A new indolic antiauxin, α-(5,7-dichloroindole-3-)isobutyric acid: its chemical synthesis and biological activity

Summary A new potent antiauxin, -(5,7-dichloroindole-3-)isobutyric acid has been synthesized and shown to inhibit auxin-mediated elongation ofAvena coleoptiles and to stimulate root growth of rice seedlings. Its activity is stronger than -(p-chlorophenoxy)isobutyric acid and is comparable to that of 2,3,5-triiodobenzoic acid, which are typical antiauxins.     

In vivo effects of immunostimulating lipopeptides on mouse liver microsomal cytochromes P-450 and on paracetamol-induced toxicity

Summary Immunomodulating lipopeptides lauroyl-L-Ala--D-Glu-LL-A2pmNH2-Gly (RP 44.102) and lauroyl-L-Ala--D-Glu-LL-A2pmNH2 (RP 56.142) were found to protect mice against the hepatotoxicity of paracetamol, which is due to cytochrome P-450 dependent formation of toxic metabolites and radicals. In fact they decreased the amount of hepatic microsomal cytochrome P-450, and the level of CCl₄-induced lipid peroxidation. In contrast lauroyl-L-Ala--D-Glu-DD-A2pmNH2 (RP 53.204), which only differs by the configuration of the two chiral carbons of A2pm (diaminopimelic acid) and is not an immunomodulating agent, failed to protect against poisoning by paracetamol and had no effect on the level of hepatic cytochrome P-450 or the microsomal CCl₄-induced lipid peroxidation. This provides a clear connection between the immunostimulating properties of a compound and its effects on xenobiotic biotransformations.     

Evolutionary and ecological implications of cardenolide sequestration in the monarch butterfly

Summary Monarch butterflies sequester cardenolides from their larval host plants in the milkweed genusAsclepias for use in defense against predation. Of 108Asclepias species in North America, monarchs are known to feed as larvae on 27. Research on 11 of these has shown that monarchs sequester cardenolides most effectively, to an asymptote of approximately 350 g/0.1 g dry butterfly, from plants with intermediate cardenolide contents rather than from those with very high or very low cardenolide contents. SinceAsclepias host plant species are distributed widely in space and time across the continent, monarchs exploit them by migration between breeding and overwintering areas. After overwintering in central Mexico, spring migrants east of the Rocky Mountains exploit three predominantAsclepias species in the southern USA that have moderately high cardenolide contents. Monarchs sequester cardenolides very effectively from these species. First generation butterflies are thus well protected against predators and continue the migration north. Across the northern USA and southern Canada most summer breeding occurs on a fourthAsclepias species and in autumn most of these monarchs migrate back to Mexican overwintering sites. The ecological implications of this cycle of cardenolide sequestration for the evolution of monarch migration are discussed.     

Chemical ecology of oviposition in phytophagous insects

Summary Selection of a suitable site for oviposition by phytophagous insects is critical for successful development of the offspring. The behavioral events leading to oviposition are mediated to a large extent by chemical cues associated with potential host plants. Orientation and landing are primarily guided by volatile constituents of a plant, whereas assessment of a leaf surface depends on contact stimuli. Chemical mechanisms that ensure adequate spacing of progeny on limited resources include the production of oviposition-deterring pheromones as well as recognition of plant constituents released as a result of previous damage. Perception of chemical cues that affects oviposition involves receptors on antennae, tarsi, mouthparts or the ovipositor. Complex behavior such as tarsal drumming or stem runs may serve to provide increased receptor contact with chemical stimuli. Abiotic and biotic environmental factors often influence the production or release of behavior-modifying chemicals by a plant, and therefore affect oviposition preferences. Plant chemistry may be involved in associative learning, but may also lead to mistakes. Thus a clear correlation between oviposition preference and offspring success does not always exist.     

Failure of opioids to affect excitation and contraction in isolated ventricular heart muscle

Summary The opioid agonists morphine (selective for -receptors) and ethylketocyclazocine (selective for kappa-receptors), at concentrations evoking strong effects in neuronal structures, did not significantly affect the configuration of the intracellularly recorded action potential and the force of contraction in ventricular heart muscle isolated from guinea pigs, rabbits and man. These results suggest that any changes of heart functions in vivo in response to opioid-like drugs are probably not mediated postsynaptically at the myocardial cell membrane but rather presynaptically, influencing the release of noradrenaline and/or acetylcholine from the nerve terminals.     

The pineal and melatonin: Regulators of circadian function in lower vertebrates

Summary The pineal has been identified as a major circadian pacemaker within the circadian system of a number of lower vertebrates although other pacemaking sites have been implicated as well. The rhythmic synthesis and secretion of the pineal hormone, melatonin, is suggested as the mechanism by which the pineal controls circadian oscillators located elsewhere. Both light and temperature cycles can entrain the pineal melatonin rhythm. The pineal, therefore, acts as a photo and thermoendocrine transducer which functions to synchronize internal cycle with cycles in the environment. A model is presented which portrays the pineal as a major component of a multioscillator circadian system and which suggests how these multiple circadian clocks are coupled to each other and to cycles of light and temperature in the external world.     

The role of repair in radiobiology

Summary Apart from cancer and mutation induction, radiobiological effects on mammals are mostly attributable to cell death, defined as loss of proliferative capacity. Survival curves relate retention of that capacity to radiation dose, and often manifest a quasi-threshold (shoulder). The shoulder is attributable to an initial mechanism of repair (Q-repair) which is gradually depleted as dose increases. Another form of repair, which is not depleted (P-repair), increases the dose required to deliver an average of one lethal event per cell (dose D₀). Neither form of repair can unambiguously be linked with repair of defects in isolated DNA. An important initial lesion may well be disruption of the complex structural relationship between the DNA, nuclear membrane and associated proteins. One form of P-repair may be restoration of that structural relationship.     

Comments on “aggregation of equivalence relations” by P. C. Fishburn and A. Rubinstein

The theorem of the paper Aggregation of Equivalence Relations, by Fishburn and Rubinstein, states a result already known. This theorem improves a result from Mirkin (1975) and appears as a corollary occurring in Leclerc (1984).

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Resume L'unique théorème de l'article Aggregation of Equivalence Relations de Fishburn et Rubinstein est déja connu. Il améliore, en fait, un résultat de Mirkin (1975) et apparait en tant que corollaire dans Leclerc (1984).

     

Clustering the rows and columns of a contingency table

A number of ways of investigating heterogeneity in a two-way contingency table are reviewed. In particular, we consider chi-square decompositions of the Pearson chi-square statistic with respect to the nodes of a hierarchical clustering of the rows and/or the columns of the table. A cut-off point which indicates significant clustering may be defined on the binary trees associated with the respective row and column cluster analyses. This approach provides a simple graphical procedure which is useful in interpreting a significant chi-square statistic of a contingency table.The author gratefully acknowledges the constructive comments of the referees and the editor.     

Methodological foundations of systems methodologies

In social systems science generally, and in management science particularly, recent developments in the variety of types of specific problem-solving methodologies (under the rubric of hard and soft systems approaches) have given an impetus to a line of inquiry, as well as debate on the nature of those methodologies. On the one hand, there has been the view that what we are witnessing is a form of Kuhnian crisis. On the other hand, a complementarist view of developments has been argued and a contingency approach proposed. But one thing has been common among the competing views: a belief that the prospects for further advances in the design and application of those methodologies, and in resolving the current controversies, lie in serious attempts to reconsider and clarify the underlying metatheoretical assumptions and concerns. This paper is an attempt to contribute to such an endeavor. A brief exposition of three methodological foundations (namely, empiricism, hermeneutics, and critique) is made, not only with the purpose of highlighting the nature as well as the limits of their epistemological and ethical claims, but also as a basis for illuminating both the nature of contemporary work on systems inquiry, design, and problem solving and the ongoing debate on what constitutes appropriate criteria for choice of specific methodologies.