scrounger. The feeding rate for scrounger declined linearly while the rate for producer either declined only slightly or not at all with increasing scrounger frequency. When given the opportunity to alternate between tactics, the birds changed their use of each, such that the group converged on the predicted SEF of scrounger after 5-8 days of testing. Individuals in this study, therefore, demonstrated sufficient plasticity in tactic use such that the flock foraged at the SEF of scrounger. Copyright 2000 The Association for the Study of Animal Behaviour.     

Sulfur-centered radical formation from the antioxidant dihydrolipoic acid

Lipoic acid and its reduced form, dihydrolipoic acid, are thought to be strong antioxidants. There are also reports of dihydrolipoic acid acting as a pro-oxidant under certain circumstances. This article reports the direct observation by ESR spectrometry of the disulfide radical anion and the spin trapping of the primary thiyl radical formed from the oxidation of dihydrolipoic acid through thiol pumping with phenol and horseradish peroxidase. The disulfide radical anion reacts rapidly with oxygen to form the reactive radical superoxide, which is also trapped. The radical species formed show a potential for pro-oxidant activity of this compound. Although antioxidants, in general, have been shown to have pro-oxidant potential, the pro-oxidant chemistry of dihydrolipoic acid has not been well characterized.     

On the use of organic extraction in the spin-trapping technique as applied to biological systems

A back-extraction methodology is presented which involves extraction of a spin adduct from an organic medium into an aqueous medium where its spectral parameters are well established. This technique should prove very useful in properly identifying spin adducts formed in organic media. Some of the hazards of extracting spin adducts into organic solvents for study are pointed out.     

In vitro culture of cell aggregates of rye (Secale cereale L.) at low densities

The growth of cell aggregates from a rye suspension culture was tested at low density in three culture systems. Mass seeding was the most supportive system, followed by agarose droplets. Microdroplet culture using Cuprak dishes was the least effective system. Growth was stimulated by the presence of a feeder layer of suspension cells but only if the feeder contact with the nursed cells was via a liquid and not a gaseous phase. Plating efficiences were enhanced by the feeder effect, whereas the subsequent growth rates were less affected. The techniques described should prove useful in programs aimed at the in vitro genetic manipulation of rye or other cereals.Abbreviations 2,4-D 2, 4 — dichlorophenoxy acetic acid - PE Plating efficiency